What blood tests check kidney function in the UK? 

In the UK, the primary blood test used to check kidney function is the creatinine test, which is then used to calculate your estimated Glomerular Filtration Rate (eGFR). Because the kidneys are responsible for filtering waste and excess fluid from the blood, measuring the levels of specific waste products provides a clear picture of how efficiently they are working. These tests are standard across the NHS and are often performed alongside an electrolyte panel to check levels of sodium, potassium, and urea. 

What We Will Cover in This Article 

• Understanding the role of Serum Creatinine in renal assessment. 

• How the eGFR calculation determines your percentage of kidney function. 

• The importance of the Urea test and what high levels indicate. 

• The role of Electrolyte monitoring (Sodium and Potassium) for kidney safety. 

• How these tests are used to ‘stage’ Chronic Kidney Disease (CKD). 

• What to expect during your blood test appointment at a GP surgery. 

• Factors that can temporarily affect your kidney test results. 

The Primary Marker: Serum Creatinine 

Creatinine is a chemical waste product produced by your muscle metabolism. Under normal conditions, healthy kidneys filter creatinine from your blood and pass it out through your urine. If your kidneys are not functioning at their full capacity, the level of creatinine in your blood will begin to rise. 

A Serum Creatinine test measures the exact amount of this waste in your bloodstream. While it is a vital marker, it is important to note that creatinine levels can be influenced by your age, sex, and muscle mass. For instance, a very muscular person may have a higher ‘normal’ level than a smaller, less active individual. This is why the NHS uses this result to calculate a more personalized score called the eGFR. 

• Filtration Check: High creatinine usually indicates the kidneys are struggling to clear waste. 

• Consistency: Clinicians look for stable or changing levels over several months. 

• Clinical Context: Your doctor will always interpret creatinine in relation to your overall health. 

Understanding Your eGFR Result 

The estimated Glomerular Filtration Rate (eGFR) is arguably the most important number in kidney health. Instead of just looking at raw creatinine, the eGFR uses a formula to estimate how many millilitres of blood your kidneys are filtering every minute. In the UK, a result of 90 or above is generally considered normal function. 

The eGFR is used to categorize kidney health into five distinct stages. If your eGFR stays below 60 for more than three months, it typically confirms a diagnosis of Chronic Kidney Disease (CKD). This helps your clinical team decide how often you need to be monitored and whether you need specific treatments to protect your renal function. 

eGFR Result	What it Means	Clinical Action
90 or above	Normal kidney function	Routine monitoring if risk factors exist.
60 to 89	Mildly decreased function	Check for other signs like protein in urine.
30 to 59	Moderately decreased function	Regular GP reviews and blood pressure control.
15 to 29	Severely decreased function	Likely referral to a kidney specialist (nephrologist).
Below 15	Kidney failure	Discussion of advanced treatments (dialysis/transplant).

Urea and Electrolyte Panels (U&Es) 

When you have a ‘kidney test’ in the UK, it is usually requested as a U&E (Urea and Electrolytes) panel. This group of tests provides a broader view of your metabolic health and how your kidneys are managing the body’s chemical balance. 

Urea is another waste product, formed when the liver breaks down protein. High urea levels can indicate kidney trouble, but they can also be raised by dehydration, a high-protein diet, or certain medications. Alongside urea, the lab will check your Potassium and Sodium levels. The kidneys are essential for keeping these in a very narrow, safe range; if potassium levels become too high (hyperkalaemia), it can affect heart rhythm and requires urgent clinical attention. 

• Sodium: Helps regulate fluid balance and blood pressure. 

• Potassium: Vital for muscle and heart function. 

• Urea: A secondary marker of filtration and hydration status. 

Factors That Can Affect Your Results 

It is important to remember that a single blood test is a ‘snapshot’ in time. Several everyday factors can cause your creatinine or eGFR to fluctuate temporarily. If your results are unexpected, your GP will often ask for a repeat test in a few weeks to ensure the reading was accurate and not influenced by external factors. 

Common factors that may impact results include: 

• Dehydration: Lack of fluids can temporarily raise creatinine and lower eGFR. 

• Recent Exercise: Intense weightlifting can cause a temporary spike in creatinine levels. 

• Diet: Consuming a large amount of cooked meat within 24 hours of the test. 

• Medications: Some drugs, such as certain antibiotics or stomach acid tablets, can interfere with the test. 

To Summarise 

In the UK, kidney health is primarily assessed using the Serum Creatinine test and the calculated eGFR score. These tests, often performed as part of a U&E panel, allow clinicians to determine how well your kidneys are filtering waste and balancing essential electrolytes like potassium. By monitoring these markers over time, the NHS can identify kidney issues early, allowing for proactive care to protect your long-term health. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot 

This article outlines the standard clinical blood tests used by the NHS to monitor renal function, following established NICE and UK health frameworks. Dr. Rebecca Fernandez, a UK-trained physician with experience in internal medicine, emergency medicine, and cardiology, has reviewed this content. Her background in interpreting complex diagnostic results and managing acute and chronic illness ensures that this information is medically accurate and emphasizes the role of clinical testing in renal preservation.