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Blood Sciences Test


Calculated result using the CKD-EPI formula

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Special Instructions

A variety of methods have been used. All are based on serum creatinine estimations.

Although the Cockcroft-Gault formula is widely used, it was developed to permit estimation of CrCl, not of GFR.

The best validated method comes from the MDRD Study data (Ann Int Med 130:461-70, 877-84, 1999). The study derived a number of equations. The abbreviated, or four-variable equation includes age, sex, creatinine, and race (black or not black). Adding more variables (albumin, urea) adds little to accuracy.

It is important to be aware of the limitations of these equations (more info on eGFR from the UK CKD eGuide):

  • Accuracy – even for the MDRD equation, which is the best there is, the confidence limits are wide. 90% of values are within 30% of the true value; 98% within 50%.
  • Extremes – none of the methods for estimating GFR without actual measurements of it are likely to be accurate in extreme examples of low muscle mass, or other unusual circumstances.
  • Stability – for all methods, [creat] must not be changing quickly.
  • Systematic errors – MDRD is better at low GFRs.
  • Age – the Schartz or Counahan Barrat equation (requires height) should be used in children.
  • Race, different equations – more info

Most UK labs now report eGFR when returning creatinine values. When available, these values should be more accurate than calculations performed by you, as they should incorporate lab-specific correction factors. If not, here are some resources:

The UK Renal Association Website – www.renal.org/eGFR

Online calculator from nephron.com offers a simple abbreviated MDRD, and has a useful menu of alternatives including quaint US units and also Cockroft-Gault. Take care to set units for [creat] correctly.



Reference Range

Only calculated for patient’s greater than 18 years with values less than 60 reported

Test Usage

Estimation of glomerular filtration rate



Specimen Labelling Procedure
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