Creatine and kidney values: how to interpret a rise in creatinine

An unusual creatinine value after starting creatine needs context. On its own, it proves neither kidney damage nor that everything is harmless. The common explanation “that’s just the creatine” can be just as hasty as automatically equating the value with a kidney problem.

What counts for interpretation is the trend over time, the other findings and your personal history. Creatine use is therefore part of the information you should mention when blood is drawn and in the conversation that follows.

What a controlled study found

One study recruited 36 healthy male students and compared placebo with 3 or 5 grams of creatine a day over 35 days. There were no significant differences between the groups in the kidney parameters examined, including additional markers such as KIM-1 and MCP-1. Within the creatine groups, creatinine rose and the filtration rate estimated from it fell; the values stayed within the reference range. Vilar Neto et al., 2020

For the situation studied, that is a reassuring finding, but it does not amount to a blanket safety guarantee. A short trial in healthy young men does not answer a long-term question for someone with existing kidney disease. Nor does it rule out every rare adverse effect.

Keep measurement, estimate and diagnosis apart

Creatinine is produced, among other ways, through creatine metabolism. A change in this marker can therefore affect how a creatinine-based eGFR is interpreted. The eGFR is a calculated estimate, not a direct measurement of filtering capacity. This distinction explains why a single value should not be looked at in isolation. Vilar Neto et al., 2020

For further assessment, it needs to be clarified which information about the trend is still missing. Whether further tests are needed depends on that and on the overall situation. An additional marker, too, can only be interpreted in this context and offers no infallible all-clear.

How to make the conversation with your doctor more concrete

The package, or a photo of the ingredient list, makes the conversation easier. It also helps to say when you started taking it, how much you intend to take and whether it is a pure creatine product or a blend. Other medications and supplements are relevant as well. Earlier lab results can help in judging the trend.

Any change in intake before a planned test should be discussed with the practice. That includes a pause meant to influence the lab value. The care team needs to know under what conditions the follow-up value was obtained in order to compare it meaningfully.

Why existing kidney disease is considered separately

The statement “no harm found in healthy participants” cannot simply be applied to a person with reduced kidney function. Anyone already being treated for kidney disease, or with unexplained abnormal values, should discuss taking creatine with their treating practice beforehand. A general product description cannot replace that decision.

Nor does the study described here call for a comprehensive lab panel for every healthy adult. It shows how carefully kidney values were interpreted in a research setting. Whether any monitoring is needed in everyday life, and which kind, remains an individual question.

So mention creatine use when you have lab tests. Abnormal findings need to be interpreted together with your care team; reassuring study results apply first of all to the people and conditions that were actually studied.