Monday, April 8, 2013

Creatine is not just Creatinine misspelled

A few years ago I had a pre-med student shadow me on the dialysis service for a week or two. I had a hard time teaching him because he was so early in his medical education. I had him investigate an issue that he had some personal contact with and I think he did a nice job. The question was, "Is creatine nephrotoxic (bad for the kidneys)."

From this commercial sight, their
information is pretty tight
Creatine is synthesized by the body from the amino acids arginine, glycine, and methionine. It is phosphorylated by ATP to form phosphocreatine which is stored in muscle cells and acts as an instant energy source. When exercise depletes ATP, phosphocreatine rapidly restores ATP from ADP. Skeletal muscles typically have 3 times as much phosphocreatine as ATP. After being used up creatine is excreted as creatinine (and you thought creatinine's purpose was to measure renal function).

The student, DJ_Scary, put together the following presentation on the biology and nephrotoxicity of creatine.

Medicine tends to be pretty puritanical. If it feels good, don't do it. If it it feels bad, do it more. Eat your vegetables. Exercise every day. Don't drink. Don't smoke, Eat less red meat. Don't put so much salt on your food. When it comes to performance enhancing drugs, the knee jerk and conservative response is the same. Avoid protein supplements. Don't use anabolic steroids. Creatine will damage your kidneys. Some of this advice is wise, Joshua Schwimmer showed that anabolic steroids can cause FSGS (anybody ever test Zo or Sean Elliott for steroids?).

Creatine can double, triple or quadruple a patients serum creatinine. The math on how that works is shown in the video.
Note for the equations to be valid the following assumptions and units need to be used:
  • CrCl: ml/min
  • Creatinine: mg per 24 hours
  • Serum creatinine: mg/dL

The point of the video is that creatine will increase your creatinine and not affect your creatinine clearance or GFR which are the important variables. This is a situation where one cannot trust the estimated GFR formulas.

The medical puritan tells patients not to use creatinine because it can damage the kidney. This is not true. There is no data, beyond some pretty sketchy case reports that creatine can damage the kidney. Long term follow up with medical use of creatine shows no harm (randomized, placebo controlled data!). It seem convincingly safe (Oh, you wanted a Cochrane Meta analysis, we got that here). It will always be safer and more conservative for physicians to tell patients not to take a substance. (One year follow-up too short for you, how does 5 years of follow-up taste?) Patients deserve honest, unbiased answers about what different substances and behaviors do to their bodies and if physicians provide them with the same, old, predictable, puritan, advise, they will bypass doctors and we will lose our role in health advice.

To see a range of nephrologist views on creatine, take a look at the replies to this tweet.

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