eGFR Test: What Your Kidney Function Number Really Means

If a screening report has ever come back with a line reading "eGFR" and a number beside it, that number is one of the most useful things on the page. It estimates how well your kidneys are filtering — and because kidney disease is typically silent until it is advanced, it is often the first hint that anything is wrong. This guide explains what the number means, what the ranges are, and what should and should not worry you.

What is eGFR?

Your kidneys contain around a million tiny filtering units called glomeruli. The glomerular filtration rate is the volume of blood they clear of waste each minute, reported in millilitres per minute per 1.73 square metres of body surface area — written as mL/min/1.73m².

Measuring that rate directly is possible but slow and impractical for routine care. Instead the laboratory estimates it, which is what the "e" stands for. The estimate comes from your blood creatinine level, adjusted for age and sex.

Creatinine is a waste product from normal muscle turnover. Healthy kidneys clear it steadily, so creatinine rising in the blood suggests filtration is falling. The calculation turns that relationship into a single number that is far easier to interpret than creatinine on its own.

eGFR normal range and what each band means

Kidney function is described in stages, from G1 through G5. The bands below are the internationally used categories:

The most commonly misread band is G2. An eGFR of 75 often causes real alarm, when in most people it simply reflects normal age-related decline. Filtration falls gradually from around the age of 40 in almost everyone. What matters is whether it is falling faster than expected, and whether anything else on the report is abnormal.

Why eGFR alone does not diagnose kidney disease

Chronic kidney disease has two components in its definition: reduced filtration, or evidence of kidney damage — and either must persist for at least three months. That three-month rule exists because a single reading can be thrown off by things that have nothing to do with long-term kidney health.

Things that can temporarily lower an eGFR reading include:

• Dehydration — one of the most frequent causes of a one-off low result.
• A large meat meal shortly before the test — dietary creatine raises creatinine for a period afterwards.
• Intense exercise in the preceding day or two — muscle turnover pushes creatinine up.
• Certain medicines — trimethoprim and cimetidine among them, which block creatinine secretion without harming the kidney itself.

The reverse is also true, and matters more than most people expect. Because the estimate assumes an average relationship between muscle mass and creatinine, it reads differently in bodies that sit outside that average. A very muscular person may show a falsely low eGFR. Someone with low muscle mass — frail, elderly, or after significant weight loss — may show a falsely reassuring one.

This is why eGFR is paired with a urine test. The urine albumin-creatinine ratio (uACR) detects small amounts of protein leaking into the urine, which often appears before filtration measurably drops. Together the two give a far more reliable picture than either alone.

When Cystatin C is used instead

Where the creatinine-based estimate is likely to be unreliable — unusual muscle mass, significant weight change, or a borderline result that needs confirming before a decision is made — an alternative marker called Cystatin C can be measured. It is produced at a steadier rate across the body and is far less affected by muscle, which makes it a useful cross-check when the creatinine picture is ambiguous.

Why this matters particularly in Malaysia

Malaysia carries a heavy burden of kidney disease, driven largely by the prevalence of type 2 diabetes and hypertension. Both damage the small vessels in the kidney quietly, over years, without symptoms. By the time swelling, fatigue or changes in urination appear, considerable function has often already been lost.

That is the practical argument for checking eGFR as part of routine screening rather than waiting for a reason. If you live with diabetes, high blood pressure, obesity, or have a family history of kidney disease, annual monitoring is reasonable — and the earlier a downward trend is spotted, the more can be done to slow it.

What to do with a low result

Do not treat one number as a verdict. A sensible sequence is:

1. Repeat the test. A confirmatory result, ideally well hydrated and without a heavy meat meal beforehand, filters out most false alarms.
2. Check the urine. A uACR tells you whether the kidney is leaking protein, which changes the interpretation considerably.
3. Review the drivers. Blood pressure, blood sugar, weight and medications are where most of the modifiable risk sits.
4. Track the trend. A stable eGFR of 70 is a very different situation from one that has fallen from 95 to 70 in two years.

Trend is genuinely the most informative part, and the part most often lost when results are collected from different places and never compared.

At HDC Medical, every screening is dietitian-led — your kidney markers are explained one-to-one alongside the metabolic results that usually drive them, with practical dietary steps attached. Kidney function sits within our full body health screening , together with liver, heart and metabolic markers.

This article is for general education and does not replace personalised medical advice. Reference ranges vary between laboratories — always interpret your results with a qualified professional. Blood screening is a monitoring and early-flag tool, not a diagnosis. HDC Medical is a dietitian-led health screening centre in Oval Damansara, Kuala Lumpur.