Key takeaways
- eGFR, estimated glomerular filtration rate, is not measured directly. It is calculated from your creatinine result together with your age and sex, as an estimate of how well your kidneys are filtering.
- Creatinine is a muscle waste product cleared by the kidneys, so muscle mass, a recent meaty meal and hydration can all move the number without kidney function having changed.
- Blood London's Urea and Electrolytes (U&E) profile, which includes creatinine, costs £73.75 plus the £50 blood draw, with results back in 1 day, and no GP referral is needed.
- One low eGFR result is not a diagnosis. Chronic kidney disease is defined on repeated results that stay low over at least three months, not a single blood test.
- Your laboratory report shows the reference range next to each result, and a urine test for protein, called ACR, is often part of a fuller kidney assessment alongside the blood test.
eGFR is an estimate of how well your kidneys are filtering waste from your blood, calculated from your creatinine level together with your age and sex rather than measured directly. The Urea and Electrolytes (U&E) profile at Blood London measures creatinine alongside urea and the main blood salts, with no GP referral needed.
Book a Urea and Electrolytes (U&E) test at 117a Harley Street: £73.75 plus the £50 blood draw, results in 1 day.
What does eGFR actually measure?
eGFR is a calculation, not a direct measurement. Laboratories use your creatinine result, combined with your age and sex, in a standard formula to estimate how much blood your kidneys filter each minute. This estimate is a practical stand-in for a more complex, invasive measurement, and it is the figure doctors use most often to judge overall kidney function. A lower eGFR generally means the kidneys are filtering less effectively, though several everyday factors can shift the number without reflecting a real change in kidney health.
What is creatinine, and why does it matter alongside eGFR?
Creatinine is a waste product made by muscle activity and cleared from the blood by the kidneys, so its level reflects both how much muscle you have and how well your kidneys are filtering it out. Because creatinine comes from muscle, someone with more muscle mass tends to have a naturally higher creatinine, and eGFR calculations adjust for this using age and sex, though not for muscle mass itself. A recent meaty meal, intense exercise or dehydration can all temporarily raise creatinine and lower the calculated eGFR, which is one reason a single result is treated with caution. If you only want this marker, creatinine, including eGFR, can be booked on its own for £39.38 plus the £50 blood draw, with results in 1 day.
What can affect my eGFR result without my kidneys actually changing?
Muscle mass, a recent high-protein or meaty meal, intense exercise beforehand, and hydration status can all move your creatinine and, with it, your calculated eGFR, without your underlying kidney function having changed. This is why a one-off low eGFR is usually followed by a repeat test rather than treated as a diagnosis, and why NICE advises not eating meat in the 12 hours before an eGFR test. Certain medicines can also affect creatinine, so mention anything you are taking when you have the blood drawn.
| Factor | Effect on creatinine and calculated eGFR |
|---|---|
| Higher muscle mass | Creatinine tends to run higher, eGFR calculation adjusts for age and sex but not muscle mass |
| Recent meaty or high-protein meal | Can temporarily raise creatinine |
| Intense exercise beforehand | Can temporarily raise creatinine |
| Dehydration | Can raise creatinine and lower calculated eGFR |
| Genuine reduction in kidney filtering | Raises creatinine and lowers calculated eGFR |
Does one low eGFR result mean I have kidney disease?
No, a single low eGFR result does not mean you have chronic kidney disease. Chronic kidney disease is defined by results that stay reduced when the test is repeated over a period of at least three months, not by one blood test taken on one day. If your eGFR comes back low, the usual next step is a repeat test after a short interval, alongside a review of your hydration, recent diet and any medicines, before drawing further conclusions. Diabetes and high blood pressure are the most common causes of reduced kidney function over time, so blood sugar is often checked alongside kidney markers; our guide explains what your HbA1c result means.
What is urate, and how does it relate to kidney function?
Urate, also called uric acid, is another waste product cleared by the kidneys, and it is sometimes checked alongside creatinine as part of a wider assessment. A raised urate can be linked to gout, and kidney function can influence how well urate is cleared from the blood. Urate (uric acid) can be booked as a standalone test at Blood London for £43.75 plus the £50 blood draw, with results in 1 day.
Does a kidney check need a urine test as well as blood?
Often, yes. A urine test for protein, known as an albumin to creatinine ratio or ACR, is commonly used alongside blood tests to give a fuller picture of kidney health, since protein leaking into urine can be an early sign of kidney strain, particularly in people with diabetes or high blood pressure. Blood London offers a urine microalbumin/creatinine ratio test, with results in 1 day. The microalbumin check is also included in Diabetic Profile 2, alongside glucose and HbA1c, for anyone monitoring diabetes-related kidney risk (£161.25 plus the £50 blood draw, results in 2 days; the glucose part needs an 8-hour fast). For how these markers fit into a structured health check, see the Health Screening Clinic's guide to kidney function tests.
How kidney function testing works at Blood London
The Urea and Electrolytes (U&E) profile, which includes creatinine, costs £73.75 plus the £50 blood draw, charged once per visit. No fasting is usually needed, and results are usually back within 1 day, sent to you by email. You can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed, as part of any private blood tests in London you want done in the same visit. You can add a doctor review of your report to your test for £75. If your results sit outside the laboratory's reference range, or you develop symptoms such as persistent swelling, confusion or a marked change in urination, arrange to see a doctor promptly.
Book Urea and Electrolytes (U&E) at 117a Harley Street: £73.75 plus the £50 blood draw (£123.75 total), results in 1 day. Start your booking.
Frequently asked questions
Is eGFR a direct measurement of kidney function?
No. It is calculated from your creatinine result together with your age and sex, as an estimate rather than a direct measurement of how much blood your kidneys filter.
Can dehydration make my eGFR look worse than it is?
Yes. Dehydration can raise creatinine and lower the calculated eGFR without kidney function having actually changed, which is why hydration is worth mentioning if a result looks unexpectedly low.
How quickly will I get my kidney blood test results?
Results from the Urea and Electrolytes profile are usually back within 1 day and are sent to you by email.
Do I need to fast before a kidney blood test?
No, fasting is not usually needed for the U&E or creatinine tests, so the blood draw can be booked at any time of day.
What is the difference between creatinine and eGFR?
Creatinine is the blood measurement itself, a muscle waste product. eGFR is a calculation that uses your creatinine, age and sex to estimate overall kidney filtering.
When would a doctor want a urine test as well as a blood test?
A urine ACR test is commonly added when someone has diabetes, high blood pressure, or another reason to check specifically for protein leaking into the urine, since this can be an early sign of kidney strain.
References
- NHS: Chronic kidney disease
- NICE Clinical Knowledge Summaries: Chronic kidney disease
- NICE: Chronic kidney disease guideline (NG203)
- Kidney Care UK