eGFR, weight and blood sugar: what counts?

eGFR comes from an equation rather than a measurement. CKD-EPI uses your creatinine, age and sex. The result is normalised to a body surface area of 1.73 square metres.

That normalisation deserves attention at a high body weight. The value says what your filtration would be at an average build. For drug dosing the non-normalised value sometimes counts. In a large body that difference is anything but small.

Some labs also report an EKFC result. Two equations, the same starting point, a slightly different number.

In excess weight and in early diabetes the kidney often filters harder than normal. That is called hyperfiltration. On paper it produces a nice high value. In reality the filter units work under raised pressure. Over time that can actually damage the kidney.

An eGFR above 90 is therefore no proof of healthy kidneys. Above that many labs simply report greater than 90. Protein in the urine often shows damage earlier than eGFR does.

The 60 to 89 band counts as mildly reduced. Below 60 only matters once it persists for three months. The value also falls on its own with age, about 1 ml/min per year after forty.

With raised weight or disturbed blood sugar, kidney function belongs in the picture. eGFR is usually calculated automatically alongside creatinine. Ask about protein in the urine too, as it completes the picture.

During substantial weight loss many things change at once. Muscle mass falls and protein intake shifts. Both affect creatinine and therefore the calculated value. So compare measurements taken under comparable conditions where possible.

If the result does not fit your situation, cystatin C can help. It does not depend on muscle mass. Discuss any abnormal value with your doctor.