Does high creatinine mean kidney failure?

“My creatinine is high. Does that mean my kidneys are ruined?” Most patients ask this the moment they see the lab sheet. The short answer: a high creatinine should be taken seriously and followed up, but on its own it is not a diagnosis of kidney failure.

What is creatinine?

NKF describes creatinine as a waste product from the normal breakdown of muscle, which the kidneys remove from the blood. Everyone has some creatinine. When the kidneys work less well, creatinine builds up in the blood and the number goes up. That is why doctors use it to follow the kidneys.

Why is one number not enough?

The “normal” number is not the same for everyone. NKF writes that the normal limit varies with age, sex, body size and other factors, so always look at the reference range on the sheet from the same lab.

Things that raise creatinine without the kidney being damaged (NKF):

• Eating a lot of cooked meat. You may be asked not to eat meat the night before a test.
• Creatine supplements.
• Recent hard exercise.
• Large muscle mass.
• Some medicines, including cimetidine, trimethoprim, fenofibrate, ritonavir and dolutegravir. If you take one of these, do not stop it yourself and tell your doctor.

Things that lower it: a plant-based diet, low muscle mass, pregnancy, amputation or muscle diseases, and severe liver disease (NKF). That means creatinine can be “normal” and a kidney problem can still be present. NKF says plainly that a “normal” result can go with kidney disease, and a “high” result does not always mean kidney disease or serious illness.

From creatinine to eGFR

The doctor converts creatinine, with age and sex, into an eGFR, which NKF considers a better measure of kidney function. Sometimes another test called cystatin C is used too, and NKF says an eGFR built from both is more accurate. If eGFR is low, NKF suggests these questions:

• Do I need a urine (albumin) test as well?
• Could dehydration, illness or an infection have changed the number for a while?
• Do my medicines need review?
• Should I see a nephrologist?

For the table of stages and what the numbers mean, see the guide “Kidney tests”.

When is it called kidney disease?

NKF says chronic kidney disease means damage or reduced function that lasts three months or more. For a low eGFR, NKF also suggests repeating it after about three months. So one bad test, even if upsetting, is still not a diagnosis. That does not mean waiting: show the result to your doctor soon, and if the number has jumped compared with before, make contact the same day. The doctor considers looking at the trend more useful than a single number.

If the number stays bad after several tests, the doctor looks for the cause: blood pressure, diabetes, protein in the urine, stones or a blocked urinary tract, medicines and diseases of the kidney’s filters (NHS).

If your creatinine has come back high, what should you do?

• Do not panic, but do not leave it either. Show the result to your doctor. NHS says chronic kidney disease is diagnosed with blood and urine tests, and NIDDK counts the two tests, eGFR and urine albumin, as the yardstick.
• Find your earlier results. The trend over time says much more than one number.
• Write a full list of medicines and supplements. Even sports and herbal supplements.
• Do nothing on your own before the second test. Do not go on a strict diet, take a “kidney cleanse” supplement or stop your medicine.
• Do not take anti-inflammatory painkillers unless your doctor says so (see the guide “Medicines, painkillers, herbs and contrast dye”).
• If you are passing very little urine, or have sudden swelling or shortness of breath, or severe vomiting and diarrhoea, do not wait for an appointment and see the guide “When to get urgent help”.

In summary

A high creatinine means a closer look is needed. On its own it is not a diagnosis of kidney failure, and no decision about dialysis is made from one number. The answer comes from repeated tests, eGFR, a urine test and the doctor’s assessment. Interpreting your own number is for your doctor only.