Explanation

Protein/creatinine ratio: what is measured?

The protein/creatinine ratio is not a separate measurement but a calculation. The laboratory measures total protein and creatinine in the same urine sample and divides protein by creatinine. Because creatinine is excreted at a fairly constant rate, this division makes the result largely independent of how much you have drunk, so a single urine sample gives an estimate of the protein loss over a whole day. Whereas the albumin/creatinine ratio only counts albumin, this ratio counts all proteins together; the result is given in milligrams of protein per millimole of creatinine (mg/mmol) or per gram of creatinine (mg/g).

What can it detect?

Protein loss through the kidneys and how large it is, also when it involves proteins other than albumin
Temporary protein loss due to heavy exercise, fever or a urinary tract infection
In pregnancy: protein in the urine, which counts together with blood pressure in the assessment of preeclampsia

Result

What does the result mean?

Protein/creatinine ratio too high

A raised ratio means that there is more protein in the urine than fits the dilution. This usually points to damage to the kidney filters, for example due to diabetes or high blood pressure, sometimes to a kidney disease, and is often temporary after heavy exercise, with fever, a urinary tract infection or during menstruation. In pregnant women with high blood pressure, according to the Dutch medical specialists' guideline (FMS) on hypertensive disorders in pregnancy, a ratio below 30 mg/mmol counts as not abnormal and above 50 mg/mmol as abnormal (in mg/g roughly 265 and 440); in between, the midwife or gynecologist decides on a repeat test. In people with little muscle mass the ratio is somewhat higher, because they excrete less creatinine. Rarely, proteins end up in the urine because the body makes too much of an abnormal protein; this calls for further testing.

Protein/creatinine ratio too low

A low ratio is favorable and fits kidneys that let almost no protein through; a value that is too low does not exist as a problem. In people with a lot of muscle mass the ratio is somewhat lower, because they excrete more creatinine. A normal ratio does not rule out early kidney damage, because a small amount of albumin gets lost among the other proteins, nor a reduced filtering function; that requires the albumin/creatinine ratio and the eGFR in blood.

After an abnormal result

With a raised ratio, the GP rules out a urinary tract infection, repeats the measurement in morning urine, usually as the albumin/creatinine ratio, and has the eGFR in blood measured. If the protein loss persists, the GP assesses the cause and risk according to the NHG guideline on chronic kidney damage. With a lot of protein, a rapidly declining kidney function or protein together with blood in the urine, referral to an internist-nephrologist may follow.

Reliability

How reliable is the test?

The ratio is a better measure of protein loss than the protein concentration alone, because it corrects for the dilution of the urine. To detect and classify chronic kidney damage, the Dutch GP guideline (NHG) on chronic kidney damage does not use this ratio but the albumin/creatinine ratio, which detects early kidney damage sooner. The protein/creatinine ratio does count proteins that the albumin/creatinine ratio misses, and the FMS guideline on hypertensive disorders in pregnancy uses it in the assessment of preeclampsia. Because protein in the urine varies from day to day, a raised ratio is confirmed with a repeat measurement.

What can affect the result?

Heavy exercise, fever, a urinary tract infection, dehydration and menstruation can raise the ratio temporarily.
Muscle mass affects the excretion of creatinine: with little muscle mass the ratio is higher, with a lot of muscle mass lower.
Morning urine gives the most comparable result; the urine must not be frozen.
Measurement methods for total protein do not react equally strongly to all proteins, so results can differ between laboratories.

Preparation

Preferably use morning urine.
Do not do heavy exercise in the 24 hours before collecting the urine; it temporarily raises protein in the urine.
Do not collect urine during your period.

Who it is for

Who is the test useful for?

Useful for

Useful for following up a positive urine dipstick or protein in the urine and for monitoring known protein loss, for example in kidney disease. For detecting early kidney damage in diabetes, high blood pressure or cardiovascular disease, the albumin/creatinine ratio is more sensitive, together with the eGFR in blood. If you are pregnant and have a headache, see stars or flashes of light, have pain in your upper abdomen or high blood pressure, contact your midwife or gynecologist the same day; this test does not replace that check.

How common is it?

Chronic kidney damage affects about 1 in 10 adults in the Netherlands, more often at older ages and in people with diabetes and high blood pressure. Protein in the urine is often the first sign. In about 5 in 100 Dutch people, chronic kidney damage is known to the GP; so many people with kidney damage do not know it.

NHG guideline on chronic kidney damage; NIVEL primary care registrations (2021)

Drawbacks and risks

A temporarily raised value after exercise or with an infection can, without a repeat measurement, wrongly look like kidney damage and cause unnecessary worry.
A normal ratio can give false reassurance in diabetes or high blood pressure, because early kidney damage is visible sooner with the albumin/creatinine ratio.

Get tested

Protein/creatinine ratio: test panels

Protein/creatinine ratio is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Urine · 3 analyses
Protein/creatinine ratio
Measures total protein and creatinine in urine and calculates the protein/creatinine ratio. To follow up protein in the urine or monitor protein loss.
€ 23,00

Evidence

Sources

This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.

More about risks and results

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