118 eGFR MDRD
The glomerular filtration rate (GFR) is the volume of blood plasma that the kidneys' filters (glomeruli) clean per minute. It is the best overall measure of kidney function. Measuring GFR directly is laborious, so it is estimated (eGFR) from serum creatinine, age and sex using equations such as MDRD or the newer CKD-EPI. The result is expressed per 1.73 m² of body surface area. A healthy young adult has an eGFR of about 100–120 mL/min/1.73 m²; values below 60 for more than three months define chronic kidney disease.
The MDRD equation
The MDRD equation was developed in 1999 from 1628 patients with chronic kidney disease. The version used with standardised (IDMS-traceable) creatinine is:
eGFR = 175 × Scr−1.154 × age−0.203 × 0.742 (if female)
Here Scr is serum creatinine in mg/dL (µmol/L ÷ 88.4). The original equation included a race coefficient; current practice no longer uses race. MDRD is reasonably accurate when GFR is below 60 but underestimates normal and near-normal GFR. For this reason the CKD-EPI equations, updated in 2021 without race, are now recommended by KDIGO for routine reporting. Adding cystatin C improves accuracy when creatinine is unreliable.
When eGFR can be misleading
- Unusual muscle mass: athletes and bodybuilders (eGFR underestimated), amputees, frail elderly people, malnutrition or muscle-wasting disease (eGFR overestimated)
- High intake of meat or creatine supplements shortly before the test
- Rapidly changing kidney function (acute kidney injury): equations assume a stable state
- Pregnancy, extremes of body size, children (special equations are used)
- Medicines that block creatinine secretion (trimethoprim, cimetidine, some HIV drugs) raise creatinine without real loss of GFR
Why GFR matters
Chronic kidney disease affects about one in ten adults worldwide and is often silent until advanced. Lower eGFR and higher albuminuria independently increase the risk of cardiovascular events, kidney failure and death. eGFR also guides the dosing of many medicines and the use of contrast agents. Early detection allows treatment that slows decline: blood pressure and glucose control, ACE inhibitors or angiotensin receptor blockers, SGLT2 inhibitors, and avoiding nephrotoxic drugs such as NSAIDs.
An eGFR below 60 should be repeated within 3 months, together with a urine albumin-to-creatinine ratio. Discuss with your doctor which medicines need dose adjustment. People with diabetes, hypertension, heart disease or a family history of kidney disease should have eGFR and urine albumin checked regularly.
if eGFR falls suddenly, or if reduced kidney function comes with very little urine, swelling, breathlessness, confusion or a high potassium level.
References
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2024;105(4S):S117–S314. doi:10.1016/j.kint.2023.10.018
- Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med. 1999;130(6):461–470. PMID: 10075613
- Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737–1749. doi:10.1056/NEJMoa2102953
This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.
Published on 7 May 2024