Analysis

Formula estimation of glomerular filtration rate: have we gone wrong?

BMJ 2007; 334 doi: 10.1136/bmj.39226.400694.80 (Published 7 June 2007)
Cite this as: BMJ 2007;334:1198

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  1. Paul D Giles, consultant chemical pathologist1,
  2. David A Fitzmaurice, professor2
  1. 1Department of Biochemistry, Manor Hospital, Walsall WS2 9PS
  2. 2Department of Primary Care and General Practice, University of Birmingham, Birmingham B15 2TT
  1. Correspondence to: P D Giles paul.giles{at}walsallhospitals.nhs.uk

    Paul D Giles and David A Fitzmaurice argue that the introduction of estimated glomerular filtration rate to screen for chronic kidney disease in primary care will lead to pressure on specialist services and create patient anxiety without clear proof of benefit

    Chronic kidney disease is a public health problem worldwide.1 The estimated prevalence of established renal failure is around 1400 per million in the United States and more than 600 per million in the United Kingdom. Patients with chronic kidney disease have increased risk of cardiovascular disease. A test that reliably detects early kidney disease could help minimise cardiovascular disease and renal failure.

    Estimating glomerular filtration rate

    The best known function of the kidneys is plasma filtration—measured by the glomerular filtration rate (GFR). Many of the kidney's functions are related to GFR (box 1). Inulin clearance and modern isotopic methods are not practical for measuring GFR in routine practice. Creatinine based tests are used instead but have several disadvantages. Creatinine clearance involves timed urine collection and is prone to error. Measuring serum creatinine is easier but this test cannot detect early kidney disease.2 Routine reporting of estimated GFR using formulas based on serum creatinine concentration plus age, sex, and racial group was first advocated in the US and has now been recommended in many other countries.

    Box 1 Functions of the kidneys related to glomerular filtration rate3

    • Excretion of nitrogenous waste, sodium, free water, potassium, phosphate, and water soluble medicines (such as digoxin and gentamicin)

    • Control of blood pressure

    • Acid-base balance

    • Secretion of erythropoietin

    • Hydroxylation of vitamin D1 (activation)

    • Gluconeogenesis in the fasting state

    • Catabolism of peptide hormones (including insulin)

    In the UK the second part of the national service framework for renal services,4 published in 2005, required clinical biochemistry laboratories to develop automatic reporting of formula based GFR estimates. In 2006 the quality and outcomes framework5 asked primary care to …

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