Skip to Main Content

  1. Glomerular filtration rate (GFR)

    1. Best overall measure of kidney function

    2. Best estimated using inulin clearance, but this is rarely done in practice

  2. Serum creatinine

    1. Level varies with age, sex, race or ethnic group, muscle mass, diet, nutritional status

    2. The relationship between creatinine and GFR varies inversely and exponentially, so that early, small changes in serum creatinine may reflect clinically significant decreases in GFR.

      1. A 50-year-old white man with a baseline serum creatinine of 1.0 mg/dL has a GFR of 80 mL/min/1.73 m2; if his creatinine increases by 50% to 1.5 mg/dL, his GFR drops to 50 mL/min/1.73 m2.

      2. If his baseline serum creatinine is 4.0 mg/dL, his GFR is about 16 mL/min/1.73 m2; if his creatinine increases by 50% to 6.0 mg/dL, his GFR is about 10 mL/min/1.73 m2.

    3. An increase in creatinine, without a change in GFR, may be seen due to inhibition of tubular secretion of creatinine by certain drugs, eg, trimethoprim, cimetidine, and pyrimethamine (pseudo-AKI).

  3. Estimates of GFR

    1. Measured creatinine and urea clearance

      1. Creatinine is filtered by glomeruli and secreted by the proximal tubule, so creatinine clearance overestimates GFR. Urea is filtered by glomeruli, reabsorbed by the proximal tubule and collecting ducts and secreted by loop of Henle; urea clearance tends to underestimate GFR.

      2. May be calculated with a 24-hour urine collection. The average of creatinine and urea clearances may better estimate GFR.

    2. Cockcroft-Gault formula (multiply by 0.85 for women):

      image

      1. Does not adjust for body surface area

      2. Does not accurately estimate kidney function in those with normal GFRs, obese patients, or adults over 70 years.

      3. Used preferentially by pharmacists for adjusting dosages of medications

    3. Modification of Diet in Renal Disease Study Equation (MDRD) study equation:

      image

      1. Online calculator available: http://www.kidney.org/professionals/kdoqi/gfr_calculator.cfm

      2. Does not accurately estimate kidney function in those with AKI, normal GFRs, obese patients, or adults over 70 years

      3. Overall, more accurate and more commonly used than Cockcroft-Gault formula or 24-hour urine measurement of creatinine clearance.

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.

  • Create a Free Profile