Kidney Function
Table of contents
My April screening had my kidney numbers sitting on the low side of normal: creatinine at 108 and an estimated filtration rate of 77. They weren’t flagged, but they weren’t what you’d expect from a healthy 34-year-old either. By October both had bounced back to clearly normal. This article covers what these markers are, why April probably looked worse than reality, and the one urine question that’s still open.
Snapshot
| Marker | April 2026 | October 2026 | Normal range | Status |
|---|---|---|---|---|
| Creatinine | 108 µmol/L | 88 µmol/L | 50–120 | ✅ |
| eGFR | 77 | 102 mL/min/1.73m² | >90 is normal | ✅ |
| Urea | 7.45 mmol/L | 8.04 mmol/L | 2.76–8.07 | ⚠️ top of range |
| Urine protein (dipstick) | Trace (+) | Not retested | Negative | ⚠️ still open |
| Urine microalbumin | <4 mg/L | <4 mg/L | Below detection is good | ✅ |
Here’s the section of my October lab report, which shows both dates side by side:
What these markers are
- Creatinine is a waste product from muscle. Your muscles break down a little creatine every day, it ends up in the blood as creatinine, and healthy kidneys filter it out. If the kidneys filter less, creatinine builds up.
- eGFR (estimated glomerular filtration rate) isn’t measured directly. The lab calculates it from creatinine, age and sex. It’s an estimate of how much blood your kidneys filter per minute. Above 90 is normal; 60–89 is “mildly reduced” if it stays that way.
- Urea is the waste product from breaking down protein. It goes up with a high-protein diet and with dehydration.
- Urine protein (dipstick) is a quick strip test. Healthy kidneys keep protein in the blood, so any protein in urine is worth a second look.
- Urine microalbumin is a more sensitive test for small amounts of albumin (the main blood protein) leaking into urine. It’s one of the earliest signs of kidney stress.
The catch with creatinine is that it depends on how much muscle you have and how hydrated you are, not just on your kidneys. A muscular person can have a higher creatinine with perfectly healthy kidneys, and being a bit dry on test day concentrates everything in the blood.
What I’m aiming for
For me, the aim is simple: eGFR above 90 and no protein in my urine. I don’t need a particular creatinine number, because mine moves with my muscle mass and training. As a lean BJJ athlete on a high-protein diet, I’d expect creatinine and urea to sit in the upper half of normal. That’s fine as long as eGFR stays above 90.
Why April looked like a problem
On paper, April’s eGFR of 77 is “mildly reduced”. If that had stayed there, it could point to the kidneys filtering less than they should. Over years, reduced kidney function raises blood pressure and heart risk, and it’s mostly silent until it’s advanced. That’s why a low eGFR at 34 is worth taking seriously, even when it isn’t flagged.
On top of that, the April urine dipstick showed trace protein. On its own, that could mean the kidneys are letting protein through.
But there were good reasons to think April was a hydration and training effect rather than real kidney damage:
- My urine was concentrated. The urine creatinine in April was 17.30 mmol/L, which is high and usually means not drinking enough before the test.
- Microalbumin was below detection (<4). That’s the more sensitive test, and it was clean. A trace on the dipstick with clean microalbumin often turns out to be temporary.
- Hard training causes temporary urine protein. Exercise-related proteinuria is common and usually clears within a day or two of rest.
- Other “edge of range” numbers in April (urea 7.45, uric acid 0.46) also fit being a bit dry.
Why October is better, and what probably helped
October’s creatinine 88 and eGFR 102 are clearly normal. What makes this convincing is that I gained about 1.4 kg of lean mass between April and October (see Lean Mass). More muscle should push creatinine up, but it went down. That points strongly to April being a hydration effect rather than a real kidney issue.
What probably helped:
- Better hydration on test day. My October urine was very dilute (urine creatinine 3.02), the opposite of April. I was drinking properly, partly because I’d been warned off dehydrating during the competition cut while on anti-inflammatories.
- No hard training right before the draw. The October test was nine days after my BJJ competition, and I was out of training with an elbow injury.
Urea is at the top of its range (8.04). That’s typical of a high-protein diet, and I did increase my protein after April. With creatinine and eGFR both normal, it’s not a kidney warning. If it ever went above the range alongside a falling eGFR, it would be.
What’s still open
- The trace urine protein from April hasn’t been retested. October’s package didn’t include a urine dipstick. And while microalbumin was again below detection, my urine was so dilute that the result says very little. I want a repeat urinalysis on a rest day, normally hydrated, ideally with a urine albumin-to-creatinine ratio.
- Watch NSAIDs. I took a course of etoricoxib (Arcoxia) in October for a neck injury, and NSAIDs plus dehydration are hard on the kidneys. My eGFR was fine afterwards, but I don’t want to rely on anti-inflammatories long term. More on that course in ALT, Etoricoxib & My Neck.
This is my own personal data, shared for interest only. It’s not medical advice.
Until next time, peace and love!