Can a Creatine Supplement Raise Creatinine and Lower eGFR?

Yes, it can. The National Kidney Foundation lists taking creatine supplements as one of the factors that can raise blood creatinine. Because the standard eGFR is calculated from creatinine, a higher level can make the eGFR look lower than the kidneys' actual filtering ability.

That does not mean every raised creatinine in someone taking creatine is caused by the supplement. The same blood result can also reflect reduced kidney function, dehydration or other problems, so the result still needs to be reviewed in context. This guide explains the link and the questions to ask; it cannot tell you what your own result means.

A test result on its own is not usually an emergency, but some symptoms can point to acute kidney injury (AKI), a sudden drop in kidney function. The NHS lists the symptoms below and advises getting an urgent appointment or help from a service such as NHS 111 if you think you may have AKI. Outside the UK, use your local urgent care or emergency number.

Many people with mild AKI have no symptoms, which is why an abnormal result should not simply be left until a routine review if the requesting team has asked you to act sooner.

• Peeing a lot less than usual.
• Feeling very thirsty, or having nausea or vomiting.
• Swollen feet or legs.
• Tiredness, dizziness, confusion or sleepiness.
• Breathlessness, especially when lying down.

The names are similar, but they are not the same substance. Creatinine is a waste product that comes from the normal use of muscle. The kidneys filter it out of the blood, so blood creatinine is used as a marker of how well they are filtering.

MedlinePlus explains that people make different amounts of creatinine depending on how much muscle they have, and that a person's usual range depends on muscle mass, diet, age and activity. That is why a creatinine result is always read against the person, not just against a printed range. Laboratory ranges also differ, so use the range on your own report.

eGFR stands for estimated glomerular filtration rate. The National Kidney Foundation explains that the standard eGFR is calculated from blood creatinine together with age and sex. It is an estimate, not a direct measurement of filtration.

If something raises creatinine without changing kidney filtration, the calculation reads that higher creatinine as weaker filtering. The National Kidney Foundation lists several such factors:

• Taking creatine supplements.
• High muscle mass, for example a very muscular build.
• Eating a large amount of cooked meat before the test.
• Recent high-intensity exercise.

There is no reliable number to apply to an individual result. The National Kidney Foundation says the effect of these factors is highly variable and that people respond very differently to them. It also notes that in some less common situations, people may be asked not to eat cooked meat the night before a test.

Because the effect cannot be predicted, the safest approach is not to explain the result away yourself. A clinician may compare it with earlier results, look at urine tests, check your symptoms and consider a repeat test. The National Kidney Foundation's suggested questions include asking whether an eGFR test should be repeated in about three months to see whether a lower value persists. If you have had a single low reading, our guide on one low eGFR result covers that step in more detail.

It may help. Cystatin C is a protein the body makes, and the National Kidney Foundation says it can be used to calculate eGFR instead of, or alongside, creatinine. It describes cystatin C as possibly more accurate for people with high muscle mass, whose creatinine levels can vary, and for situations where an earlier kidney test did not give a clear answer.

The National Kidney Foundation also states that an eGFR calculated from both creatinine and cystatin C is more accurate than either value alone. Cystatin C has its own limits: the same organisation notes it may not be accurate in people with untreated thyroid conditions or people taking steroids. Whether it is available or needed is a decision for the clinician and the laboratory.

Tell the person reviewing the result that you take creatine, and mention every other supplement, prescribed medicine and over-the-counter product. MedlinePlus notes that certain medicines and supplements can affect test results. Also mention recent intense training, a high-protein or meat-heavy diet and anything that may have left you dehydrated.

Do not stop or change a prescribed medicine to improve a kidney result without talking to the prescriber first. Some medicines are risky to stop suddenly; the NHS, for example, warns that stopping some steroid medicines suddenly can cause symptoms and advises talking to a doctor first. Ask the clinician how to handle supplements before any repeat test rather than guessing, and the NHS also advises speaking to a doctor before starting new medicines or supplements if you are at risk of kidney injury.

Take the full report, including the units and the laboratory's reference range, and earlier results if you have them.

• Could creatine, my muscle mass, exercise or diet explain part of this result, and what other causes are you still considering?
• Do my urine tests, symptoms or previous results change how you read this eGFR?
• Should the test be repeated, and is there anything I should do differently before the repeat?
• Would an eGFR using cystatin C, or both creatinine and cystatin C, be useful in my case?
• Which symptoms should make me seek help before the next planned test?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a raised creatinine while taking supplements described their results and follow-up can help you notice details worth mentioning and shape your own questions. Other people's cases cannot tell you what your result means or replace a review by your own clinician.