A High Creatinine with a Normal eGFR
Creatinine is a waste product of muscle, so how much of it you produce depends on how much muscle you carry. A weightlifter and a frail eighty-year-old with identical kidneys will not have identical creatinines. When the eGFR beside it comes back normal, the equation has already made that adjustment and concluded your filtration is fine.
The pattern on your report
- Creatinine High · mild Key
- eGFR Normal Key
- Urea Normal Key
- Potassium Normal Supporting
Printed as: Urea in mmol/Lor mg/dL— Two different measurements as well as two notations: the SI form reports urea, the US form reports the nitrogen in it, which is why the figures look unrelated.Creatinine in umol/Lor mg/dL— Far apart: 88 umol/L is about 1.0 mg/dL. Check which notation your report uses before comparing it with a range from another country.eGFR in mL/min/1.73m2— One notation, though the equation behind it has changed over the years and differs between countries, so an older result may not be directly comparable.Potassium in mmol/Lor mEq/L
Why the numbers look like this
Muscle breaks down creatine phosphate at a steady daily rate, producing creatinine, which the kidney filters out. Because production is steady, the blood level is a usable proxy for filtration. Because production is proportional to muscle mass, the same filtration produces a different blood level in different bodies.
The eGFR equations exist to correct for that, using age and sex as stand-ins for muscle mass. They work well across most of the population and poorly at the extremes, which is exactly where this pattern arises: someone whose muscle mass is far from what their age and sex predict. NICE says so directly, advising that eGFR be interpreted with caution in adults with extremes of muscle mass, naming bodybuilders and people who have had an amputation.
Creatinine also rises without the kidney being involved at all. A large meat meal in the hours before the draw does it, so do creatine supplements, and so do several common medicines that block creatinine's secretion into the urine while leaving filtration untouched.
Not being flagged is not the same as normal
Printed creatinine ranges are typically somewhere around 60 to 110 umol/L for men and lower for women, and they vary between laboratories and by the assay method. That variation is why the eGFR, not the creatinine, is the number to read: it is calculated from the same result but adjusted for the things that make a raw creatinine hard to compare between people.
One piece of preparation before your next test: NICE advises not eating any meat in the 12 hours before a creatinine-based eGFR sample, because a meat meal raises the result for hours afterwards.
What else on the report can hide this
Urea is the companion number that separates the explanations. Dehydration raises urea proportionally more than creatinine; muscle mass raises creatinine while leaving urea alone. So a high creatinine with a completely ordinary urea points away from anything to do with fluid or filtration.
Cystatin C settles it where it matters. It is filtered like creatinine but produced by nearly all cells, not by muscle, so how much of you is muscle stops mattering. An eGFR calculated from cystatin C is the test for athletes, bodybuilders, amputees and anyone whose creatinine has never fitted their kidneys.
The urine matters too. Kidney damage is staged by filtration and by protein leak together, and a normal eGFR with protein in the urine is a real finding that this pattern can hide behind.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
High muscle mass
Weight training, a large frame, or simply being muscular. NICE names this explicitly as a reason to interpret eGFR with caution, and cystatin C is the way around it.
- Very common
A meat meal before the test
Cooked meat contains creatinine directly and raises the blood level for hours. NICE advises avoiding meat for 12 hours before the sample.
- Common
Creatine supplements
Widely used in strength training. It raises measured creatinine without harming the kidney, and the effect disappears within weeks of stopping.
- Common
Medicines that block creatinine secretion
Trimethoprim, cimetidine, cobicistat, dolutegravir and fenofibrate stop the kidney secreting creatinine into the urine while filtration continues unchanged. The rise appears within days of starting and reverses on stopping.
- Common
Laboratory and assay variation
Different methods give different creatinine values for the same blood, which is why a result should be compared with previous ones from the same laboratory where possible.
- Uncommon
Early kidney disease that the equation is missing
The equations are least accurate near the top of their range. A urine ACR and a repeat over months are what catch this, not a single eGFR.
- Uncommon
A recent very heavy workout
Muscle breakdown after unaccustomed exercise raises creatinine along with CK. It settles within days, and a markedly raised CK is a different situation entirely.
What is usually checked next
- Cystatin C, with an eGFR calculated from it Measures filtration without depending on muscle mass. The definitive test for this pattern, and one to ask for by name.
- Urine albumin-to-creatinine ratio Kidney damage is staged by protein leak as well as filtration, and this catches the damage a normal eGFR does not show.
- Repeat after 12 hours without meat and without creatine Removes the two dietary causes at once, and needs no new kind of test.
- A medication review Identifies the drugs that raise creatinine by blocking its secretion rather than by harming the kidney.
- Your previous creatinine results A value that has been steady for years alongside a stable eGFR describes your normal, not a change.
When to seek care sooner
- Emergency Passing very little urine, or none
- Emergency Dark or cola-colored urine after intense exercise, with muscle pain
- Same day Swelling of the legs or face with breathlessness
- Same day A creatinine that has risen substantially since the last test
- Soon Protein or blood found in the urine
Questions worth bringing to your appointment
- Given how much muscle I carry, would a cystatin C give a truer picture?
- Had I eaten meat or taken creatine before this test?
- Could trimethoprim or another medicine be raising it without affecting my kidneys?
- Has my urine been checked for protein?
- How does this compare with my creatinine from previous years?