Kidney Function Blood Tests: eGFR, Creatinine & Monitoring CKD

Why Kidney Function Testing Matters

Your kidneys filter approximately 180 litres of blood every day, removing waste products, balancing electrolytes, regulating blood pressure, and producing hormones that control red blood cell production. When kidney function declines, waste products build up in the blood and essential functions are compromised.

Chronic kidney disease (CKD) is remarkably common in the UK, affecting around 3.5 million people. The condition often develops silently — most people with early CKD have no symptoms at all. By the time symptoms appear, significant and often irreversible damage has occurred. This is why blood testing is so important: it can detect kidney problems long before you feel unwell.

eGFR (Estimated Glomerular Filtration Rate)

eGFR is the most important number on a kidney function test. It estimates how much blood your kidneys filter per minute, based on your blood creatinine level, age, sex, and ethnicity. It is reported in ml/min/1.73m².

• 90 or above — Normal kidney function (CKD stage 1 if other markers of kidney damage are present).
• 60 to 89 — Mildly reduced function (CKD stage 2). Often age-related, especially in older adults.
• 45 to 59 — Mild to moderately reduced (CKD stage 3a).
• 30 to 44 — Moderately to severely reduced (CKD stage 3b).
• 15 to 29 — Severely reduced (CKD stage 4). Referral to a nephrologist is recommended.
• Below 15 — Kidney failure (CKD stage 5). Dialysis or transplant may be needed.

A single low eGFR does not necessarily mean CKD. The diagnosis requires two results below 60, taken at least 3 months apart, to confirm a sustained decline in function.

Creatinine

Creatinine is a waste product produced by your muscles as they break down creatine phosphate for energy. Healthy kidneys filter creatinine out of the blood efficiently. When kidney function declines, creatinine levels rise.

Normal creatinine ranges are approximately 60 to 110 µmol/L for men and 45 to 90 µmol/L for women, though this varies by laboratory. Creatinine is also influenced by muscle mass, diet (particularly red meat intake), and hydration, so it is always interpreted alongside eGFR rather than in isolation.

Urea

Urea is a waste product formed when the liver breaks down protein. Like creatinine, it is filtered by the kidneys. Raised urea levels can indicate reduced kidney function, but urea is also affected by dietary protein intake, dehydration, gastrointestinal bleeding, and certain medications. The normal range is approximately 2.5 to 7.8 mmol/L.

Electrolytes: Sodium and Potassium

The kidneys play a vital role in maintaining the balance of electrolytes in your blood. Two of the most important are:

• Sodium (Na+) — Normal range 133 to 146 mmol/L. The kidneys regulate sodium to control blood pressure and fluid balance. Abnormal levels can cause confusion, seizures, or muscle weakness.
• Potassium (K+) — Normal range 3.5 to 5.3 mmol/L. The kidneys are the primary route for potassium excretion. In CKD, potassium can rise to dangerous levels, potentially causing cardiac arrhythmias. This is one reason why regular monitoring is critical in advanced CKD.

Who Should Have Kidney Function Tests?

NICE recommends regular kidney function testing for anyone with risk factors, including:

• Diabetes — The most common cause of CKD in the UK. People with diabetes should have annual kidney checks including eGFR and urine albumin-to-creatinine ratio (ACR).
• High blood pressure — Hypertension damages the small blood vessels in the kidneys over time.
• Cardiovascular disease — Heart and kidney health are closely linked.
• Family history of CKD or kidney failure.
• Regular use of NSAIDs (such as ibuprofen) or other nephrotoxic medications.
• Age over 60 — Kidney function naturally declines with age.

How Often Should You Be Monitored?

The frequency of kidney function tests depends on the stage of CKD, as set out in NICE guideline CG182:

• CKD stages 1 and 2 — Annually.
• CKD stage 3 — Every 6 months.
• CKD stages 4 and 5 — Every 3 months or more frequently if unstable.

More frequent testing may also be needed if you start a new medication that affects kidney function, such as ACE inhibitors, ARBs, or diuretics.

Do Kidney Tests Require Fasting?

Standard kidney function blood tests (U&Es and eGFR) do not require fasting. You can eat and drink normally before the test. However, avoid eating a large high-protein meal immediately before the test, as this can temporarily elevate urea levels.

Getting Tested at Home

If you need regular kidney function monitoring, having your blood taken at home can make the process much more manageable. A qualified mobile phlebotomist from Lola Dispatch can visit you at a convenient time, collect the necessary samples, and send them to an accredited laboratory. This is especially valuable for CKD patients who may have mobility difficulties or need frequent monitoring.

All Lola Dispatch phlebotomists are DBS-checked and experienced in routine monitoring bloods. Book a home blood test to skip the waiting room and keep on top of your kidney health.