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    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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