Nephrology Book

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Creatinine ClearanceAka: Glomerular Filtration Rate, GFR, CrCl, Cockcroft-Gault, Modification of Diet in Renal Disease, MDRD

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  1. Indications
    1. Creatinine clearance estimates GFR
  2. Normal Creatinine Clearance
    1. Men
      1. Average: 120 ml/min/1.73 m2 (+/-25) or 175 Liters/day
      2. Range: 97-137 ml/min/1.73 m2 (0.93-1.32 ml/sec/m2 IU)
    2. Women
      1. Average: 95 ml/min/1.73 m2 (+/-20) or 135 Liters/day
      2. Range: 88-128 ml/min/1.73 m2 (0.85-1.23 ml/sec/m2 IU)
  3. Calculation: Cockcroft-Gault formula for GFR estimate
    1. Indications: Stable kidney function
      1. Older patients
      2. General screening
    2. Male GFR = (140 - age) x (weight) / (sCr x 72)
    3. Female GFR = (140 - age) x (weight) x 0.85 / (sCr x 72)
    4. Annotation
      1. Where GFR is Glomerular Filtration Rate in ml/min
      2. Where age is in years
      3. Where weight is Lean Body Mass in kilograms
      4. Where sCr is Serum Creatinine in mg/dl
    5. Efficacy
      1. As accurate as 24 hour urine in most cases
      2. Exceptions: See 24 hour CrCl indications below
    6. Resources: GFR Calculator
      1. http://www.kidney.org/kls/professionals/
  4. Calculation: Abbreviated MDRD Study Equation
    1. Indications: Chronic Kidney Disease, stable function
      1. Middle aged patients
      2. Black patients
      3. Diabetic Nephropathy
      4. Status-post kidney transplant
    2. Efficacy
      1. More accurate than Cockroft-Gault in CRF
        1. Levey (1999) Ann Intern Med 130:461
      2. Underestimates GFR in the absence of kidney disease
        1. Rule (2004) Ann Intern Med 141:929
    3. Formula: GFR = 186 x (sCr)^-1.154 x (age)^-0.203
      1. Where sCr is raised by power of -1.154
      2. Where age is raised by power of -0.203
    4. Modifiers
      1. Female: Multiply GFR by 0.742
      2. Black: Multiply GFR by 1.210
    5. Annotation
      1. Where GFR=Glomerular filtration rate ml/min/1.73 m2
      2. Where sCr is Serum Creatinine in mg/dl
  5. Calculation: 24 hour Creatinine Clearance
    1. Previously considered gold standard GFR evaluation
      1. Now thought to be less accurate than calculations (see above) due to flawed collection
    2. Indications
      1. Pregnancy
      2. Severely underweight or overweight
      3. Very young and very old
      4. Malnutrition
      5. Skeletal muscle disorders, paraplegia, quadriplegia
    3. Formula
      1. CrCl = (uCr x uV) / (sCr x 1440)
    4. Annotation
      1. Where CrCl is Creatinine clearance in ml/min
      2. Where uCr is Urine Creatinine in mg/dl
      3. Where sCr is Serum Creatinine in mg/dl
      4. Where uV is 24 hour urine volume in ml
      5. Where 1440 represents number of minutes in 24 hours
    5. Indications (where calculation above is inaccurate)
      1. Altered protein intake
        1. Vegetarian diet
        2. Creatine Supplementation
      2. Altered muscle mass
        1. Malnutrition or muscle wasting
        2. Amputation
  6. Increased
    1. Pregnancy
    2. Exercise
  7. Decreased
    1. Renal insufficiency
    2. Advanced age
      1. Normal GFR is 125 ml/min/1.73 m2 at age 30 years
      2. GFR decreases by 1 ml/min/year over age 30 years
    3. Inadequate urine specimen collection
      1. See Urine Creatinine for judging adequacy
    4. Medications (Decrease tubular secretion of Creatinine)
      1. Cimetidine
      2. Procainamide
      3. Antibiotics
      4. Quinidine
  8. Pitfalls
    1. Creatinine clearance (by 24 hour urine) is overestimated at decreased GFR
      1. As GFR decreases, secreted Creatinine makes up larger percentage of total Urine Creatinine
      2. Consider pre-medicating the 24 hour Urine Collection
        1. Give Cimetidine or Trimethoprim for 2 days prior to 24 hour Urine Collection

Glomerular Filtration Rate (C0017654)

Definition (MSH)The volume of water filtered out of plasma through glomerular capillary walls into Bowman's capsules per unit of time. It is considered to be equivalent to INULIN clearance.
Definition (CSP)rate at which plasma is filtered by the glomerular filtration membrane into Bowman's space; determined by the permeabiliy of the membrane, hydrostatic pressure in the glomerular capillaries and Bowman's space, and the colloid osmotic pressure exerted by the proteins of the capillary plasma.
ConceptsOrgan or Tissue Function (T042) , Diagnostic Procedure (T060)
EnglishGFR, Glomerular Filtration Rate, Glomerular Filtration Rates
Spanishtasa de filtración glomerular, tasa de filtracion glomerular
CreditsDerived from the NIH UMLS (Unified Medical Language System)


CREATININE CLEARANCE QUANTITATIVE TRAIT LOCUS (C1846718)

ConceptsDisease or Syndrome (T047)
EnglishCRCL, CREATININE CLEARANCE QUANTITATIVE TRAIT LOCUS
CreditsDerived from the NIH UMLS (Unified Medical Language System)



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