Assessment of elevated creatinine

Serum creatinine concentration is maintained by the balance between its generation and excretion by the kidneys. Levels are affected by factors that influence the generation, glomerular filtration, and tubular secretion of serum creatinine. There is considerable variation in the excretion of creatinine based on individual patient factors and the time and method of testing. Since creatinine is generated in a steady manner and can be measured very simply from blood samples, it has become a useful test to estimate glomerular filtration rate (GFR), which is a measurement of kidney function.

The reference range of serum creatinine is:

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  60 to 110 micromol/L (0.7 to 1.2 mg/dL) for men
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  45 to 90 micromol/L (0.5 to 1.0 mg/dL) for women.
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• Creatinine is an amino acid breakdown product of creatine and phosphocreatine and is found almost exclusively (90%) in skeletal muscle. It is generated at a fairly constant rate and freely filtered through the glomerulus. In addition, 5% to 10% of creatinine is secreted by the proximal tubules.
  Typically, serum creatinine rises from 0.5 to 1 mg/day to 1 to 2 mg/day in acute kidney injury (AKI), but it can exceed 5 mg/day in patients with severe rhabdomyolysis, due to massive breakdown of skeletal muscle. In patients with acute and rapidly progressive glomerulonephritis, 90% of renal function can be lost within weeks to months owing to glomerular destruction and this manifests as a 'galloping' rise in serum creatinine.
• • eGFR = 107.3/SCr/Q for people aged ≥2 years and <40 years
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    eGFR = (107.3/SCr/Q) x 0.988 (age-40) for people aged >40 years.
  • Mild increases in in-hospital serum creatinine have been associated with short-term mortality, progression to CKD, and accelerated progression to end-stage renal disease. They present a higher long-term mortality risk, especially in those with partial renal recovery. 
  •   They may also have prognostic significance for estimating the risk of death in many disease states: for example, an increase of only urea levels and a combination of increased urea and creatinine levels, but not isolated elevated creatinine, were independent risk factors of death from acute coronary syndromes.
  • Differntiation:
• Glomerulonephritis
• Diabetic nephropathy
•  Systemic vasculitis
• Nephrotoxic medications/fenofibrate-associated creatinine increase

Radiotherapy
Endogenous nephrotoxins
Renal artery stenosis

•  Traumatic renal infarction
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