Creatinine

  • Non-protein end product of creatinine metabolism.
  • Formed from skeletal muscle and excreted in constant amounts.
  • Completely filtered by kidney (marker of GFR)
  • Production proportional to muscle mass
  • Relatively unaffected by diet, exercise or urine volume
  • More sensitive test of renal damage.  Elevation of levels almost exclusively secondary to renal impairment
  • Clearance is an excellent indicator of kidney efficiency in clearing creatinine
    • Clearance levels become abnormal when >50% of nephron units have become damaged

Causes of increased serum creatinine

  1. Renal impairment (>50% nephrons affected) – any cause of renal failure, basically
    • Pre-renal
      • Decreased perfusion to the kidney
      • Dehydration, hypovolaemia, shock
    • Renal
      • Intrinsic renal lesion
      • Nephrotoxic drugs
    • Post renal obstruction
  2. Nephrotoxic drugs
    • NSAID, aspirin, indomethacin
    • Ampicillin, rifampicin, cephalosporin, aminoglycosides
    • Frusemide, Thiazides, acetazolamide, mannitol
    • Lithium, iron, lead, copper, gold
  3. Metabolic
    • Acromegaly
    • Hyperthyroidism
    • Very large muscle mass (athletes) (without renal compromise)
    • NOT affected by dietary protein intake
  4. Fictitious
    • Interfere with colorimetric analysis (Glucose, fructose, ascorbic acid)

Causes of a Decreased Creatinine

  • Pregnancy
  • Conditions characterised by muscle wasting
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