- Select the BUN unit to match your lab report (mg/dL or urea mmol/L). Switching the unit clears the BUN fields.
- Enter the predialysis BUN drawn just before the current dialysis session.
- Enter the postdialysis BUN from the previous session — the value at the end of the run that began the gap you are measuring.
- Enter the interdialytic interval in hours between those two draws (e.g. 44 h for a short gap, 68 h for the long weekend gap on a thrice-weekly schedule).
- The result shows the nPCR (nPNA) in g/kg/day, the interdialytic BUN rise, the target band, and an interpretation with a recommended action.
All computation runs in your browser; no values are stored or transmitted. Valid only in metabolically stable patients at steady state.
When to Use
Use nPCR (normalized protein catabolic rate, also termed nPNA — normalized protein nitrogen appearance) to estimate dietary protein intake in a stable maintenance hemodialysis patient. At neutral nitrogen balance, urea generation between dialysis sessions is driven almost entirely by protein catabolism, so the rate at which BUN rises across the interdialytic interval is a quantitative surrogate for protein intake. nPCR is one of the routine nutritional monitoring parameters recommended alongside serum albumin and a structured nutrition assessment, and is best trended monthly with the urea-kinetic adequacy panel.
Appropriate population
Adult maintenance hemodialysis patients who are metabolically stable and at steady state — not acutely ill, not septic, not on high-dose steroids, and without large recent changes in residual kidney function. Use the BUN draws that bracket a single interdialytic interval: the predialysis BUN of the current session and the postdialysis BUN of the immediately preceding session.
When NOT to rely on it
Do not interpret nPCR during acute illness, hypercatabolism, or any non-steady state — the protein-intake equivalence holds only at neutral nitrogen balance. Significant residual renal urea clearance removes urea between sessions and lowers the apparent BUN rise, underestimating nPCR unless residual clearance is accounted for. This bedside interdialytic-rise method does not include residual renal function or a separate volume term, so it is an approximation. nPCR is a surrogate, not a measured intake — always correlate with serum albumin, weight trend, and a formal nutrition/SGA assessment.
Pearls & Pitfalls
Get the two draws right
The BUN rise must span one interdialytic interval: the predialysis BUN of the current session minus the postdialysis BUN at the end of the previous session. Drawing both as predialysis values, or mixing sessions, breaks the calculation. The interval (commonly 44 h or the 68 h long gap) must match the two draws used.
Normalize to the right weight
nPCR is normalized to body weight derived from the urea distribution volume (V), not to actual edematous or volume-overloaded weight. Normalizing to a fluid-overloaded weight will artificially lower nPCR and can mislabel an adequately-nourished patient as protein-depleted. Trend the value rather than reacting to a single result.
Pitfalls
(1) Only valid at metabolic steady state — acute illness, sepsis, or steroid-driven hypercatabolism inflates urea generation independent of intake. (2) Significant residual renal function clears urea between sessions and underestimates nPCR unless corrected. (3) nPCR equals protein intake only at neutral nitrogen balance; in net anabolism or catabolism the two diverge. (4) It is a surrogate — confirm nutritional status with serum albumin, weight, and a formal SGA/dietitian assessment, not nPCR alone.
Why Use It
Protein-energy wasting is common in maintenance dialysis and is strongly associated with mortality. A persistently low nPCR (<1.0 g/kg/day) is an early, objective signal of inadequate protein intake that often precedes a fall in serum albumin, prompting earlier dietitian referral and intervention. Conversely a high nPCR (>1.4 g/kg/day) flags excessive protein intake or a hypercatabolic state. Because it is computed from the routine pre/post-dialysis BUN already drawn for adequacy monitoring, nPCR adds a quantitative nutritional metric at essentially no extra cost — best used trended over time alongside albumin and clinical assessment, not as a stand-alone diagnosis.
nPCR / nPNA Calculator — Interdialytic BUN Rise Method
Enter the predialysis BUN, the previous session's postdialysis BUN, and the interdialytic interval to estimate the normalized protein catabolic rate (nPCR / nPNA) as a surrogate for dietary protein intake. Use the BUN unit toggle if your lab reports urea in mmol/L.
⚕ nPCR (g/kg/day) = 0.22 + [0.036 × (interdialytic BUN rise in mg/dL) × 24] ÷ (interdialytic interval in hours), where rise = predialysis BUN (current) − postdialysis BUN (previous session). Urea mmol/L → BUN mg/dL via × 2.8. Valid only in metabolically STABLE hemodialysis patients at steady state; assumes negligible residual renal urea clearance and neutral nitrogen balance. Normalize to V-derived dry weight, not edematous weight. A surrogate for protein intake — correlate with serum albumin and nutrition assessment. Source: Daugirdas JT. J Am Soc Nephrol. 1993;4(5):1205–1213; KDOQI 2020 Nutrition Update.
Next Steps
Use the result to support — not replace — clinical judgment.
- Interpret the value against the 1.0–1.2 g/kg/day target and the bands in the Evidence section below, in the context of the full clinical picture.
- Trend nPCR monthly alongside serum albumin, dry-weight trend, and Kt/V rather than acting on a single result; confirm unexpected values before changing management.
- For a low nPCR (<1.0 g/kg/day): refer to the renal dietitian, assess for protein-energy wasting, review dialysis adequacy and appetite, and consider oral nutritional supplementation.
- For a high nPCR (>1.4 g/kg/day): assess for excessive protein intake versus a hypercatabolic or non-steady state, and reconcile with adequacy and phosphate/potassium control.
- Refer or escalate when results are discordant with albumin, the SGA, or the clinical picture — and discuss dietary goals with the patient.
Evidence & References
Formula & Equations
| Quantity | Equation |
|---|---|
| nPCR / nPNA (g/kg/day) | 0.22 + [0.036 × (interdialytic BUN rise, mg/dL) × 24] ÷ (interdialytic interval, hours) |
| Interdialytic BUN rise | predialysis BUN (current session) − postdialysis BUN (previous session) |
| BUN ⇄ urea conversion | BUN (mg/dL) = urea (mmol/L) × 2.8 |
| Worked example | rise 30 mg/dL over 44 h → 0.22 + (0.036 × 30 × 24 ÷ 44) = 0.22 + 0.589 = 0.81 g/kg/day |
Interpretation bands
| nPCR (g/kg/day) | Interpretation |
|---|---|
| < 1.0 | Suggests inadequate protein intake / possible protein-energy wasting — dietitian referral |
| 1.0–1.2 | Adequate protein intake (KDOQI target range) |
| 1.2–1.4 | Upper-acceptable; reasonable intake, monitor phosphate/potassium |
| > 1.4 | High protein intake or hypercatabolism — assess steady state and dietary load |
nPCR equals protein intake only at neutral nitrogen balance and in a metabolically stable patient. The bedside interdialytic-rise equation assumes negligible residual renal urea clearance; significant residual function will underestimate nPCR. Normalize to V-derived dry weight, not edematous weight.
Evidence & References
nPCR (nPNA) derives from urea kinetic modeling: at steady state and neutral nitrogen balance, urea nitrogen appearance between dialysis sessions reflects protein catabolism and therefore protein intake. The simplified interdialytic-rise formula implemented here is the widely used bedside approximation; more rigorous single-pool (Daugirdas–Depner) two-point models additionally incorporate Kt/V, the urea distribution volume, and residual renal clearance. KDOQI recommends a dietary protein intake of roughly 1.0–1.2 g/kg/day for clinically stable maintenance hemodialysis patients and lists nPNA among the parameters for routine nutritional monitoring.
- Daugirdas JT. Second generation logarithmic estimates of single-pool variable volume Kt/V: an analysis of error. J Am Soc Nephrol. 1993;4(5):1205–1213.
- Depner TA, Daugirdas JT. Equations for normalized protein catabolic rate based on two-point modeling of hemodialysis urea kinetics. J Am Soc Nephrol. 1996;7(5):780–785.
- Ikizler TA, Burrowes JD, Byham-Gray LD, et al. KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update. Am J Kidney Dis. 2020;76(3 Suppl 1):S1–S107.
