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Best Tests December 2005

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Estimated Glomerular Filtration rate (eGFR)

Even a small decline in renal function is associated with increased health risk (e.g. CVD risk). Early detection and management has the potential for significant health benefits. Serum creatinine levels are influenced by gender, muscle mass and activity. Up to 25% of patients with “normal” serum creatinine have early stage chronic kidney disease (CKD).
Many laboratories report an estimated GFR (eGFR) whenever a serum creatinine is requested. An eGFR based on the Modified Diet in Renal Disease (MDRD) equation does not need the patient’s weight and correlates well with true GFR in most patients with a degree of renal impairment. However, there are several limitations to consider when interpreting these results:

  • The MDRD formula is not reliable in some settings (e.g. dialysis, acute renal failure, severe liver disease, people with low protein intake and children).
  • It has not yet been validated in Māori, Pacific Island or Asian populations.
  • A value of > 60 when the plasma creatinine is normal may be unreliable.
  • A value of 60-90 may indicate mild kidney damage and further investigation is indicated if haematuria, proteinuria or hypertension are present.
  • A value of 30-59 indicates a moderate decline in kidney function and the need for regular monitoring. ACE inhibitors for proteinuria or specialist referral may be appropriate.
  • A value of ≤ 30 indicates possibly severe CKD and the need for specialist referral.
  • The eGFR (MDRD) is not used for adjustment of drug doses, such as for allopurinol. In these situations the bpacnz creatinine clearance calculator or tables based on the Cockcroft & Gault equation is more appropriate.

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