Single marker guide · Kidney function (eGFR, cystatin C, creatinine, ACR)
One in ten UK adults has chronic kidney disease and around a million of them do not know, because kidneys produce no symptoms until most of their function is gone. The standard test, creatinine, has a flaw that makes this worse: it reads wrong in anyone muscular, anyone slim, and anyone over 65. Cystatin C fixes that. Urine ACR catches damage years before either. Here is what each one shows and how to test properly.
Venous draw at 103 UK clinics or at home. UKAS-accredited laboratory. Report reviewed by a medical professional.
The short answer
Your kidneys filter your blood, and the standard way to measure how well is to check a waste product that should be filtered out. Creatinine is that waste product, and eGFR, the number you see on an NHS result, is a calculation of filtering rate based on your creatinine, age and sex. The problem is that creatinine comes from muscle. A lean, muscular 30-year-old who eats meat and takes creatine produces a lot of it, so their eGFR reads low and they are told to worry. A slim 70-year-old with little muscle produces very little, so their eGFR reads high, and genuine kidney decline is missed. The population most at risk of kidney disease is exactly the population creatinine flatters.
Cystatin C is a small protein made by every cell in the body at a steady rate, filtered by the kidneys, and unaffected by muscle mass, diet or supplements. An eGFR calculated from cystatin C is the number NICE now recommends to confirm or rule out early kidney disease when creatinine is borderline. TrueVitals measures both in the Ultimate panel, so a discrepancy between them, which is common, is caught rather than missed. Why gym-goers get false kidney alarms.
Reference ranges
| eGFR (mL/min/1.73m²) | Stage | What it means |
|---|---|---|
| 90 and above | G1 · Normal | Full filtering capacity. Kidney disease can still be present if ACR is raised, which is why the two are read together. |
| 60 to 89 | G2 · Mildly reduced | Normal for most adults over 40 and not a disease on its own. Worth tracking year on year: a steady fall of more than 5 a year matters even inside this band. |
| 45 to 59 | G3a · Mild to moderate | Chronic kidney disease if persistent over three months. This is where cystatin C earns its place: NICE recommends it here to confirm the result is real rather than a muscle artefact. |
| 30 to 44 | G3b · Moderate to severe | Established kidney disease. GP management of blood pressure, blood sugar and medication doses. Cardiovascular risk rises sharply from here. |
| 15 to 29 | G4 · Severe | Specialist referral. Symptoms typically begin at this stage, which is the point of testing before it. |
| Below 15 | G5 · Kidney failure | Dialysis or transplant planning. |
Stages follow the KDIGO classification used by NICE. Urine albumin-to-creatinine ratio (ACR) adds a second axis: below 3 mg/mmol is normal (A1), 3 to 30 is moderately raised (A2), above 30 is severely raised (A3). A normal eGFR with a raised ACR is still kidney disease, and it is the earliest form there is.
Why it matters
Like the cardiovascular markers, kidney function has no symptoms until it is late. Tiredness, swollen ankles, foamy urine, itching and nausea arrive at stage 4, by which point around three quarters of function is gone and the remaining options are about slowing decline rather than reversing it. Caught at stage 2 or 3a, the same decline is often stoppable with blood pressure control, blood sugar control and stopping the medications that were causing it. The whole value of the test is in the years between those two points.
Together they account for most kidney disease in the UK, and both are silent themselves. Anyone with prediabetes, a high HbA1c or a blood pressure above 130/80 should know their kidney numbers. Prediabetes guide.
Regular ibuprofen, naproxen or diclofenac, including gels, reduce blood flow to the kidneys. Years of daily use for a bad back is a recognised route to kidney damage, and the test is the only way to know whether it is happening to you.
Reduced kidney function raises cardiovascular risk more than smoking does. It raises Lp(a), blood pressure and inflammation, and lowers the body's ability to clear the particles that cause plaque. A falling eGFR changes every other target in the report. Heart health guide.
Who should test
Anyone with diabetes or prediabetes, high blood pressure, a family history of kidney disease, or a heart condition, because these are the causes. Anyone taking regular anti-inflammatory painkillers, lithium, some blood pressure drugs, or high-protein supplements. Anyone with recurrent urinary infections or kidney stones. And two groups where the standard test specifically fails: people with high muscle mass, whose creatinine flags a problem that is not there, and people with low muscle mass, older adults, the very slim, and anyone who has lost weight quickly, whose creatinine hides a problem that is. For both, cystatin C is the test that tells the truth. Blood tests for the over 40s.
Read it in context
eGFR tells you how well the kidneys are filtering today. The markers beside it tell you whether the number is trustworthy, what is causing any decline, and how urgent it is.
Two independent estimates of the same thing. When they agree, the result is solid. When they disagree, the cystatin C is usually right, and the gap itself tells you something about muscle mass or a measurement artefact. Both in Ultimate.
Albumin leaking into urine is the first sign of kidney damage, appearing years before eGFR falls. It is the test NICE recommends annually for everyone with diabetes or hypertension. Available as an add-on to any TrueVitals panel; urinalysis in Ultimate gives a dipstick protein reading as a first screen.
Diabetes is the leading cause of kidney failure, and kidney damage starts in the prediabetic range. Reading kidney function next to glucose control tells you whether blood sugar is the driver. Insulin and HOMA-IR are in Ultimate.
The electrolytes the kidneys regulate. Rising potassium or urea with a falling eGFR shows the decline is affecting function, not just the number. In every panel.
Raised uric acid both damages the kidneys and results from reduced clearance, and it is the marker behind gout. High uric acid with a borderline eGFR is a pattern worth acting on early. Joint pain blood test guide.
Kidneys make the hormone that drives red cell production and control calcium and phosphate balance. Anaemia, high phosphate or raised parathyroid hormone alongside a low eGFR show the disease has been established long enough to affect other systems. PTH is in Ultimate.
Which test
Advanced
74 biomarkers · £269
Creatinine, eGFR, urea, sodium, potassium, chloride, bicarbonate and uric acid, with HbA1c, full blood count, liver, lipids and ApoB. The standard kidney profile inside a full baseline.
View AdvancedIncludes cystatin C
Ultimate
114 biomarkers · £349
Everything in Advanced plus cystatin C with its own eGFR, urinalysis, calcium, phosphate, parathyroid hormone, fasting insulin and HOMA-IR. The muscle-independent kidney picture, with the metabolic causes beside it.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. Extended renal, metabolic syndrome and cardiovascular screening on top of everything above, with physical measurements including blood pressure.
View SignatureUrine ACR available as an add-on to any panel. Clinic draw £19 at 103 UK clinics. At-home phlebotomist £39 across 200+ areas. Fast from 10pm the night before.
Honest comparison
If you have diagnosed diabetes, hypertension or kidney disease, your GP should be testing eGFR and ACR every year already, and that is free and appropriate. If you are on a medication that needs kidney monitoring, the NHS does that too. A standalone kidney profile from Medichecks costs around £39 and is fine for a quick recheck of a known creatinine.
A panel is the better choice when nobody has looked, when you fall into a group creatinine misreads, or when you want the causes tested alongside the effect: blood sugar, blood pressure markers, uric acid, inflammation and the cardiovascular picture that a falling eGFR changes. Cystatin C in particular is rarely offered outside a panel, and it is the test that settles whether a borderline result is real. See how every UK provider compares.
After the result
Kidney function is fine. Note the number and retest annually so you can see the trend; a slow decline inside the normal range is the earliest possible warning and only visible over time.
Trust cystatin C. If creatinine eGFR is low but cystatin C eGFR is normal, muscle mass is the explanation and there is nothing to treat. If it is the other way round, the creatinine has been hiding a decline and the cystatin C result is the one to take to your GP.
Take your report to your GP for a repeat in three months, which is what defines chronic kidney disease. Meanwhile the levers are blood pressure below 130/80, blood sugar control, stopping regular anti-inflammatory painkillers, staying hydrated and not smoking. Most early kidney disease is stabilised by exactly these.
This page is general information, not medical advice. A sudden fall in urine output, severe swelling or breathlessness needs urgent medical attention.
FAQs
Creatinine and urea, waste products the kidneys should clear, plus the electrolytes they regulate. From creatinine, age and sex, the laboratory estimates your filtering rate as eGFR. Cystatin C provides a second, muscle-independent estimate, and urine ACR detects albumin leaking through damaged filters.
90 and above is normal; 60 to 89 is mildly reduced and usually fine, especially over 40; below 60 sustained for three months is chronic kidney disease. Because eGFR is reported as "above 60" on many NHS results, a decline from 95 to 65 over a few years can go entirely unremarked.
Creatinine comes from muscle, so eGFR from creatinine reads too low in muscular people and too high in slim or older people. Cystatin C is produced by all cells at a constant rate and is unaffected by muscle mass, diet or creatine supplements. NICE recommends it to confirm early kidney disease when creatinine eGFR is 45 to 59 with no other signs.
Yes. High muscle mass, a high-protein diet, creatine supplements and hard training in the days before a draw all raise creatinine and lower the calculated eGFR without any kidney problem. Cystatin C is unaffected, which is why it is the right test for anyone who trains seriously.
Albumin-to-creatinine ratio, measured in a urine sample, detects protein leaking through damaged kidney filters. It is the earliest sign of kidney disease, often appearing years before eGFR falls, and NICE recommends it annually for anyone with diabetes or high blood pressure. It is available as an add-on to any TrueVitals panel.
Not for kidney markers, though a large meat meal the night before raises creatinine slightly. TrueVitals panels also include glucose, insulin and triglycerides, so we ask you to fast from 10pm the night before and drink water as normal. Being well hydrated matters: dehydration raises creatinine and urea on its own.
Yes, creatinine and eGFR are part of a standard renal profile and are tested regularly in people with diabetes, hypertension or known kidney disease. Cystatin C is rarely used outside specialist settings, and ACR is often missed in people who have not been diagnosed with a risk condition. What to ask your GP for.
A standalone kidney profile is around £39. A TrueVitals Advanced panel is £269 and includes the full renal profile with HbA1c, lipids, ApoB and 60 other markers; Ultimate at £349 adds cystatin C, urinalysis, PTH, calcium, phosphate and fasting insulin. Urine ACR can be added to either.
74 to 230 biomarkers. Venous draw at 103 UK clinics or at home. A report that tells you what your results mean and what to do next.
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