last updated 21-11-2024

Creatinine clearance

 

The excretory function of the kidneys can change dramatically due to age or disease. It is therefore important for clinicians to be able to determine a particular patient’s renal function before dosing a renally eliminated drug.

Creatinine is a breakdown product of muscle. The rate of breakdown is usually fairly steady except in situations of extreme stress or fasting.

Serum creatinine is nearly 100% cleared via the kidneys and as such, it’s clearance can serve as a measurement of the Glomerular Filtration Rate (GFR).

Estimating creatinine clearances is typically performed in one of three ways:

 

  1. Nowadays the estimated GFR (eGFR) using Modification of Diet in Renal Disease (MDRD) is mostly used.

    GFR=32788 · [SCr] -1.154 x age -0,203 · constant

    • constant = 1 for men, 0.742 for women
    • [SCr] is serum creatinine (in µmol/L)
  2. 24 hour urine collection using the volume over 24 hours.

    CrCl = [CrU] · VU24 / [SCr] · 24hr · 60min

    • Urinve volume over 24 hours = VU24
    • concentration of the creatinine in the urine = [CrU]
    • concentration of serum creatinine = [SCr]:
  3. An older method for the estimation of the creatinine clearance is the Cockcroft-Gault formula

    CrCl = (140 – age) · Kg · constant / [SCr]

    • using the patients age (in years) = age
    • patient’s weight = Kg
    • concentration of serum creatinine = [SCr]
    • constant = 1.23 for men, 1.04 for women

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