WHAT IS THE NORMAL RANGE FOR KIDNEY FUNCTION TEST?

Kidney function tests are commonly used to check how well the kidneys are working, but receiving a result can be confusing if you are unsure what is considered normal. Many people are told their kidney function is slightly reduced or borderline without a clear explanation of what the numbers mean or whether there is cause for concern.

Understanding the normal ranges helps put results into context and explains why factors such as age, hydration and overall health are taken into account.

Because early changes in kidney function do not always cause symptoms, blood testing plays a key role in identifying potential issues. A Kidney Function Blood Test from One Day Tests allows you to measure important markers such as eGFR and creatinine and better understand how your kidneys are functioning before reading further into what the results may show.

Kidney function tests are used to assess how effectively the kidneys filter waste products and regulate fluid and electrolyte balance in the body. The most important measure of kidney function is the estimated glomerular filtration rate, known as eGFR.

eGFR is calculated using a blood marker called creatinine along with age and sex. Creatinine is a waste product produced from normal muscle breakdown and protein digestion. Healthy kidneys remove creatinine from the bloodstream efficiently. When kidney function declines, creatinine levels rise and eGFR falls.

Kidney function blood tests usually also include markers such as urea, sodium and potassium. These substances are regulated by the kidneys and can become abnormal when kidney function is impaired. Some test panels may also include chloride, albumin and total protein.

Blood tests alone do not provide a complete picture of kidney health. Urine testing is often needed to check for protein or blood, which may indicate kidney damage even when blood results appear within normal ranges.

There is no single normal kidney function result that applies to everyone. eGFR results are interpreted using ranges that help classify kidney health and identify chronic kidney disease if present.

An eGFR above 90 is considered normal kidney function. However, if blood or protein is detected in the urine, this may still be classified as chronic kidney disease stage 1.

An eGFR between 60 and 89 is generally considered satisfactory and is very common, particularly in people over the age of 60. If urine abnormalities are present alongside this range, it may be classified as chronic kidney disease stage 2.

An eGFR between 30 and 59 indicates reduced kidney function and is classed as chronic kidney disease stage 3. This stage is often divided into stage 3a, which ranges from 45 to 59, and stage 3b, which ranges from 30 to 44.

An eGFR between 15 and 29 is classified as chronic kidney disease stage 4 and represents significant kidney impairment. People at this stage are usually reviewed by a kidney specialist.

An eGFR below 15 is classified as chronic kidney disease stage 5, also known as end stage kidney disease. At this point, dialysis may be considered depending on overall health and symptoms.

Creatinine levels vary depending on sex and muscle mass. People with higher muscle mass naturally produce more creatinine, which can make kidney function appear lower than it truly is. Conversely, people with low muscle mass may have lower creatinine levels, which can make kidney function appear better than it is.

Urea is another waste product measured in kidney function tests. Raised urea levels can indicate reduced kidney function, but they may also increase due to dehydration or high protein intake.

Electrolytes such as sodium and potassium are tightly regulated by the kidneys. When kidney function declines, these levels may become abnormal and require monitoring, particularly potassium, as high levels can affect heart rhythm.

Kidney function naturally declines with age, especially after the age of 60. This does not always mean there is underlying kidney disease, but results should be interpreted carefully in older adults.

Hydration status has a significant impact on kidney test results. Dehydration can temporarily lower eGFR and raise urea levels, sometimes mimicking kidney disease or acute kidney injury.

Certain medications can influence kidney function results. Trimethoprim can cause a temporary fall in eGFR without true kidney damage. Non steroidal anti inflammatory drugs can reduce blood flow to the kidneys. ACE inhibitors and ARBs may cause a small initial drop in eGFR that is often expected and monitored. Diuretics can affect electrolyte levels.

Chronic conditions such as diabetes, high blood pressure, high cholesterol and autoimmune disease are common contributors to reduced kidney function over time.

A single kidney function result does not always reflect true kidney health. Short term changes can occur due to illness, dehydration, medication changes or infection.

Doctors usually assess kidney function by looking at trends over time. A stable eGFR that remains unchanged for years is often less concerning than a sudden decline, even if the number itself appears within a similar range.

Repeat testing is commonly used to confirm whether a result represents a true change in kidney function or a temporary fluctuation.

Persistently abnormal kidney function results should always be discussed with a doctor. Further testing may include repeat blood tests, urine analysis or imaging to assess kidney structure.

Symptoms of kidney disease are often vague and may include persistent fatigue, nausea, reduced appetite, swelling, increased urination, excessive thirst, shortness of breath or persistent itching without a rash.

Because early kidney disease often causes no symptoms, blood testing is the most reliable way to identify kidney problems before complications develop.

If you want to check your kidney health proactively or monitor existing kidney function, a Kidney Function Blood Test from One Day Tests can assess key markers such as eGFR, creatinine and electrolytes and help identify potential issues early.

The normal range for kidney function tests is based primarily on eGFR, with values above 90 considered normal and lower ranges used to classify stages of chronic kidney disease. Results must always be interpreted in context, taking into account age, muscle mass, hydration, medications and long term trends.

Blood tests combined with urine testing provide the most accurate assessment of kidney health and help guide appropriate monitoring and treatment when needed.