eGFR in women: normal values and pregnancy

The eGFR value estimates how many millilitres of blood your kidneys filter per minute, scaled to a standard body surface area of 1.73 square metres. The e stands for estimated. The laboratory measures your creatinine, a waste product of muscle tissue that the kidneys remove from the blood, and puts it together with your age and your sex into the 2021 CKD-EPI equation; some laboratories also report the newer EKFC equation.

That your sex appears in the equation is not an assumption about women's kidneys. It corrects for muscle mass, because creatinine comes from muscle and women on average carry less muscle than men. Without that correction results would sit structurally skewed.

There is a flip side. In a slight woman with little muscle the value can read too favourably: the kidneys then filter less than the number suggests. CKD-EPI and EKFC share that limitation, because both start from the same creatinine. Cystatin C, a protein that comes from almost all body cells, bypasses muscle mass and gives a fairer picture in that case.

During pregnancy kidney filtration rises by 40 to 50 percent, and the equations were never validated for that situation. An eGFR value from a pregnancy check is therefore hard to read. Creatinine actually falls in that period, so a value that looks normal outside pregnancy can be on the high side during it. Always have such a result interpreted by your midwife or doctor.

After a pregnancy with pre-eclampsia the kidney deserves lasting attention. The risk of later kidney damage and of cardiovascular disease is higher then. In that follow-up the amount of albumin in the urine weighs heavily, because damage can show there while the eGFR is still normal.

Outside those two situations the ordinary reading applies. A value of 90 or above is normal, 60 to 89 is called mildly reduced, and the value falls from about age forty by roughly 1 ml/min per year. Around seventy a value between 70 and 80 is very common. Chronic kidney damage only exists once the value stays under 60 for at least three months or protein is found in the urine; one result under 60 is a reason to repeat and not a diagnosis.

Around menopause nothing specific changes in kidney function. The gradual age-related decline continues, and what strains the kidneys most in that phase is rising blood pressure and disturbed blood sugar.

Outside pregnancy the eGFR is usually calculated alongside routine blood work, as soon as creatinine is measured. With diabetes, high blood pressure or kidney disease in the family that is especially useful, and after pre-eclampsia kidney function belongs in long-term follow-up.

If you are pregnant, say so at the draw, because the equation does not apply then and the result belongs with your midwife or doctor.

Never read a one-off low value as a diagnosis. Only three months of the same result counts, and a repeat measurement on an ordinary day, well hydrated and not right after hard exertion, is the first step. Ask whether protein in the urine was measured too.

If your doctor doubts the number fits your build, cystatin C offers a way out. Always discuss an abnormal result with your doctor in person.