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Kidney Test

Kidney Function Test (KFT / RFT)

KFT measures waste products in your blood to assess how well your kidneys are filtering. Here's what creatinine, urea and eGFR values mean for you.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

What is a KFT test?

A Kidney Function Test (KFT), also called Renal Function Test (RFT), measures waste products that healthy kidneys should be removing from your blood. When kidneys are damaged or not working well, these waste products build up. KFT is used to diagnose chronic kidney disease (CKD), monitor diabetic or hypertensive kidney damage, and check kidney health before starting certain medications.

Chronic kidney disease stages by eGFRThe six eGFR categories used to stage chronic kidney disease.Kidney function stages by eGFRmL/min/1.73m². G1 and G2 only count as kidney disease with evidence of damageStageeGFRMeaningG1≥90Normal †G260–89Mildly reduced †G3a45–59Mild to moderateG3b30–44Moderate to severeG415–29Severely reducedG5<15Kidney failure† G1 and G2 are only kidney disease if urine or imaging also shows damage. eGFR 90+ with a normal urine test is normal.
Scroll sideways to see the whole diagram
eGFR categories used to stage chronic kidney disease.
What the chart shows. Kidney function is graded by eGFR from G1 at 90 or above down to G5 below 15. An important qualification: the top two grades are not by themselves chronic kidney disease. G1 and G2 only count as kidney disease when there is also evidence of damage, such as albumin in the urine, blood in the urine, or a structural abnormality on imaging, and the finding has persisted for at least three months. An eGFR of 95 with a normal urine test is a normal result, not stage G1. From G3a downwards the reduction in filtration is itself sufficient. Stage is also only half the picture, because the same eGFR carries a materially higher risk of progression when albumin is leaking, which is why an albumin-to-creatinine ratio is measured alongside.

KFT Normal Range Chart

TestNormal RangeUnit
Serum Creatinine: Men0.74 – 1.35mg/dL
Serum Creatinine: Women0.59 – 1.04mg/dL
Serum Creatinine: Women0.5 – 1.1mg/dL
Blood Urea Nitrogen (BUN)7 – 20mg/dL
Serum Urea15 – 45mg/dL
Uric Acid: Men3.5 – 7.2mg/dL
Uric Acid: Women2.6 – 6.0mg/dL
eGFR (kidney filtration rate)Above 90mL/min/1.73m²
Sodium136 – 145mEq/L
Potassium3.5 – 5.0mEq/L

What does high creatinine mean?

HIGH Creatinine above normal

High creatinine means your kidneys are not filtering waste efficiently. Common causes include dehydration, chronic kidney disease (CKD), diabetes-related kidney damage (diabetic nephropathy), high blood pressure, or certain medications. Mildly raised creatinine with dehydration usually normalises after drinking water. Persistently high creatinine needs investigation.

What does low eGFR mean?

LOW eGFR below 60

eGFR (estimated Glomerular Filtration Rate) shows how much blood your kidneys filter per minute. Below 60 for 3+ months indicates Chronic Kidney Disease (CKD). The lower the eGFR, the more severe the kidney damage: eGFR 30–59 = moderate CKD; eGFR 15–29 = severe; below 15 = kidney failure requiring dialysis or transplant.

What does high uric acid mean?

HIGH Uric Acid above normal

High uric acid (hyperuricaemia) causes gout: painful swollen joints, especially the big toe. It also increases risk of kidney stones. Common triggers include high-purine foods (red meat, shellfish, offal), excess alcohol, dehydration and obesity. Low-purine diet and medication can control it.

Diabetes, BP and kidneys

Diabetes and high blood pressure are the two biggest causes of kidney failure worldwide. If you have either condition, KFT should be done at least once a year. Early kidney damage (Stage 1–2 CKD) has no symptoms but can be detected by KFT and urine microalbumin test. Catching it early can stop or slow progression.

What kidney function tests measure

Kidney function tests assess how well your kidneys filter waste from the blood. Creatinine, a waste product from muscles, is the core measurement, and from it the laboratory calculates the eGFR (estimated glomerular filtration rate): the best single indicator of kidney function. Urea and electrolytes such as sodium and potassium are usually reported too.

An eGFR above 90 is generally normal, while a value persistently below 60 for more than three months indicates chronic kidney disease, graded in stages by how low it falls.

Why the urine test matters too

Blood tests alone can miss early kidney damage. The urine albumin-to-creatinine ratio (ACR) detects small amounts of protein leaking into the urine, often the first sign of damage, appearing before eGFR declines. This is especially important in people with diabetes or high blood pressure, the two leading causes of kidney disease.

Combining blood and urine tests therefore gives a much earlier and more complete picture of kidney health.

What affects kidney results

Creatinine and eGFR can be influenced by muscle mass, dehydration, a very high-protein meal and certain medicines, so a single abnormal result is often repeated. Because eGFR is an estimate, trends over time are more meaningful than one reading.

Protecting the kidneys centres on controlling blood pressure and diabetes, staying hydrated, and reviewing medicines that can affect the kidneys, such as some painkillers.

Frequently Asked Questions

Do I need to fast for a kidney function test?
No fasting is needed, though avoiding a very large protein meal and vigorous exercise beforehand helps give a representative creatinine result.
What is eGFR?
eGFR estimates how much blood your kidneys filter each minute. Above 90 is normal; below 60 for over three months indicates chronic kidney disease.
Can kidney damage exist with normal blood tests?
Yes. Early damage often shows first as protein in the urine, which is why the urine ACR test matters alongside blood tests.
Is a single abnormal result serious?
Not necessarily: dehydration, diet, muscle mass and medicines can affect results, so abnormal readings are usually repeated to confirm a genuine trend.

References

The clinical information on this page is based on peer-reviewed sources indexed in PubMed, the biomedical literature database of the US National Library of Medicine.

  1. Grams ME, Coresh J, Matsushita K, et al.. Estimated glomerular filtration rate, albuminuria, and adverse outcomes: an individual-participant data meta-analysis. JAMA. 2023;330(13):1266-1277. doi:10.1001/jama.2023.17002 · PMID 37787795

Related reading

Medical Disclaimer: Creatinine levels vary with muscle mass, age and hydration. A single elevated result does not always mean kidney disease. This information is for educational purposes only. Always consult your nephrologist or physician regarding your kidney function test results.