Weill Cornell Medicine Care Discover Teach
Weill Cornell Medicine — Pediatric Critical Care Medicine

Continuous Renal Replacement Therapy (CRRT) Clearance

All calculations should be independently verified prior to clinical use. These calculators are intended to supplement, not replace, clinical judgment.

Calculate the theoretical clearance of a continuous renal replacement therapy (CRRT) circuit from blood flow rate, ultrafiltration rate, replacement rate, and solute protein binding.

Pre-filter configuration only. This calculation applies to pre-filter replacement configurations only. It does not apply to post-filter replacement or diafiltration methods. Clearances are theoretical and should be confirmed by other means. Medication dosing should not be based solely on the clearance calculated here.
mL/min
mL/hr
L/hr
%

Note: BFR, UFR, and RR use different units — enter each in the units shown. Conversion to mL/min is handled internally.

Cuf/Cp
mL/min

The clearance of a CRRT system applies the same principle as measured creatinine clearance — the ultrafiltrate is the “urine” in this context. The units for BFR, UFR, and RR differ on most CRRT machines and are first converted to mL/min before calculation.

The ultrafiltrate concentration (expressed as a fraction of plasma concentration) accounts for protein binding and the dilutional effect of pre-filter replacement fluid:

Cuf / Cp = (1 − ProBind) × BFRmin ÷ (BFRmin + RRmin)

Total clearance is then:

Clearance = (Cuf / Cp) × (UFRmin + RRmin)

The actual plasma concentration value is not required — only the ratio of ultrafiltrate to plasma concentration matters, and the units cancel. Protein binding reduces effective clearance: a solute that is 90% protein bound (ProBind = 90%) will have markedly lower clearance than a freely filtered solute (ProBind = 0%).

As a special case, when the replacement rate is zero, clearance equals the ultrafiltration rate converted to mL/min.

References

  1. Churchwell MD, Mueller BA. Selected pharmacokinetic issues in patients with chronic kidney disease and patients on renal replacement therapies. Adv Chronic Kidney Dis. 2010;17(5):427–432.
  2. Aronoff GR, Bennett WM, Berns JS, et al. Drug Prescribing in Renal Failure: Dosing Guidelines for Adults and Children. 5th ed. American College of Physicians; 2007.
  3. Bellomo R, Ronco C, Mehta RL. Nomenclature for continuous renal replacement therapies. Am J Kidney Dis. 1996;28(5 Suppl 3):S2–S7.