Key takeaways
- eGFR is worked out from your creatinine, age and sex, as an estimate of how well your kidneys are filtering.
- Muscle mass, a recent meaty meal, hard exercise and hydration can all move creatinine while your kidneys stay exactly as they were.
- Chronic kidney disease is diagnosed on results that stay low over at least three months. After one low reading, a repeat test is the usual next step.
- A urine test for protein, called ACR, often sits alongside the blood test for a fuller kidney check.
Your eGFR has come back a little low, perhaps with a note to repeat it. Or you have a creatinine figure and an eGFR side by side and no idea how they relate.
eGFR estimates how well your kidneys are filtering waste from your blood. It is calculated from your creatinine level together with your age and sex. The Urea and Electrolytes (U&E) profile at Blood London measures creatinine alongside urea and the main blood salts, with no GP referral needed.
If you would rather get tested than read on, book a Urea and Electrolytes (U&E) test at 117a Harley Street. It costs £73.75 plus the £50 blood draw (£123.75 total), with results in 1 day.
What does eGFR actually measure?
eGFR is a calculation. Laboratories put your creatinine result, age and sex into a standard formula to estimate how much blood your kidneys filter each minute. It stands in for a more complex, invasive measurement, and it is the figure doctors use most to judge overall kidney function.
A lower eGFR generally means the kidneys are filtering less well. Several everyday factors can shift the number, though, without any real change in kidney health.
What is creatinine, and why does it matter alongside eGFR?
Creatinine is a waste product of muscle activity, cleared from the blood by the kidneys. Its level reflects both how much muscle you have and how well your kidneys clear it. People with more muscle tend to have a naturally higher creatinine. The eGFR formula adjusts for age and sex, but it has no way to allow for muscle mass itself.
A recent meaty meal, intense exercise or dehydration can all raise creatinine for a while and lower the calculated eGFR. That 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, 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 can all move your creatinine, and your calculated eGFR with it. Certain medicines can also affect creatinine, so mention anything you take when your blood is drawn.
This is why a one-off low eGFR is usually followed by a repeat test. It is also why NICE advises avoiding meat in the 12 hours before an eGFR test.
| 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?
Not on its own. Chronic kidney disease is defined by results that stay reduced when the test is repeated over at least three months. If your eGFR comes back low, the usual next step is a repeat test after a short interval. Your hydration, recent diet and any medicines are reviewed at the same time.
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. It is sometimes checked alongside creatinine as part of a wider assessment. A raised urate can be linked to gout, and kidney function affects how well urate is cleared. Urate (uric acid) can be booked as a standalone test for £43.75, 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, gives a fuller picture of kidney health. 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 for £100, with results in 1 day. It is a urine sample, so there is no blood draw fee.
The microalbumin check is also part of Diabetic Profile 2, with glucose and HbA1c, for anyone monitoring diabetes-related kidney risk. It costs £161.25, with results in 2 days, and the glucose part needs an 8-hour fast. For how these markers fit into a structured health check, see the Health Screening Clinic guide to kidney function tests.
How kidney function testing works at Blood London
You can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed. Fasting is not usually needed. Results are usually back within 1 day and sent to you by email.
Each blood test price on this page is plus the £50 blood draw, which is charged once per visit. The urine ACR test has no blood draw fee. That makes it easy to add other private blood tests in London at the same time. You can also add a doctor review of your report for £75.
If your results sit outside the reference range, arrange to see a doctor. Do the same promptly if you develop persistent swelling, confusion or a marked change in urination. When you are ready, start your booking.
Frequently asked questions
Is eGFR a direct measurement of kidney function?
It is an estimate. eGFR is calculated from your creatinine result together with your age and sex.
Can dehydration make my eGFR look worse than it is?
Yes. Dehydration can raise creatinine and lower the calculated eGFR while kidney function stays the same. It 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?
Fasting is not usually needed for the U&E or creatinine tests, so you can come in at any time of day.
What is the difference between creatinine and eGFR?
Creatinine is the blood measurement itself, a muscle waste product. eGFR 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 for protein leaking into the urine. 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