Kidney function (eGFR) and age: why your kidneys slow down

"My kidneys are only working at 70 percent, that's what the lab report said." We hear that sentence often, and there is almost always more fear behind it than is warranted. A gradually lower kidney function is, in fact, frequently part of ageing. The eGFR is an estimate of how well your kidneys clean the blood, and in most people that value declines slowly over the years.

My position: a lower eGFR that fits your age is something quite different from a falling eGFR that warrants concern. The difference lies in the trend, not in a single number.

What is eGFR?

eGFR stands for the estimated rate at which your kidneys filter the blood, expressed in millilitres per minute. The value is calculated from your blood creatinine together with your age and sex. So it is an estimate, not an exact measurement. A higher eGFR usually means a better filtering function. The reference values and the interpretation are on your lab report.

Does kidney function decline with age?

Yes. In most people, eGFR declines gradually from about the age of 30. In healthy people over 70, the value is therefore often lower than in younger people, without any kidney disease being present. The Nierstichting (Dutch Kidney Foundation) stresses that a mildly reduced kidney function at an older age occurs regularly and is not always a problem in itself.

These figures are an aid, not a diagnosis. A doctor looks at the trend and at your other values, such as protein in the urine.

When does an eGFR warrant attention?

A doctor does not look at one measurement, but at the trend over time and at your other values. A one-off slightly lower eGFR can also be linked to drinking too little or a temporary cause, such as an infection. That is why repeating is often worthwhile before drawing conclusions. The NHG guideline used by GPs likewise advises repeating an abnormal value and assessing the picture in context.

Why does your kidney function matter for medication?

Many medicines are removed from the body via the kidneys, and with a lower kidney function they can accumulate. This is particularly a point of attention for older adults taking several medicines, because the correct dose sometimes depends on your eGFR. It is wise to know your kidney function before starting new medication and to discuss this with your GP or pharmacist. Read more about medication and your kidneys and about what changes in your blood values after 60.

Does a reduced kidney function cause symptoms?

In the early stage, you usually do not notice a mildly reduced kidney function. That is exactly what makes a blood test valuable: the kidneys often work less well unnoticed for a long time. Only with a more strongly reduced function can symptoms arise, and these are often not very specific. The Nierstichting (Dutch Kidney Foundation) mentions, among others:

• fatigue and a reduced appetite;
• swollen ankles or a bloated feeling;
• itching or pale skin;
• passing urine more or, conversely, less often than usual.

These symptoms can have many causes and by no means always point to a kidney problem. If you recognise them, discuss them with your GP.

What can temporarily influence the eGFR?

Because the eGFR is calculated from your creatinine, the value can fluctuate due to things that affect creatinine. Eating a lot of meat shortly before the draw, intense exercise, dehydration or certain medicines can temporarily shift the result. A one-off deviation is therefore often a reason to repeat rather than to be alarmed. The NHG likewise advises GPs to confirm an abnormal value before drawing conclusions.

What keeps your kidneys healthy?

You can do a lot yourself to spare your kidneys, mainly by keeping your blood pressure and blood sugar well controlled. The Hartstichting and the Nierstichting point to the same lifestyle factors that also help the heart: not smoking, exercising enough, a healthy weight, and being moderate with salt and alcohol. Drink enough, but do not overdo it: drinking extra water does not make the kidneys work faster. If you regularly use painkillers such as ibuprofen, discuss this with your GP or pharmacist, because long-term use can put a strain on the kidneys.

How often should you check your kidney function?

With a stable, normal value and no risk factors, periodic measuring often suffices. If you have diabetes, high blood pressure or use medicines that pass through the kidneys, more regular checks are usually wise. You determine the right frequency together with your GP; this table only gives a rough guide.

How do you get your kidney function checked?

You can have your kidney function measured with the Levenswijs Diabetes Panel, without a referral. The test measures your creatinine and calculates the eGFR. Because the kidneys play a role in blood sugar regulation and blood pressure, this panel gives a broad picture of your metabolic health.

My advice: know your baseline and track it over time. Always discuss an abnormal result with your GP, if helpful using the explanations on Thuisarts.nl.

Would you like to have your kidney function checked at a calm moment, without first making an appointment with your GP? At Levenswijs Health you can. The result is reviewed by a BIG-registered doctor. A blood test does not provide a diagnosis. For treatment decisions, always discuss your results with your GP.