What Are Kidney Function Tests?
Kidney function tests are a group of blood tests that measure specific biomarkers to assess how well your kidneys are filtering waste products from your blood. Often referred to as a renal profile or U&E (urea and electrolytes) panel, these tests typically evaluate levels of creatinine, urea, eGFR, and key electrolytes. They are one of the most commonly requested blood panels in both NHS and private healthcare settings across the UK.
Understanding your kidney function tests can feel daunting, but the results provide valuable insight into your overall wellbeing. Whether you’ve received results you’d like to understand better or you’re considering proactive health screening at a clinic in London, this guide breaks down the key biomarkers, what they may indicate, and when testing might be worth considering.
Practical Insight: Kidney function tests are routinely included in comprehensive health screening panels and are among the most informative blood tests available for monitoring general health.
Key Biomarkers in a Kidney Function Test
A standard kidney function blood test typically measures several biomarkers. Each one provides a different piece of the picture regarding how effectively your kidneys are working.
Creatinine
Creatinine is a waste product generated by normal muscle metabolism. Healthy kidneys filter creatinine from the blood and excrete it in urine. Elevated creatinine levels can sometimes suggest that the kidneys may not be filtering as efficiently as expected. Levels can vary depending on age, sex, muscle mass, and hydration status.
eGFR (Estimated Glomerular Filtration Rate)
The eGFR is a calculated value derived from your creatinine result, age, sex, and ethnicity. It provides an estimated rate at which your kidneys filter blood. An eGFR above 90 mL/min is generally considered within the normal range, while lower values may indicate reduced kidney efficiency. It is widely used across UK healthcare as a standard measure of kidney health.
Urea (Blood Urea Nitrogen)
Urea is produced when the body breaks down protein. It is filtered by the kidneys and excreted in urine. Higher-than-expected urea levels can sometimes highlight changes in kidney function, although levels may also rise with high-protein diets or dehydration.
Electrolytes (Sodium, Potassium, Bicarbonate)
Electrolyte balance is closely regulated by the kidneys. Abnormal levels of sodium, potassium, or bicarbonate may suggest that the kidneys are having difficulty maintaining the body’s internal environment. Electrolyte imbalances can also be influenced by medications, diet, and hydration. Kidney markers are also a key component of broader screening — our guide on understanding your metabolic health panel explains how these markers fit into a wider health picture.
Practical Insight: No single biomarker tells the full story. Kidney function tests are most informative when all markers are reviewed together, ideally by a qualified healthcare professional.
Kidney Function Test: Quick Reference Comparison Table
| Biomarker | What It Measures | Typical Adult Range (Approx.) | What Changes May Suggest |
|---|---|---|---|
| Creatinine | Waste from muscle metabolism | 60–110 µmol/L (varies by sex) | Elevated levels may indicate reduced filtration |
| eGFR | Estimated kidney filtration rate | >90 mL/min (normal) | Lower values can suggest decreased kidney efficiency |
| Urea | Protein breakdown waste | 2.5–7.8 mmol/L | May rise with dehydration, diet changes, or reduced function |
| Sodium | Fluid and nerve regulation | 133–146 mmol/L | Imbalance may reflect kidney or hydration issues |
| Potassium | Heart and muscle function | 3.5–5.3 mmol/L | High or low levels can sometimes indicate kidney involvement |
| Bicarbonate | Acid-base balance | 22–29 mmol/L | Changes may suggest the kidneys are struggling to balance acidity |
*Note: Reference ranges may vary between laboratories. Always interpret results with guidance from an appropriate healthcare professional.*
What Do Your Kidney Function Test Results Mean?
Receiving your kidney function test results can raise questions, particularly if any values fall outside the standard reference range. Here is a general overview:
It is important to remember that a single blood test provides a snapshot. Trends over time are often more meaningful than isolated results, which is why periodic screening can be valuable. For a detailed breakdown of what each U&E marker means, see our guide on urea and electrolytes blood test results explained.
Practical Insight: If you’re unsure what your results mean, sharing them with a healthcare professional — such as your GP or a qualified nurse — can help you understand the next appropriate steps.
Who Should Consider Kidney Function Testing?
Kidney function tests are relevant for a wide range of individuals, not only those with existing health concerns. You may wish to consider screening if you:
Many people attending our private blood testing clinic in London choose kidney function screening as part of a broader health check, often without any specific symptoms.
Practical Insight: You don’t need to have symptoms to benefit from kidney function screening. Many kidney-related changes develop gradually and may not produce noticeable symptoms in the early stages.
How Often Should You Have Kidney Function Tests?
There is no single rule for testing frequency, as it depends on individual circumstances. General considerations include:
The NHS typically offers kidney function tests when clinically indicated, but private blood testing in London can provide convenient access without lengthy waiting times — particularly for those who prefer proactive, routine screening.
NHS vs Private Kidney Function Testing in London
| Aspect | NHS Testing | Private Blood Testing |
|---|---|---|
| Access | Requires GP referral or clinical indication | Available on a walk-in or appointment basis |
| Waiting Time | May involve waiting for appointments | Typically same-day or next-day availability |
| Results Turnaround | Can take several days to weeks | Often available within 24–48 hours |
| Cost | Free at point of care | Fee applies — check current pricing on our website |
| Scope | Based on clinical need | You can choose specific panels or comprehensive profiles |
Both pathways have their place. Private testing can complement NHS care by providing timely access to screening, particularly for individuals who wish to monitor their health between GP appointments. Our health screening services are designed to support, not replace, your ongoing relationship with your GP or medical team.
London-Based Kidney Function Screening
For residents and workers across London, accessing private kidney function tests is straightforward. At Private Blood Tests London, our nurse-led clinic offers convenient blood testing in a professional, supportive environment. Results are provided with clear, easy-to-understand reports, and we always encourage individuals to discuss any concerns with an appropriate healthcare professional.
Whether you’re based in Central London or the wider city, you can explore our full range of blood test services and book at a time that suits your schedule.
Frequently Asked Questions About Kidney Function Tests
What is included in a kidney function blood test?
A kidney function blood test typically measures creatinine, eGFR, urea, and key electrolytes such as sodium, potassium, and bicarbonate. Together, these biomarkers provide an overview of how well the kidneys are filtering waste and maintaining internal balance. The specific markers included can vary slightly depending on the laboratory and testing panel selected.
Can kidney function tests detect kidney disease early?
Kidney function tests can sometimes highlight changes in kidney efficiency before symptoms become noticeable. A reduced eGFR or elevated creatinine may suggest that further investigation is warranted. However, a single test result should always be interpreted in context, and any concerns should be discussed with an appropriate healthcare professional for further guidance.
Do I need to fast before a kidney function test?
In most cases, fasting is not required for a standard kidney function blood test. However, staying well hydrated and avoiding excessive protein intake before the test can help ensure more accurate results. If you are having additional tests alongside your renal panel, specific preparation instructions may apply — our team can advise when you book your appointment.
What does a low eGFR mean?
A low eGFR may indicate that the kidneys are not filtering blood as efficiently as expected. However, a single low reading does not necessarily confirm kidney disease. Factors including age, hydration, recent illness, and medication use can all influence eGFR. Repeat testing and clinical assessment are usually recommended to establish a clearer picture.
How long does it take to get kidney function test results?
At Private Blood Tests London, kidney function test results are typically available within 24 to 48 hours. Through the NHS, results may take longer depending on laboratory capacity and clinical prioritisation. Quick access to results can be particularly helpful for those who wish to share their findings promptly with a healthcare professional.
Are kidney function tests suitable for young adults?
Yes. While kidney function screening is more commonly associated with older adults or those with risk factors, younger individuals may also benefit — particularly if they have a family history of kidney conditions, are taking certain medications, or wish to establish a baseline for future comparison. There is no minimum age requirement for private blood testing.
Can dehydration affect kidney function test results?
Yes, dehydration can temporarily affect several kidney biomarkers, particularly creatinine and urea levels. If you are dehydrated at the time of your test, results may appear elevated even if your kidneys are functioning normally. Drinking adequate water before your test can help provide a more accurate reflection of your kidney health.
What should I do if my kidney function test results are abnormal?
If any of your results fall outside the expected range, we recommend sharing your report with a qualified healthcare professional — such as your GP — who can assess your results alongside your medical history and advise on any next steps. Our clinic provides testing and reporting only and does not offer diagnosis or treatment.
How is a kidney function test different from a urine test?
A kidney function blood test measures waste products and electrolytes circulating in the blood, while a urine test analyses substances excreted by the kidneys. Both can provide useful information about kidney health, and in some cases, healthcare professionals may recommend both for a more comprehensive assessment.
Can I get a kidney function test without a GP referral in London?
Yes. At Private Blood Tests London, you can access kidney function testing without a GP referral. Our nurse-led clinic allows you to arrange screening at your convenience. You can view available tests and book through our online booking page.
*Written: 14 March 2026 | Review date: 14 March 2027*
*This article is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Private Blood Tests London is a nurse-led screening service. We do not provide GP services, medical consultations, treatment, or prescriptions. If your results indicate areas of concern, please consult your GP or an appropriate healthcare professional.*