CHAPTER MISSION Replace “adequacy equals Kt/V” with a bedside adequacy system: assess the patient first, measure small-solute clearance correctly, separate peritoneal from residual kidney contributions, recognise why residual kidney function has disproportionate clinical value, preserve it deliberately, and troubleshoot an apparent clearance failure before simply adding more dialysis.

Figure 7.1 — Adequacy is a dashboard, not a single gauge.

High-quality PD integrates symptoms and life goals, sodium/volume balance, biochemical control, measured small-solute clearance and residual kidney function. No single metric can substitute for the whole dashboard.

MASTER PRINCIPLE Weekly Kt/V urea is a useful small-solute accounting tool. It is not a patient outcome, not a measure of sodium balance, and not proof that the person is clinically well. Treat the patient, preserve the kidneys, and use clearance measurements to explain or verify the clinical picture.

0. One-page chapter map

Table 7.1 — The eight decisions that govern PD adequacy.

Decision	Core question	Bedside output
1. Patient	Are symptoms, function, nutrition and life goals acceptable?	Clinical adequacy statement
2. Volume	Is sodium/water balance controlled?	Euvolemia plan
3. Delivery	Was the prescription actually delivered?	Delivered-dose verification
4. Kidney contribution	How much urine and renal clearance remain?	RKF measurement + trend
5. Small solutes	What do weekly Kt/V and related clearance measures show?	Clearance interpretation
6. Cause	If a target fails, is it measurement, delivery, RKF loss, membrane, access or prescription?	Named mechanism
7. Correct	Which prescription lever addresses that mechanism?	Targeted change
8. Verify	Did the patient and the relevant metric improve?	Reassessment + next trigger

Learning outcomes

Define high-quality PD adequacy as a multidimensional clinical state rather than a single clearance target.
Explain what weekly Kt/V urea measures, how its peritoneal and renal components are obtained, and where the metric can mislead.
Apply the ISPD evidence position that higher peritoneal small-solute clearance above conventional targets has not shown survival benefit.
Measure residual kidney function using timed urine and the mean of renal urea and creatinine clearances.
Explain why residual kidney function and urine volume carry clinical value beyond their numerical contribution to total Kt/V.
Distinguish a true small-solute shortfall from collection error, nonadherence, catheter/drain dysfunction, loss of RKF and volume-driven symptoms.
Use a mechanism-based strategy to preserve residual kidney function while avoiding both chronic fluid overload and iatrogenic volume depletion.
Adjust incremental PD as residual kidney function changes without treating a single Kt/V value as the whole prescription.

EVIDENCE POSTURE ISPD 2020 reframes adequacy as high-quality, goal-directed PD. The 2019 solute/fluid update found poor-quality evidence for small-solute targets, no survival advantage from pushing weekly Kt/V above 1.7, and only weak evidence supporting a weekly Kt/V of at least 1.7 in anuric adults. CANUSA reanalysis showed strong outcome associations with residual GFR and urine volume but not equivalent peritoneal clearance; ADEMEX and the Hong Kong randomized trial showed that higher prescribed peritoneal small-solute clearance did not improve survival. [1–7]

1. Adequacy has changed meaning

Older PD practice often reduced adequacy to whether a calculated small-solute threshold was reached. Contemporary ISPD practice deliberately broadens the question: is the treatment achieving the person’s clinical and life goals with acceptable symptoms, volume status, nutrition, biochemical control, residual kidney function and treatment burden? Weekly Kt/V remains useful, but only as one element of that assessment. [1–3]

Table 7.2 — Five domains of adequate PD.

Domain	What success looks like	What a Kt/V cannot tell you
Symptoms / function	Acceptable energy, appetite, cognition, sleep and daily function	Whether the person feels well
Volume / sodium	Stable weight trend, acceptable BP, no clinically important congestion	Whether sodium balance is controlled
Biochemistry	Acceptable potassium, bicarbonate and other relevant trends	Whether every metabolic target is controlled
Nutrition	No unexplained progressive nutritional deterioration	Cause of low albumin or poor intake
Life goals / burden	Treatment fits agreed priorities with tolerable workload	Whether the prescription is worth its burden

BEDSIDE TRANSLATION Document adequacy as a sentence, not a number: “Clinically well with controlled volume and biochemistry, meaningful RKF, and small-solute clearance consistent with current goals” is more useful than “Kt/V 1.82.”

2. Kt/V urea: useful, specific and limited

Figure 7.3 — What weekly Kt/V urea actually measures.

Kt/V is a dimensionless index of urea clearance scaled to urea distribution volume. It is deliberately a small-solute metric; it does not directly measure sodium balance, middle-molecule removal or quality of life.

Kt/V expresses urea clearance (K) accumulated over time (t) relative to the urea distribution volume (V), usually approximated by total body water. In PD, the weekly value usually includes a peritoneal component and, when urine is present, a renal component. The arithmetic is convenient; the biology is more complex.

Table 7.3 — What Kt/V captures and what it misses.

Captures reasonably	Captures indirectly/poorly	Does not define
Urea removal	Overall nitrogenous-solute exposure	Volume status
Change in small-solute dose	Some consequence of missed treatments	Sodium balance
Renal + peritoneal urea-clearance accounting	Body-size effect through V	Middle molecules / protein-bound solutes
Longitudinal trend when collection is valid	Some prescription response	Symptoms, nutrition or quality of life

THRESHOLD DISCIPLINE The ISPD 2019 update concluded that there is no demonstrated survival advantage in targeting weekly Kt/V above 1.70. The lower limit remains uncertain; evidence supporting ≥1.7 in anuric adults is weak. Use 1.7 as a decision-support threshold—not as a claim that 1.69 is treatment failure and 1.71 proves success. [2]

3. Why “more Kt/V” stopped being the goal

Two landmark randomized experiences changed PD adequacy thinking. In ADEMEX, increasing peritoneal urea/creatinine clearance did not improve survival. In the Hong Kong randomized study, higher Kt/V targets did not produce a clear survival advantage over lower target ranges, although very low clearance was clinically undesirable. These data weaken the assumption that every extra increment of peritoneal urea clearance improves patient outcome. [5,6]

Table 7.4 — Landmark evidence that reshaped adequacy.

Study	Key comparison	Clinical lesson
CANUSA reanalysis	Residual GFR and urine output vs peritoneal clearance	Renal and peritoneal clearance are not outcome-equivalent
ADEMEX	Higher peritoneal clearance vs conventional CAPD	Increasing peritoneal small-solute dose did not improve survival
Hong Kong randomized Kt/V study	Three total Kt/V target ranges	Higher targets did not clearly improve survival; avoid interpreting “more” as automatically better

DO NOT OVER-DIALYZE THE NUMBER If the patient is clinically well, euvolemic and biochemically controlled, increasing exchanges solely to move Kt/V farther above an already acceptable value can add glucose exposure, connections and burden without proven survival benefit.

4. Total clearance: additive arithmetic, unequal biology

Figure 7.2 — Total measured clearance has two components.

Renal and peritoneal urea clearances can be added mathematically. CANUSA reanalysis demonstrated that their clinical associations are not equivalent.

The traditional total Kt/V is calculated by adding peritoneal and renal urea-clearance components. That arithmetic is valid for urea accounting, but it must not imply biological equivalence. Residual kidneys provide continuous water, sodium and a broader spectrum of solute clearance plus endocrine and metabolic functions. [4,7]

Table 7.5 — Residual kidney clearance versus peritoneal clearance.

Feature	Residual kidneys	Peritoneal dialysis
Timing	Continuous native function	Programmed exchanges/cycles
Water/sodium	Physiologic urine excretion	Osmotic ultrafiltration + dialysate sodium removal
Solute spectrum	Broad native filtration/secretion	Membrane- and dwell-dependent
Treatment burden	No additional exchange burden	Requires connections, dialysate and time
Outcome association	Consistently strong observational association	Higher small-solute dose above conventional range has not shown survival benefit

5. How to measure peritoneal small-solute clearance

Figure 7.5 — The adequacy collection chain.

Collection integrity is part of the test. A mathematically precise calculation from an incomplete collection is still wrong.

Peritoneal clearance assessment requires complete collection of drained dialysate over the defined period, accurate total drain volume, representative dialysate sampling, and an appropriate plasma urea measurement. Automated-PD collections must account for the complete cycler and daytime prescription. A missed bag or unrecorded drain can create a false low result.

Table 7.6 — Peritoneal clearance collection checklist.

Check	Why it matters	Failure phenotype
All dialysate captured	Defines total solute mass removed	Low measured clearance if drains omitted
Accurate total drain volume	Volume is part of clearance calculation	Dose error from guessed volumes
Representative mixed sample	Concentration must represent all effluent	Biased D/P concentration
Correct collection duration	Converts clearance to weekly value	Wrong time scaling
Plasma sample appropriately timed	Provides denominator concentration	Spurious result when clinical state changed markedly
Prescription actually delivered	Measurement should reflect real therapy	“Adequate prescription” but inadequate delivery

MEASUREMENT RULE When a result is surprising, verify the collection before changing the prescription. Measurement error is a treatable cause of “low adequacy.”

6. The denominator V: the hidden source of error

Kt/V is normalized to an estimate of urea distribution volume. Anthropometric formulas are approximations, and edema, obesity, amputation, severe cachexia and unusual body composition can make V uncertain. The denominator therefore contributes error even when dialysate collection is perfect.

Table 7.7 — Situations in which V can mislead.

Situation	Why interpretation becomes difficult	Clinical safeguard
Marked obesity	Adipose tissue contains less water than lean tissue	Do not equate total body weight with urea distribution volume
Edema/overhydration	Measured body water is temporarily expanded	Interpret clearance alongside volume assessment
Severe cachexia	Anthropometric equations may fit poorly	Use trends and clinical state
Amputation / unusual habitus	Standard equations assume usual anatomy	Document method and avoid false precision

NUMERICAL HUMILITY Do not manufacture precision from an uncertain V. If the number conflicts with the patient, inspect the measurement assumptions before declaring treatment failure.

7. Creatinine clearance: complementary, not a second adequacy target to chase

Creatinine equilibrates more slowly than urea and is more sensitive to dwell time and peritoneal transport phenotype. Historically, weekly creatinine clearance normalized to 1.73 m² was used alongside Kt/V. Contemporary ISPD guidance does not restore the old concept of chasing multiple mandatory clearance targets; creatinine clearance is most useful when it helps explain discordant physiology or when renal GFR is being estimated from urinary urea and creatinine clearances. [1–3]

Table 7.8 — Kt/V versus creatinine clearance.

Feature	Weekly Kt/V urea	Creatinine clearance
Solute	Urea	Creatinine
Normalization	Urea distribution volume V	Often body surface area
Transport sensitivity	Rapid equilibration	More dwell/transport dependent
Current role	Primary small-solute dose metric	Complementary physiologic/renal-function information
Major trap	Equating target achievement with total adequacy	Chasing an old numeric target without clinical reason

8. Residual kidney function: the most valuable clearance you do not prescribe

Figure 7.4 — Why residual kidney function matters beyond urea.

Residual kidneys add continuous urine, sodium and broad-solute clearance. Their value is not reproduced by an equal numerical increment in peritoneal Kt/V.

Residual kidney function (RKF) is consistently associated with better outcomes in PD. CANUSA reanalysis showed that increments in residual GFR and urine volume were associated with lower mortality risk, whereas equivalent changes in peritoneal creatinine clearance were not. This does not prove that preserving RKF itself causes all of the survival advantage, but it establishes RKF as a major clinical prognostic and treatment variable. [4]

Table 7.9 — Clinical benefits associated with preserved RKF.

Domain	Why RKF helps
Volume	Urine output buffers fluid and sodium intake
Solute control	Adds continuous urea/creatinine and broader toxin removal
Phosphate/potassium	Native excretion can reduce biochemical burden
Nutrition	Allows lower dialysis burden and less glucose exposure in suitable patients
Quality of life	May permit incremental prescriptions and fewer exchanges
Outcomes	Observational studies consistently associate RKF with survival

9. Measuring residual kidney function correctly

For routine PD practice, RKF should be estimated from a timed urine collection using the mean of renal urea clearance and renal creatinine clearance. Creatinine clearance alone overestimates true GFR because of tubular secretion; urea clearance alone tends to underestimate it. Their mean is a practical compromise supported by PD guidance and physiology. [7]

Table 7.10 — Timed urine collection: what is required.

Element	Required information	Common error
Collection interval	Usually a complete 24-h urine collection	Missed voids
Urine volume	Measured, not estimated	Using diary volume without actual collection
Urine urea + creatinine	Laboratory concentrations	Wrong units
Plasma urea + creatinine	Representative blood sample	Non-contemporaneous sample during instability
Calculation	Renal urea and creatinine clearances, then mean	Using creatinine clearance alone as GFR

PRACTICE POINT Chen, Perl and Teitelbaum recommend measuring RKF from the mean 24-h urinary creatinine and urea clearances, ideally on a regular longitudinal schedule such as quarterly while clinically meaningful RKF persists. Local programs may individualize frequency. [7]

10. Urine volume is not the same as RKF — but it matters

Urine volume and solute clearance answer different questions. A patient can produce urine with little solute clearance, and a modest urine volume may still carry meaningful sodium and water excretion. CANUSA reanalysis found a strong association between urine volume and survival, reinforcing that urine should be tracked separately from renal Kt/V. [4]

Table 7.11 — Urine volume versus renal clearance.

Measure	Tells you	Does not tell you
24-h urine volume	Water excretion and practical volume reserve	Exact solute clearance
Renal Kt/V	Urea-clearance contribution	Sodium removal or total kidney function
Mean urea/creatinine clearance	Practical RKF estimate	All tubular/endocrine functions

11. Preserving RKF: protect a clinical asset

Figure 7.6 — Residual kidney function preservation is a system.

The goal is not maximal blood pressure reduction or maximal ultrafiltration; it is stable perfusion, euvolemia, infection prevention and avoidance of preventable kidney insults.

Table 7.12 — RKF-preservation strategy.

Strategy	Physiologic logic	Clinical caution
Avoid volume depletion	Preserves kidney perfusion	Do not tolerate chronic overload to “protect urine”
Control BP appropriately	Limits vascular/glomerular injury	Avoid symptomatic hypotension
RAAS blockade when otherwise appropriate	May preserve RKF and has cardiovascular indications	Individualize potassium/BP tolerance
Loop diuretics when responsive	Maintain urine volume and sodium excretion	Do not mistake diuresis for preserved GFR
Prevent/treat peritonitis	Inflammation/illness can accelerate RKF loss	Peritonitis is also a technique threat
Judicious nephrotoxin/contrast exposure	Avoid preventable kidney injury	Do not withhold essential diagnostics reflexively
Incremental prescription when suitable	Avoid unnecessary glucose/burden while kidneys contribute	Requires active surveillance and escalation

BALANCE RULE Preserving RKF does not mean keeping the patient wet. Chronic congestion is harmful. The target is euvolemia without recurrent intravascular depletion.

12. What accelerates RKF decline?

The evidence for individual predictors is mostly observational. A 2023 systematic review/meta-analysis identified associations between RKF loss/decline and factors including diabetes, peritonitis, proteinuria and higher systolic blood pressure; such associations do not establish that every factor is directly modifiable or causal. [10]

Table 7.13 — RKF decline: modifiable and non-modifiable signals.

Signal	Interpretation	Action
Peritonitis / intercurrent illness	Inflammatory/hemodynamic insult	Prevent; treat promptly; reassess RKF afterward
Repeated hypotension / dehydration	Potential renal hypoperfusion	Review UF, diuretics and BP regimen
Uncontrolled hypertension	Vascular/kidney injury risk	Optimize BP without overcorrection
Nephrotoxic exposure	Potential direct injury	Risk-benefit review and monitoring
Diabetes / proteinuria	Higher-risk phenotype	Optimize disease-specific care
Time on dialysis	Expected biological decline	Plan prescription escalation rather than blame the patient

13. Falling RKF is a prescription-changing event

Flowchart 7.3 — Falling residual kidney function.

A falling urine or renal-clearance trend changes the total kidney-replacement prescription even when every PD setting is unchanged.

The most common “silent underdialysis” scenario is an unchanged PD prescription in a patient whose kidneys are providing progressively less clearance and volume control. Total measured Kt/V may fall, but the more clinically important signals may be edema, hyperphosphatemia, rising potassium, worsening appetite or increased symptom burden.

Table 7.14 — What changes when RKF falls.

Domain	Likely direction	What to reassess
Total Kt/V	Falls if PD unchanged	Need for more peritoneal clearance
Urine volume	Often falls	Sodium/fluid prescription
Potassium/phosphate	May worsen	Diet, medications and dialysis contribution
Treatment burden needed	Often rises	CAPD/APD architecture and patient priorities
Glucose exposure	May rise if UF support increases	Use dwell/agent strategy rather than reflex hypertonicity

14. Low Kt/V: diagnose before escalating

Flowchart 7.2 — Low measured weekly Kt/V.

The correct response to a low number begins with collection validity, delivery and RKF trend—not automatic addition of exchanges.

Table 7.15 — Low Kt/V differential.

Cause	Clue	Corrective direction
Incomplete dialysate collection	Missing bags / implausible drain total	Repeat valid collection
Incomplete urine collection	Urine volume inconsistent with usual output	Repeat renal component
Missed exchanges / cycler lost time	Treatment log discrepancy	Fix delivery problem
Catheter/drain retention	Poor drain, alarms, retained volume	Mechanical pathway
Loss of RKF	Falling urine or renal clearance	Increase peritoneal support as needed
Prescription insufficient for body size/transport	Valid delivery but persistent low clearance	Adjust volume, dwell, exchanges or modality

15. “Kt/V is fine but the patient is not”

A satisfactory small-solute number does not neutralize a clinical problem. Congestion, poor sodium balance, malnutrition, recurrent peritonitis, severe treatment burden, constipation, access dysfunction or non-uremic disease can all coexist with an apparently acceptable Kt/V.

Table 7.16 — Adequate number, inadequate patient.

Problem	Why Kt/V may remain acceptable	Next question
Edema / hypertension	Urea clearance can be adequate while sodium removal is poor	Volume/sodium mechanism?
Poor appetite / weight loss	Inflammation, depression, GI disease or dialysis burden	Is this uremia or another illness?
Fatigue	Anemia, sleep, heart failure, depression, infection	What competing diagnosis exists?
Hyperphosphatemia	Phosphate behaves differently from urea	Diet/binder/RKF/dwell strategy?
High burden	Clearance achieved at unacceptable workload	Can goals be met with a different architecture?

CLINICAL RULE Never use a Kt/V result to dismiss a symptom. Use it to narrow the differential.

16. “The patient feels well but Kt/V is below target”

This situation requires equal caution in the opposite direction. First verify collection and delivery. Then assess RKF, volume, potassium, bicarbonate, nutrition and symptom trajectory. In an anuric adult, a persistently low weekly Kt/V deserves active prescription review because the evidence supporting ≥1.7 is weak but remains the principal guideline-based small-solute floor. The absence of symptoms is not proof that a sustained clearance shortfall is harmless. [2]

Table 7.17 — Low Kt/V with few symptoms: disciplined response.

Step	Action
1	Repeat/validate the collection if unexpected
2	Confirm treatment delivery and catheter function
3	Measure RKF accurately
4	Review volume, potassium, bicarbonate, nutrition and trajectory
5	If true shortfall persists, increase peritoneal support using physiology
6	Recheck after the change; avoid endless escalation if another modality better meets goals

17. The anuric patient: peritoneal dialysis must carry the whole load

Once RKF is absent, the peritoneal prescription becomes responsible for essentially all dialytic solute and fluid support. The margin for missed treatments, poor drains and prolonged low-UF dwells becomes smaller. This is the context in which the weekly Kt/V ≥1.7 practice point is most relevant, but clinical volume and biochemical targets remain equally important. [2]

Table 7.18 — Anuric PD checklist.

Domain	Question
Small solutes	Is weekly peritoneal Kt/V consistently adequate by a valid collection?
Volume	Is net UF plus intake strategy maintaining euvolemia?
Sodium	Is sodium removal sufficient, especially with short APD dwells?
Potassium/acid-base	Are biochemical targets stable?
Phosphate/nutrition	Is dietary/prescription strategy adequate?
Delivery	Are missed cycles or drainage problems reducing dose?
Burden	Is achieving targets requiring an unsustainable prescription?

18. Incremental PD: adequacy requires an escalation contract

Incremental PD deliberately uses less peritoneal dialysis while RKF contributes meaningfully. Contemporary comparative evidence is heterogeneous but generally supports feasibility in selected patients without a clear mortality penalty. The safety condition is not the starting dose; it is active monitoring with pre-defined escalation when RKF, symptoms, volume or biochemical goals change. [11]

Table 7.19 — Incremental PD: what must be monitored.

Signal	Escalation trigger concept
Urine/RKF	Meaningful decline from the patient’s prior contribution
Symptoms	New uremic symptom burden
Volume	Worsening sodium/water control
Biochemistry	Persistent deterioration despite medical therapy
Clearance	True total small-solute shortfall
Life situation	Prescription no longer fits goals or support resources

19. Adequacy assessment algorithm

Flowchart 7.1 — Is PD adequate for this patient?

The algorithm starts with the clinical state, then verifies delivery, RKF and small-solute clearance before any prescription change.

Table 7.20 — One-minute adequacy synthesis.

If you see…	Think…	Do now…
Well + euvolemic + stable labs + meaningful urine	Current total support may be appropriate	Maintain; preserve RKF; avoid unnecessary burden
Low Kt/V only	Measurement/delivery problem possible	Validate collection and logs
Falling urine + edema + same prescription	Loss of RKF	Recalculate total support and adjust PD
Good Kt/V + edema	Volume/sodium problem	Treat volume physiology, not urea number
Anuric + low Kt/V	True peritoneal dose shortfall until proven otherwise	Verify then intensify or reassess modality
High prescription burden + good clinical state	Possible overtreatment relative to goals	Reconsider architecture; do not sacrifice safety

20. Clinical pearls

RKF is not “bonus dialysis”; it is a major clinical organ function that changes the prescription.
A stable PD order becomes a smaller total kidney-replacement treatment when urine and RKF fall.
Urine volume and renal clearance should both be followed; they answer different questions.
An unexpectedly low Kt/V is a collection-quality problem until the collection is proven valid.
Good urea clearance does not prove good sodium removal.
If the patient is clinically well, do not add glucose-rich exchanges solely to make an already acceptable number look larger.
In an anuric patient, missed treatments and drainage failure have greater clinical consequences because there is no kidney reserve.
The best RKF-preservation strategy is balanced: avoid congestion and avoid recurrent hypovolemia.

21. Common pitfalls — and the correction

Table 7.21 — High-frequency adequacy errors.

Pitfall	Why it fails	Correction
Calling Kt/V “adequacy”	Collapses a multidimensional outcome into one solute	Use a dashboard
Treating 1.69 and 1.71 as different clinical worlds	False precision around low-certainty threshold	Use trend + clinical context
Adding renal and peritoneal clearance as biologically equal	CANUSA contradicts equivalence	Value RKF separately
Escalating after one low collection	Collection may be incomplete	Validate before prescribing
Using urine volume as GFR	Volume and solute clearance differ	Measure timed urea/creatinine clearance
Using creatinine clearance alone for RKF	Tubular secretion overestimates GFR	Use mean renal urea + creatinine clearance
Preserving urine by tolerating overload	Congestion is harmful	Target euvolemia
Ignoring falling RKF in incremental PD	Total support silently shrinks	Define escalation triggers

22. Mini-cases: decisions, not trivia

Case 1 — The “adequate” congested patient

A patient has weekly Kt/V 1.84 but progressive edema, rising BP and poor daytime UF.

BEST NEXT STEP Do not increase dialysis because the number is “too low”; it is not low. Diagnose a sodium/volume problem: intake, urine decline, dwell/transport mismatch, osmotic strategy and mechanical function. Chapter 8 develops the full volume pathway.

Case 2 — Sudden low Kt/V

A previously stable CAPD patient has weekly Kt/V 1.42 on one collection but feels unchanged. The drain log shows one exchange was discarded before sampling.

BEST NEXT STEP The collection is invalid. Repeat a complete collection before changing the prescription.

Case 3 — Incremental PD and falling urine

A patient on a low-burden incremental regimen loses substantial urine over three months and develops hyperphosphatemia and fatigue.

BEST NEXT STEP The same PD prescription now provides less total support. Confirm RKF decline, assess volume/biochemistry, and escalate the peritoneal prescription according to the failing targets.

Case 4 — Anuric APD with low clearance

An anuric patient completes nocturnal APD but has persistently low weekly Kt/V. Cycler logs show many very short cycles and repeated drain alarms.

BEST NEXT STEP Delivered therapy is not equivalent to the written prescription. Correct drainage/catheter and cycle-time problems before simply adding more cycles.

Case 5 — Good numbers, severe fatigue

Kt/V and volume status are acceptable, but the patient has marked fatigue and dyspnoea.

BEST NEXT STEP Do not label symptoms “uremia” automatically. Evaluate anemia, cardiac disease, sleep, infection, depression and other competing diagnoses.

Case 6 — Preserving RKF badly

A patient with useful urine is repeatedly driven to very low post-dialysis weight using hypertonic glucose because edema is feared. Urine falls rapidly.

BEST NEXT STEP Reassess true volume state and avoid recurrent intravascular depletion. RKF preservation requires euvolemia—not aggressive dehydration.

23. Active recall

MUST MEMORIZE

Q: What does weekly Kt/V urea measure? A: Small-solute urea clearance relative to urea distribution volume over one week.

Q: What is the principal ISPD small-solute practice-point threshold for anuric adults? A: Weekly Kt/V approximately 1.7; evidence supporting the lower limit is weak.

Q: How should RKF be estimated from urine? A: Mean of timed renal urea and creatinine clearances.

Q: Why not use creatinine clearance alone for RKF? A: Tubular secretion causes creatinine clearance to overestimate true GFR.

Q: Does higher peritoneal Kt/V above conventional levels improve survival? A: Randomized evidence has not demonstrated a survival advantage.

Q: What did CANUSA reanalysis teach? A: Residual GFR/urine were strongly associated with outcome; peritoneal clearance was not equivalent.

Q: Can a patient have adequate Kt/V and poor volume control? A: Yes. Solute clearance and sodium/water balance are distinct.

Q: What should you do before changing a prescription for one low Kt/V? A: Validate collection and treatment delivery.

MUST REASON

Why can loss of 24-h urine make an unchanged PD prescription clinically inadequate?
Why might adding APD cycles worsen clearance if each dwell becomes too short?
Why can aggressive ultrafiltration threaten RKF?
Why can an obese patient have an apparently low Kt/V despite reasonable clinical dialysis?
Why is an anuric patient less tolerant of missed exchanges or catheter dysfunction?

USE AS REFERENCE

Exact local adequacy-collection protocol and sample handling.
Anthropometric equation used to estimate V.
Unit-specific interval for repeat clearance/RKF measurement.
Detailed volume-management and UF-failure pathways in Chapter 8.
Prescription optimization by CAPD/APD architecture in Chapter 9.

24. Flashcards: active recall

1. Q: Adequacy in one phrase? A: Patient-centred goals + volume + biochemistry + nutrition + RKF + appropriate clearance.

2. Q: Kt/V is a measure of? A: Urea small-solute clearance scaled to V.

3. Q: Best routine RKF clearance estimate? A: Mean urinary urea and creatinine clearance.

4. Q: Urine volume equals GFR? A: No.

5. Q: ADEMEX lesson? A: More peritoneal small-solute clearance did not improve survival.

6. Q: CANUSA reanalysis lesson? A: Kidney clearance/urine mattered more than peritoneal clearance.

7. Q: Unexpected low Kt/V: first move? A: Check collection validity and delivered treatment.

8. Q: Good Kt/V + edema? A: Volume/sodium pathway.

9. Q: Anuria changes what? A: PD must provide essentially all dialytic solute and fluid support.

10. Q: Incremental PD safety requirement? A: Active RKF/clinical monitoring with escalation triggers.

11. Q: RKF preservation volume target? A: Euvolemia — neither chronic overload nor recurrent depletion.

12. Q: Can Kt/V dismiss symptoms? A: No.

13. Q: Why track urine separately? A: Water/sodium excretion has value beyond urea clearance.

14. Q: Creatinine clearance alone for RKF? A: Avoid; use mean with urea clearance.

15. Q: Higher Kt/V always better? A: No evidence of survival benefit above conventional target range.

16. Q: True low Kt/V after verification? A: Adjust the mechanism: volume, dwell, exchanges, total time or modality.

25. Rapid troubleshooting table

Table 7.22 — Adequacy problem → likely mechanism → next step.

Problem	Likely mechanism(s)	Next step
Low total Kt/V	Collection error, missed therapy, RKF loss, insufficient prescription	Validate → delivery → RKF → prescription
Low renal component	Incomplete urine or true RKF decline	Repeat if doubtful; assess reversible insults
Good Kt/V + edema	Sodium/volume problem	Chapter 8 pathway
Good Kt/V + symptoms	Non-uremic cause or other dialysis domain	Broaden differential
Anuric + poor biochemistry	Peritoneal support insufficient or delivery problem	Verify and intensify/reassess modality
Incremental PD + falling urine	Total support shrinking	Escalate according to failing targets
High burden + excellent numbers	Possible unnecessary dose intensity	Revisit patient goals and minimal effective prescription

26. Final revision sheet

TEN TAKE-HOME RULES 1) Adequacy is a clinical dashboard. 2) Kt/V measures urea clearance, not the whole patient. 3) Higher peritoneal clearance above conventional targets has not improved survival in randomized trials. 4) RKF has disproportionate clinical value. 5) Measure RKF from the mean urinary urea + creatinine clearance. 6) Track urine volume separately. 7) Validate a low clearance collection before escalating treatment. 8) Good Kt/V does not prove good sodium/volume control. 9) Falling RKF changes the total prescription. 10) Incremental PD is safe only with an escalation plan.

Table 7.23 — Final revision grid.

Core concept	Remember
Adequacy	Symptoms + function + volume + biochemistry + nutrition + life goals + RKF + clearance
Weekly Kt/V	Small-solute metric; ≥1.7 is a low-certainty practice point, especially relevant when anuric
Landmark evidence	CANUSA: RKF/urine matter; ADEMEX/Hong Kong: more peritoneal clearance not necessarily better
RKF measurement	Timed urine; mean renal urea + creatinine clearance
Low Kt/V	Collection → delivery → catheter/drain → RKF → prescription
Preservation	Euvolemia, hemodynamic stability, infection prevention, nephrotoxin discipline
Anuria	No kidney reserve: peritoneal prescription carries the full dialytic load

FINAL MENTAL MODEL Patient state → volume/sodium → delivered treatment → urine/RKF → small-solute measurement → identify failing domain → correct mechanism → verify response. The number supports the clinical decision; it does not replace it.

Rapid oral viva

Explain weekly Kt/V urea to a nephrology fellow without using the word “adequacy.”
Why are renal and peritoneal clearances mathematically additive but clinically unequal?
Walk through your response to a weekly Kt/V of 1.45 in a previously stable patient.
How do you measure residual kidney function and why is urine volume also recorded separately?
Give the differential for edema in a patient whose weekly Kt/V is 1.9.
What changes in your adequacy framework when a patient becomes anuric?

SCOPE BOUNDARY This chapter teaches adequacy, clearance measurement and RKF. Detailed sodium/volume management and ultrafiltration failure are developed in Chapter 8; CAPD/APD prescription optimization is developed in Chapter 9.

27. Selected authoritative references

1. Brown EA, Blake PG, Boudville N, et al. International Society for Peritoneal Dialysis practice recommendations: Prescribing high-quality goal-directed peritoneal dialysis. Perit Dial Int. 2020;40(3):244–253. https://doi.org/10.1177/0896860819895364. PMID: 32063219.

2. Boudville N, de Moraes TP. 2005 Guidelines on targets for solute and fluid removal in adults being treated with chronic peritoneal dialysis: 2019 update of the literature and revision of recommendations. Perit Dial Int. 2020;40(3):254–260. https://doi.org/10.1177/0896860819898307. PMID: 32048566.

3. Teitelbaum I, Glickman J, Neu A, et al. KDOQI US Commentary on the 2020 ISPD Practice Recommendations for Prescribing High-Quality Goal-Directed Peritoneal Dialysis. Am J Kidney Dis. 2021;77(2):157–171. https://doi.org/10.1053/j.ajkd.2020.09.010. PMID: 33341315.

4. Bargman JM, Thorpe KE, Churchill DN. Relative contribution of residual renal function and peritoneal clearance to adequacy of dialysis: a reanalysis of the CANUSA study. J Am Soc Nephrol. 2001;12(10):2158–2162. https://doi.org/10.1681/ASN.V12102158. PMID: 11562415.

5. Paniagua R, Amato D, Vonesh E, et al. Effects of increased peritoneal clearances on mortality rates in peritoneal dialysis: ADEMEX, a prospective, randomized, controlled trial. J Am Soc Nephrol. 2002;13(5):1307–1320. https://doi.org/10.1681/ASN.V1351307. PMID: 11961019.

6. Lo WK, Ho YW, Li CS, et al. Effect of Kt/V on survival and clinical outcome in CAPD patients in a randomized prospective study. Kidney Int. 2003;64(2):649–656. https://doi.org/10.1046/j.1523-1755.2003.00098.x. PMID: 12846762.

7. Chen CH, Perl J, Teitelbaum I. Prescribing high-quality peritoneal dialysis: The role of preserving residual kidney function. Perit Dial Int. 2020;40(3):274–281. https://doi.org/10.1177/0896860819893821. PMID: 32063188.

8. Morelle J, Stachowska-Pietka J, Öberg C, et al. ISPD recommendations for the evaluation of peritoneal membrane dysfunction in adults: classification, measurement, interpretation and rationale for intervention. Perit Dial Int. 2021;41(4):352–372. https://doi.org/10.1177/0896860820982218.

9. Borràs Sans M, Ponz Clemente E, Rodríguez Carmona A, et al. Clinical guideline on adequacy and prescription of peritoneal dialysis. Nefrologia (Engl Ed). 2024;44 Suppl 1:1–27. https://doi.org/10.1016/j.nefroe.2024.09.001. PMID: 39341764.

10. Zhou D, Lei H, Wu S, et al. Influencing factors for residual kidney function in incident peritoneal dialysis patients: a systematic review and meta-analysis. Ren Fail. 2023;45(2):2286328. https://doi.org/10.1080/0886022X.2023.2286328. PMID: 38036948.

11. Xu S, Wu W, Cheng J. Comparison of outcomes of incremental vs. standard peritoneal dialysis: a systematic review and meta-analysis. BMC Nephrol. 2024;25:308. https://doi.org/10.1186/s12882-024-03669-w. PMID: 39285336.

12. Wang AY. The John F. Maher Award Recipient Lecture 2006. The ‘heart’ of peritoneal dialysis: residual renal function. Perit Dial Int. 2007;27(2):116–24. PMID: 17299143.

13. Li PKT, Chow KM, Cho Y, et al. ISPD peritonitis guideline recommendations: 2022 update on prevention and treatment. Perit Dial Int. 2022;42(2):110–153. https://doi.org/10.1177/08968608221080586.

14. Davies SJ. Peritoneal dialysis—current status and future challenges. Nat Rev Nephrol. 2013;9:399–408. https://doi.org/10.1038/nrneph.2013.100.

SOURCE NOTE Guideline status and contemporary adequacy/RKF evidence were checked 2 September 2026. Exact collection procedures, V-estimation method, laboratory units, monitoring frequency and reimbursement-linked thresholds can vary by jurisdiction and program; local protocols should define operational details without replacing the patient-centred ISPD framework.