Kidney Function Tests: What They Measure and What Your Results Mean

Kidney function tests are blood and urine tests used to assess how well the kidneys filter waste and maintain the body’s fluid and mineral balance. Because kidney disease may develop without noticeable symptoms, these tests can identify reduced kidney function or early kidney damage before a person feels unwell.

A laboratory report may include several results, but creatinine, eGFR, and urine albumin are among the most important. Creatinine helps show how much waste is building up in the blood, eGFR estimates how efficiently the kidneys are filtering, and urine albumin can indicate damage to the kidney’s filtering units. These results are interpreted together because one abnormal number does not always indicate kidney disease.

This guide explains the main kidney function tests, what their results may mean, how to prepare for testing, and which steps can help protect kidney health.

What Do the Kidneys Do?

The kidneys filter the blood and remove waste and extra fluid through urine. They also help control blood pressure, maintain the balance of minerals such as sodium and potassium, and support the production of red blood cells.

Inside each kidney are tiny filtering structures called glomeruli. They allow waste and excess fluid to pass into the urine while keeping blood cells and most proteins in the bloodstream.

Kidney function tests look for changes caused by problems with this filtering system. Waste may build up in the blood, or a protein called albumin may begin to leak into the urine.

What Are Kidney Function Tests?

A kidney function test may refer to one test or a group of blood and urine tests ordered together. A laboratory may also call this group a renal function test, kidney function panel, or kidney profile.

The main tests include:

• Serum creatinine: Measures a waste product that healthy kidneys usually remove from the blood.
• Estimated glomerular filtration rate: Estimates how well the kidneys filter the blood.
• Blood urea nitrogen: Measures another waste product formed when the body breaks down protein.
• Urine albumin-creatinine ratio: Checks whether albumin is leaking into the urine.
• Urinalysis: Looks for blood, protein, cells, infection, and other changes in the urine.
• Cystatin C: Provides another way to estimate kidney function when creatinine may not give a reliable result.

Who Needs a Kidney Function Test?

A doctor may recommend a blood test for kidney function or urine testing if you:

• Have diabetes: High blood sugar can damage the kidney’s filtering structures over time.
• Have high blood pressure: Persistent high blood pressure can place extra strain on the kidneys.
• Have heart disease: Heart and kidney problems can affect one another.
• Have a family history: A close relative with kidney disease may increase your risk.
• Take certain medicines: Some medicines can affect the kidneys or require regular monitoring.
• Have possible symptoms: Swelling, foamy urine, blood in the urine, changes in urination, fatigue, or shortness of breath may need investigation.
• Have had an abnormal result: Repeat testing can show whether a change is temporary or persistent.

How Often Should Kidney Function Be Tested?

There is no single testing schedule for everyone. The frequency depends on your risk factors, previous results, medications, age, and whether kidney disease has already been diagnosed.

People with diabetes, high blood pressure, or known kidney disease may need regular monitoring. Your doctor will decide which tests you need and how often they should be repeated.

Blood Tests for Kidney Function

Blood tests measure waste products that the kidneys normally remove. Serum creatinine and eGFR are usually the main results used to assess how well the kidneys are filtering.

Serum Creatinine

Creatinine is a waste product produced by normal muscle activity. Healthy kidneys remove it from the blood and pass it into the urine.

A creatinine level is usually reported in mg/dL or µmol/L. The normal creatinine level varies from person to person because it is affected by age, sex, body size, and muscle mass. The reference range printed on your laboratory report is therefore more useful than a single “normal” number.

A high creatinine level may mean that the kidneys are filtering less efficiently, but it is not always caused by kidney disease. High creatinine causes can include:

• Dehydration
• Recent intense exercise
• A large amount of muscle mass
• Eating cooked meat shortly before the test
• Certain medications
• Muscle injury
• A blockage in the urinary system
• Acute or chronic kidney disease

Low creatinine causes may include low muscle mass, frailty, malnutrition, or certain long-term illnesses. A low result does not automatically mean that the kidneys are working better than expected.

The phrase creatine and kidney function often reflects confusion between creatine and creatinine. Creatine is a compound used by muscles and is also sold as a supplement. Creatinine is the waste product measured in the blood. Creatine supplements can raise creatinine slightly without causing a true reduction in kidney function, so your doctor may use cystatin C if the result is difficult to interpret.

Creatinine units may appear as mg/dL or µmol/L. Always compare your result with the unit and reference range shown on your own laboratory report.

Estimated Glomerular Filtration Rate

The estimated glomerular filtration rate, or eGFR, estimates how well your kidneys filter your blood. It is calculated mainly from your creatinine result, age, and sex.

The eGFR is often more useful than creatinine alone because the same creatinine level can have different meanings in people with different muscle mass. In general, a lower eGFR suggests reduced kidney filtration, but one low result does not confirm chronic kidney disease.

Most adult laboratories use a CKD-EPI equation to calculate eGFR. Current reporting commonly uses the 2021 CKD-EPI creatinine equation, although the method may differ between laboratories. The eGFR is still an estimate rather than a direct measurement of filtration.

An eGFR of 90 or higher is generally considered within the expected range. However, an eGFR between 60 and 89 does not automatically indicate kidney disease, especially if there are no other signs of kidney damage.

Your doctor will also consider:

• Whether the eGFR remains low over time
• Whether albumin is present in the urine
• Your age and medical history
• Your blood pressure and blood sugar
• Whether dehydration, illness, medication, or muscle mass affected the result

If creatinine may not provide a reliable estimate, your doctor may order a cystatin C test or use an eGFR calculation based on both creatinine and cystatin C.

Blood Urea Nitrogen

Blood urea nitrogen, or BUN, measures the amount of nitrogen in the blood that comes from urea. Urea is produced when the body breaks down protein and is normally removed through the kidneys.

A BUN test is often ordered with creatinine and eGFR. A typical adult BUN range is approximately 7 to 20 mg/dL, although the reference range varies between laboratories.

A high BUN may occur because of:

• Reduced kidney function
• Dehydration
• A high-protein diet
• Gastrointestinal bleeding
• Fever or severe illness
• Certain medications
• Increased breakdown of body tissue

A low BUN may occur with low protein intake, overhydration, liver disease, or malnutrition. Because diet and hydration can affect BUN, the result cannot diagnose kidney disease on its own.

The BUN-to-creatinine ratio may help your doctor interpret the results. For example, dehydration may raise BUN more than creatinine, but the ratio does not identify the cause by itself.

Cystatin C

Cystatin C is another blood marker used to estimate kidney filtration. It may be useful when creatinine is difficult to interpret because of muscle mass, diet, exercise, or supplement use.

Your doctor may consider a cystatin C test if you have:

• Very high or very low muscle mass
• Frailty or significant muscle loss
• A recent amputation
• A high level of physical activity
• Recent creatine supplement use
• A creatinine result that does not fit your overall health

Cystatin C vs. creatinine testing can provide additional information. In some cases, the doctor uses both results to calculate a combined eGFR.

Urine Tests for Kidney Function

Urine tests can detect kidney damage even when the eGFR is still within the expected range. This is important because albumin may begin to leak into the urine before the kidneys’ filtering ability declines.

Depending on the test, you may provide a single sample, an early-morning sample, or urine collected over a specified period.

Urine Albumin-Creatinine Ratio

The urine albumin-creatinine ratio, or ACR, checks whether a protein called albumin is leaking into the urine. Healthy kidneys usually keep albumin in the bloodstream, so repeated albumin in urine may indicate damage to the kidney’s filters.

The urine ACR test compares the amount of albumin with the amount of creatinine in the same sample. This helps account for whether the urine is concentrated or diluted.

The results are generally interpreted as follows:

• Below 30 mg/g: Normal to mildly increased albumin in the urine
• 30–300 mg/g: Moderately increased albumin, which may require repeat testing
• Above 300 mg/g: Severely increased albumin, which requires medical assessment

Microalbuminuria is an older term that was commonly used for an ACR between 30 and 300 mg/g. Current terminology generally refers to this as moderately increased albuminuria.

A raised ACR may be temporary. Fever, infection, intense exercise, uncontrolled blood pressure, and high blood sugar can affect the result. Your doctor may repeat the test, preferably using a first-morning urine sample, before deciding whether the change is persistent.

Urinalysis

A urinalysis examines the appearance and contents of your urine. It may involve a dipstick test, microscopic examination, or both.

It can detect:

• Protein
• Blood
• White blood cells
• Red blood cells
• Glucose
• Ketones
• Signs of infection
• Urinary casts
• Crystals

A urine protein test may measure total protein rather than albumin specifically. Protein in urine causes include kidney disease, infection, fever, dehydration, intense exercise, and pregnancy-related conditions.

Foamy urine can occur when protein is present, but it can also result from concentrated urine or rapid urination. Persistent foamy urine, especially with swelling or an abnormal ACR, should be discussed with a healthcare professional.

A urinalysis kidney disease finding does not establish the cause by itself. Additional blood tests, imaging, or specialist assessment may be required.

Understanding Kidney Function Test Results

Kidney function results should be interpreted together. The eGFR estimates how well the kidneys filter, while the ACR looks for a possible sign of kidney damage. Creatinine, BUN, urinalysis, blood pressure, symptoms, and previous results provide further context.

Chronic kidney disease is generally diagnosed when reduced kidney function or another sign of kidney damage remains present for at least three months. A single abnormal result may instead be related to dehydration, infection, intense exercise, medication, or another short-term problem.

What Does Your eGFR Result Mean?

Your eGFR appears as a number on the laboratory report. In general:

• An eGFR of 90 or higher is usually within the expected range
• An eGFR between 60 and 89 may indicate mildly reduced filtration, but it does not usually confirm kidney disease on its own
• An eGFR between 45 and 59 may indicate a moderate reduction and usually requires follow-up
• An eGFR between 30 and 44 indicates a more significant reduction and generally requires closer monitoring
• An eGFR between 15 and 29 indicates severely reduced kidney function and requires specialist care
• An eGFR below 15 falls within the kidney failure range and requires urgent specialist assessment

You may see labels such as G1, G2, G3a, G3b, G4, or G5 on a medical report. These are professional categories used to describe the eGFR ranges above. They are not separate tests, and you do not need to interpret them without the actual number and your doctor’s explanation.

A low eGFR meaning cannot be determined from the number alone. The result must be considered alongside your age, previous tests, urine ACR, symptoms, and other medical information.

What Does Your ACR Result Mean?

The ACR shows how much albumin is present in the urine:

• Below 30 mg/g: Normal to mildly increased
• 30–300 mg/g: Moderately increased
• Above 300 mg/g: Severely increased

You may see the labels A1, A2, or A3 on the report. These are simply professional terms for the three ranges above. A result in the A2 or A3 range does not automatically confirm permanent kidney disease, but it does require appropriate follow-up.

Typical Creatinine and BUN Ranges

Reference ranges vary between laboratories and depend on age, sex, muscle mass, and the testing method. Typical adult ranges may include:

• Serum creatinine: Approximately 0.6–1.2 mg/dL, or about 53–106 µmol/L, in many adults
• BUN: Approximately 7–20 mg/dL in many adult laboratories
• ACR: Less than 30 mg/g is generally considered normal to mildly increased

Always use the reference range printed on your own report. A result outside that range does not automatically confirm kidney disease, and a result within the range does not rule out every kidney problem.

What Can Cause an Abnormal Result?

Abnormal kidney function test results do not always indicate permanent kidney disease. Your doctor may compare the result with previous tests and look for temporary explanations, including:

• Dehydration
• Fever or infection
• Strenuous exercise
• A recent meal containing cooked meat
• Certain medications
• Creatine or high-protein supplements
• A temporary urinary blockage

Your doctor may recommend repeating the test, reviewing medication and supplement use, or ordering additional tests. These may include cystatin C, more detailed urine testing, or a kidney ultrasound.

A kidney ultrasound can show the size and structure of the kidneys and may identify a blockage. A kidney biopsy is used only in selected cases when a small sample of kidney tissue is needed to determine the cause of damage.

When to Seek Prompt Medical Attention

Seek prompt medical care if you have an abnormal kidney result and develop:

• Markedly reduced or absent urine
• Rapidly increasing swelling
• Severe shortness of breath
• Confusion or extreme drowsiness
• Chest pain
• Severe weakness
• Repeated vomiting
• Blood in the urine with severe pain or illness

These symptoms may indicate acute kidney injury, fluid overload, a urinary blockage, or another condition requiring urgent treatment.

How to Prepare for a Kidney Function Test

Most kidney function tests do not require fasting. Fasting may be necessary if your doctor orders other tests, such as blood glucose or cholesterol, at the same time.

Before testing:

• Drink normally: Maintain your usual fluid intake unless your doctor has restricted fluids
• Avoid unusual exercise: Intense physical activity can affect creatinine and some urine results
• Mention recent meals: Tell the healthcare professional if you recently ate a large amount of cooked meat
• Report supplements: Mention creatine, protein supplements, vitamins, and herbal products
• List your medications: Include prescription medicines and over-the-counter pain relievers
• Follow urine instructions: Some tests require an early-morning sample or a timed collection
• Do not stop prescribed medicines independently: Change medication only on your doctor’s advice

A 24 hour urine test requires you to collect every urine sample during a specified period. For routine albumin screening, a single urine ACR sample is often sufficient.

Can You Improve Kidney Function?

Established chronic kidney damage usually cannot be reversed, but treatment can often slow further decline and protect the kidney function that remains. Kidney function affected by acute kidney injury can sometimes recover when the cause—such as dehydration, infection, medication, or a urinary blockage—is treated promptly.

There is no reliable detox product or supplement that can repair damaged kidneys. The most effective approach is to identify the cause, manage conditions that affect the kidneys, use medication correctly, and attend follow-up appointments.

Protecting the Kidneys You Have

A kidney-friendly lifestyle should be tailored to your test results and overall health.

• Control blood pressure: Take prescribed treatment and monitor your blood pressure as recommended
• Manage blood sugar: If you have diabetes, keeping blood glucose within the target range can reduce kidney damage
• Use pain relievers carefully: Frequent use of NSAIDs, including ibuprofen and naproxen, can harm the kidneys, particularly during dehydration or illness
• Maintain appropriate hydration: Drink according to your doctor’s advice, especially if you have heart disease or advanced kidney disease
• Follow individualized dietary advice: Foods for kidney health depend on your eGFR, potassium, phosphorus, protein needs, and other conditions
• Avoid smoking: Smoking increases the risk of kidney and cardiovascular disease
• Stay physically active: Avoiding a sedentary lifestyle and engaging in regular physical activity can support healthy blood pressure, blood sugar, weight, and heart health

How to lower creatinine depends on why it is elevated. Treating dehydration or stopping an interfering supplement may change the result, but a high creatinine level caused by kidney disease requires medical evaluation rather than a quick dietary solution.

Why Choose Medical Park for Kidney Function Tests?

Medical Park Hospitals provide kidney function tests in Turkey for international patients seeking routine screening, further assessment after abnormal results, a second opinion, or evaluation of a known kidney condition. Before the appointment, the medical team can review previous laboratory results, imaging, medical history, and current medications to determine which tests and specialist consultations may be appropriate.

Depending on the patient's needs, testing may include serum creatinine, eGFR, BUN, cystatin C, urine albumin-creatinine ratio, urinalysis, electrolyte testing, and other investigations. Blood tests provide information about kidney function and related health factors, while urine tests can detect albumin, protein, blood, and other changes that may indicate kidney damage.

Kidney function testing may be arranged as part of preventive health screenings or a broader check-up. When symptoms or test results suggest a urinary tract problem, such as an obstruction or kidney stone, further evaluation may include imaging.

Depending on the findings, patients may be assessed by specialists in Nephrology, Urology, Internal Medicine, and other relevant departments. A nephrologist can evaluate persistent changes in kidney function, albuminuria, electrolyte abnormalities, or suspected acute or chronic kidney disease, while urological assessment may be appropriate when urinary obstruction, kidney stones, or other structural problems are suspected.

Further testing may include repeat blood or urine tests, kidney ultrasound, or other imaging depending on the initial findings. Reviewing the results with the appropriate specialist can help determine whether an abnormal result is temporary or reflects an ongoing kidney problem and whether further investigation or treatment is needed.

For international patients, Medical Park's International Patient Services Center helps coordinate consultations, diagnostic appointments, hospital arrangements, interpretation, and communication with the relevant departments. Following the evaluation, the medical team explains the results, discusses any recommended follow-up, and helps the patient understand the next steps in their care.