You can test your kidneys with a blood draw and, if it needs to be thorough, a urine sample alongside. The minimum useful panel is creatinine plus the eGFR calculated from it. If you carry a lot of muscle that minimum is too narrow, because creatinine comes from your muscles and distorts your result.
This piece is the practical side. Which values, in which order, and how to keep your measurement clean.
Which blood values do you measure for your kidneys?
Creatinine and eGFR form the base. Urea adds information about protein processing and fluid balance. Cystatin C is the check that does not move with your muscle mass. The urine albumin to creatinine ratio shows first whether your kidney filter is leaking, often years before your eGFR drops.
The order in this table is the order I would add them in.
| Level | What you measure | Who for | What it gives you |
|---|---|---|---|
| Minimum | Creatinine plus eGFR | Anyone wanting a baseline | A first impression, with the muscle mass caveat |
| Athlete base | Add cystatin C | Strength athletes, anyone using creatine | An eGFR that ignores your build |
| Complete | Add urea and urine albumin to creatinine ratio | High blood pressure, diabetes, family kidney disease | The earliest signal of a leaking filter |
| On indication | Uric acid and potassium | Stone formers, users of certain compounds | Context for stones and electrolyte shifts |
That second row is the right starting point for most readers of this site. Why, is explained in cystatin C in muscular athletes.
How do you prepare for a kidney values test?
Draw fasted where you can, well hydrated, and at least 48 hours after your hardest session. Those three things remove most of the noise from your result. Dehydration concentrates your blood and lifts nearly everything, and hard training raises creatinine temporarily.
Say you draw at 8 on Monday morning after a heavy 12 set leg session on Sunday evening. You are mostly measuring your Sunday.
Mention your creatine use too. A reviewer reads a result differently knowing that, which is exactly the point of is creatine bad for your kidneys.
Can you get your kidneys tested without a GP?
Yes. You can order a blood test without a referral and go to a draw point yourself. For athletes that is often the practical route, because a GP rarely orders a kidney panel for someone with no complaints and no risk factors.
That is not a criticism of GPs. Untargeted testing in symptom-free people produces confusion more often than gain, and they have a point.
The difference for our audience is that you do have something to interpret: a build that throws the standard formula off. Our 360 Health test includes creatinine, urea, eGFR and cystatin C in one draw.
How arranging it works in practice sits in testing blood values without a GP.
How often should you test your kidneys?
That depends on your baseline and your risk factors, and it is a question for your GP rather than for a blog. What I can say: a single measurement gives you a starting point, and a second one later gives you a direction.
Without a second point you have no line. With a line you have something you can steer by.
If you measure again, keep the conditions identical. Same time of day, same distance from your last hard session, always well hydrated.
What do you do with the result?
Read it in the context of your build and your week. An eGFR of 72 in a muscular man who uses creatine and trained hard yesterday is a different thing from the same number in a non-training man of 60. The Nierstichting itself notes that muscle mass influences the creatinine value.
If a value stays off across two measurements, see your GP, even if you feel well. Feeling nothing tells you little with kidneys, as kidney damage symptoms explains.
The full explanation of each value and what distorts it in athletes sits in kidney values in athletes.
My advice for a first test: run the panel with cystatin C included. Then you never have to wonder whether the number was about your kidneys or about your back muscles.
References
- Nierstichting. Blood testing for creatinine and kidney function. Accessed 2026.
- Difference between kidney function by cystatin C versus creatinine and association with muscle mass and frailty. J Am Geriatr Soc. 2024. PMID 38819605.
- de Souza e Silva A, et al. Is It Time for a Requiem for Creatine Supplementation-Induced Kidney Failure? A Narrative Review. Nutrients. 2023. PMID 36986197.
Disclaimer
Every blood test result includes a professional assessment from a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. Discuss any abnormal value with your GP.
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