- Enter age, sex, height, and weight (toggle cm/in and kg/lb to match your records) — these set Watson total body water (V) and DuBois body-surface area (BSA).
- Pick the serum solute unit: enter serum urea as BUN (mg/dL) or as urea (mmol/L). Dialysate and urine urea must be entered in the same unit as serum.
- From the 24-hour dialysate collection, enter total drained volume (L/day), dialysate urea, and dialysate creatinine.
- Enter serum urea and serum creatinine.
- Residual renal function is optional: if there is a 24-hour urine collection, enter urine volume, urine urea, and urine creatinine. Leave all three blank for an anuric patient — the renal contribution is then zero.
- The result shows total weekly Kt/V, total weekly CrCl (L/1.73 m²), the peritoneal vs renal breakdown, V and BSA, and a verdict against the ISPD 2020 targets.
All computation runs in your browser; no values are stored or transmitted.
When to Use
Use this tool to quantify the small-solute clearance a peritoneal dialysis (PD) prescription is delivering. It combines the peritoneal contribution (from a 24-hour dialysate collection) with the residual renal contribution (from a paired 24-hour urine collection) and reports two complementary measures: total weekly Kt/V for urea and total weekly creatinine clearance normalized to 1.73 m². Both are referenced to the ISPD 2020 framework, in which total weekly Kt/V ≥ 1.7 remains the recommended minimum floor.
Appropriate population
Stable, established PD patients (CAPD or APD) undergoing a routine adequacy assessment with a complete 24-hour dialysate collection. Paired same-day serum, dialysate, and (if any urine output remains) urine samples should be drawn. Residual renal function, when present, is a major contributor and must be included for an accurate total.
When NOT to rely on it
The result is only as good as the collection: incomplete dialysate or urine drainage understates clearance. Do not assess adequacy during peritonitis, the first weeks after PD initiation, or any unstable state. ISPD 2020 explicitly de-emphasizes fixed small-solute targets in favour of person-centred, goal-directed care — a number above target does not guarantee a well patient, and small-solute clearance is not a substitute for assessing volume status, nutrition, symptoms, and quality of life. Kt/V and CrCl can diverge (especially as residual renal function falls); interpret both.
Pearls & Pitfalls
Residual renal function counts twice over
Native kidney clearance contributes to both total Kt/V and total CrCl and is weighted heavily — preserving it (ACE inhibitor/ARB where appropriate, avoiding nephrotoxins and volume depletion, biocompatible solutions) often does more for adequacy than escalating the dialysis prescription. As urine output falls, the peritoneal prescription must do more to hold the same total.
Keep the urea units consistent
Serum, dialysate, and urine urea must all be expressed in the same unit, because Kt/V uses their ratio (dialysate-or-urine urea ÷ serum urea), which is unit-free. This tool lets you enter serum urea as BUN (mg/dL) or urea (mmol/L) and applies the same choice to the fluid samples. Creatinine ratios are likewise unit-free, so mg/dL vs µmol/L cancels as long as numerator and denominator match.
Pitfalls
(1) Residual renal CrCl is conventionally the average of urea and creatinine clearance (the renal tubule secretes creatinine, overstating GFR; urea is reabsorbed, understating it) — this tool applies that averaging. (2) Total CrCl must be normalized to 1.73 m² BSA; a large patient with a "good" raw CrCl can be below target once indexed. (3) An incomplete collection is the commonest cause of a falsely low result. (4) Hitting ≥1.7 is a floor, not a goal — under ISPD 2020, manage to the patient, not the number.
Why Use It
Inadequate small-solute clearance on PD is associated with uraemic symptoms and, historically, worse outcomes, while an objective adequacy measure lets you adjust the prescription rationally — dwell volume, number of exchanges, dwell time, or transport-tailored APD/CAPD regimens. Computing Kt/V and CrCl together, with the residual renal contribution made explicit, shows where the clearance is coming from and how vulnerable the patient is to losing native function. ISPD 2020 reframes the target as a minimum safeguard within a broader, person-centred prescription; this calculator supplies that quantitative floor while leaving the clinical goals to judgment.
Peritoneal Dialysis Adequacy — Weekly Kt/V + Creatinine Clearance
Enter anthropometrics, the 24-hour dialysate collection, paired serum, and (if any urine output remains) the 24-hour urine collection. The tool reports total weekly Kt/V and total weekly CrCl (normalized to 1.73 m²), with the peritoneal/renal breakdown, against ISPD 2020 targets. Leave the renal block blank for an anuric patient.
Patient
Serum
24-hour dialysate
Residual renal — optional (leave blank if anuric)
⚕ Peritoneal weekly Kt/V = (D/P urea × dialysate L/day × 7) ÷ V; renal weekly Kt/V = (U/P urea × urine L/day × 7) ÷ V; total = sum (target ≥ 1.7). Peritoneal weekly CrCl = D/P creatinine × dialysate L/day × 7; residual renal CrCl = mean of urine creatinine and urine urea clearances × 7; total weekly CrCl normalized ×(1.73 ÷ BSA), target ≥ 45 L/1.73 m². V = Watson TBW; BSA = DuBois. Urea ratios are unit-free, so dialysate/urine urea must share the serum-urea unit (BUN mg/dL or urea mmol/L). Educational aid for clinicians — not a substitute for clinical judgment, complete collections, or person-centred ISPD 2020 care. Source: Brown EA et al. ISPD 2020. Perit Dial Int. 2020;40(3):244–253.
Next Steps
Use the result to support — not replace — clinical judgment.
- If total weekly Kt/V is below 1.7, first confirm the collection was complete, then consider increasing dwell volume, adding exchanges, or optimizing dwell time to transport status (PET-guided APD vs CAPD).
- Make preserving residual renal function a priority — review nephrotoxin exposure, avoid volume depletion, and use an ACE inhibitor/ARB where appropriate; native clearance contributes heavily to both totals.
- Interpret Kt/V and CrCl together; they can diverge, and ISPD 2020 treats ≥1.7 as a floor within a broader, person-centred prescription, not a stand-alone goal.
- Assess the patient, not just the number — volume status, blood pressure, nutrition (nPCR/SGA), uraemic symptoms, and quality of life — and trend serial adequacy studies rather than acting on one result.
- Escalate to the PD team / nephrology when targets are unmet despite a maximized prescription, when residual function is falling, or when clinical adequacy is in doubt.
Evidence & References
Formula & Equations
| Quantity | Equation |
|---|---|
| Watson total body water — men (V, L) | 2.447 − 0.09516 × age + 0.1074 × height(cm) + 0.3362 × weight(kg) |
| Watson total body water — women (V, L) | −2.097 + 0.1069 × height(cm) + 0.2466 × weight(kg) |
| Body-surface area (DuBois, m²) | 0.007184 × height(cm)^0.725 × weight(kg)^0.425 |
| Peritoneal weekly Kt/V | (dialysate urea ÷ serum urea) × drain volume(L/day) × 7 ÷ V |
| Renal weekly Kt/V | (urine urea ÷ serum urea) × urine volume(L/day) × 7 ÷ V |
| Total weekly Kt/V | peritoneal Kt/V + renal Kt/V (target ≥ 1.7) |
| Peritoneal weekly CrCl (L/week) | (dialysate Cr ÷ serum Cr) × drain volume(L/day) × 7 |
| Renal creatinine clearance (L/day) | (urine Cr ÷ serum Cr) × urine volume(L/day) |
| Renal urea clearance (L/day) | (urine urea ÷ serum urea) × urine volume(L/day) |
| Residual renal CrCl (L/day) | mean of renal creatinine clearance and renal urea clearance (× 7 for weekly) |
| Total weekly CrCl, normalized | (peritoneal + renal weekly CrCl) × (1.73 ÷ BSA) (target ≥ 45 L/1.73 m²) |
| Unit handling | If serum urea entered as BUN (mg/dL), urea (mmol/L) = BUN ÷ 2.8. Urea and creatinine appear only as ratios (fluid ÷ serum), which are unit-free as long as both share a unit. Weight (kg) = lb ÷ 2.2046; height (cm) = in × 2.54. |
Why residual renal CrCl is averaged
The native kidney secretes creatinine (overestimating GFR) and reabsorbs urea (underestimating GFR). By long-standing PD-adequacy convention (K/DOQI), residual renal creatinine clearance is taken as the arithmetic mean of the measured creatinine and urea clearances to reduce this bias. The peritoneal CrCl is not averaged — it uses dialysate creatinine directly.
Targets
| Measure | Threshold | Interpretation |
|---|---|---|
| Total weekly Kt/V (urea) | ≥ 1.7 | ISPD 2020 recommended minimum floor for combined peritoneal + renal small-solute clearance |
| Total weekly CrCl | ≥ 45 L/1.73 m² | Historical K/DOQI creatinine-clearance target; ISPD 2020 de-emphasizes fixed CrCl targets but still references it |
ISPD 2020 shifted from rigid small-solute targets toward person-centred, goal-directed prescribing: ≥1.7 is a safeguard, not a goal, and clearance numbers must be interpreted alongside volume status, nutrition, symptoms, and quality of life. A complete 24-hour dialysate (and urine) collection is essential — incomplete collection is the commonest cause of a falsely low result.
Evidence & References
The 2020 ISPD practice recommendations reframe PD adequacy around high-quality, goal-directed care for the individual rather than fixed small-solute clearance numbers, while retaining total weekly Kt/V ≥ 1.7 as a minimum. Watson's equations (1980) supply total body water (V) for the Kt/V denominator, and the DuBois formula (1916) supplies body-surface area for normalizing creatinine clearance to 1.73 m².
- 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.
- Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr. 1980;33(1):27–39.
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17(6 Pt 2):863–871.
