What this test measures
A standard Indian Kidney Function Test (KFT, also called RFT) bundles together the markers a doctor needs to assess how well your kidneys are filtering blood. Core values are Serum Creatinine, Blood Urea Nitrogen (BUN), Uric Acid, the major electrolytes (Sodium, Potassium, Chloride, Bicarbonate), Calcium, Phosphorus, and the calculated estimated Glomerular Filtration Rate (eGFR).
Creatinine is a waste product of muscle metabolism — kidneys clear it at a fairly constant rate, so a rise in serum creatinine is a sensitive early signal of declining function. eGFR converts your creatinine into a percentage-style number (mL/min/1.73m²) that maps directly to chronic kidney disease (CKD) stages.
Why it matters
India has one of the highest burdens of chronic kidney disease in the world — driven by an epidemic of diabetes (the single largest cause), hypertension, NSAID overuse, and undiagnosed glomerular disease. CKD is silent in its early stages: most people have no symptoms until eGFR drops below 30, by which point the damage is largely irreversible. An annual KFT is the simplest tool to pick up early kidney disease and slow its progression with diet, blood-pressure control and medication adjustment.
A KFT is also ordered before any procedure requiring contrast dye, before starting drugs that need renal-adjusted dosing (many antibiotics, anti-diabetics, anti-virals), and as part of any workup for swelling, blood-pressure changes, fatigue, or unexplained anemia.
How to prepare
Most labs do not require fasting for a KFT, but a fasting sample (8–10 hours) is preferred when the KFT is paired with a Lipid Profile or fasting glucose. Stay well hydrated in the 24 hours before — both severe dehydration and over-hydration shift values. Avoid heavy meat consumption the day before, as a large protein meal can transiently raise urea and creatinine. Continue your regular medications unless your doctor tells you otherwise, but mention any NSAIDs, ACE inhibitors / ARBs or recent contrast scans.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Serum Creatinine (mg/dL)[1][2] | Men 0.7 – 1.3 · Women 0.6 – 1.1 | Low creatinine usually reflects low muscle mass (elderly, vegetarian diet, prolonged illness, amputation) and is not in itself concerning. Use eGFR for a more accurate read of function in low-muscle states. | A rise in creatinine signals reduced glomerular filtration. Acute rises (over hours-days) suggest acute kidney injury — dehydration, drug toxicity (NSAIDs, contrast, aminoglycosides), obstruction, or sepsis. Chronic rises (months-years) suggest chronic kidney disease (CKD). |
| Blood Urea Nitrogen (BUN) (mg/dL) | 7 – 20 | Low BUN can reflect low protein intake, severe liver disease (urea is made by the liver), or over-hydration. | High BUN can reflect reduced kidney clearance, dehydration, high-protein diet, GI bleeding (digested blood adds nitrogen), heart failure, or some drugs (steroids, tetracyclines). The BUN/Creatinine ratio (normal 10–20:1) helps separate kidney causes from pre-renal causes — ratio > 20 suggests dehydration or GI bleed. |
| eGFR (estimated Glomerular Filtration Rate) (mL/min/1.73m²)[1] | ≥ 90 normal · 60–89 mildly reduced · < 60 = CKD | Below 60 sustained for 3+ months defines chronic kidney disease (CKD). Stages: G3a (45–59) mild–moderate, G3b (30–44) moderate–severe, G4 (15–29) severe, G5 (<15) kidney failure (dialysis preparation). Each stage triggers specific monitoring and treatment. | Normal / high eGFR does not always mean no kidney disease — albuminuria can be present with normal eGFR (CKD stage 1 or 2). A urine albumin-creatinine ratio (UACR) is the missing piece if there is diabetes, hypertension or family history. |
| Potassium (mEq/L)[1] | 3.5 – 5.0 | Hypokalemia. Common causes: diuretics, vomiting, diarrhoea, low intake, magnesium deficiency, hyperaldosteronism. Symptoms: muscle weakness, cramps, palpitations. Severe (<2.5) — urgent. | Hyperkalemia. Acute kidney injury, CKD, ACE inhibitors / ARBs, spironolactone, potassium supplements, severe tissue breakdown. Above 6.0 can cause dangerous heart rhythm changes — urgent action needed. |
| Uric Acid (mg/dL) | Men 3.5 – 7.2 · Women 2.6 – 6.0 | Low uric acid is uncommon — can reflect Fanconi syndrome, SIADH, or some drugs (allopurinol, losartan). Not usually clinically meaningful. | Hyperuricaemia. Causes: high-purine diet (red meat, seafood, alcohol — especially beer), obesity, metabolic syndrome, CKD, diuretics, psoriasis. Sustained values above 6.8 risk gout (uric acid crystal arthritis) and kidney stones. |
CKD stages by eGFR (KDIGO 2024)
| Stage | eGFR range | Description | Action |
|---|---|---|---|
| G1 | ≥ 90 | Normal kidney function (CKD only if albuminuria or structural damage) | Treat underlying cause, monitor annually |
| G2 | 60 – 89 | Mildly reduced (with markers of damage = CKD) | Treat underlying cause, monitor annually |
| G3a | 45 – 59 | Mild to moderate reduction | Slow progression: BP control, ACE-i/ARB, SGLT2 inhibitor if diabetic; monitor twice yearly |
| G3b | 30 – 44 | Moderate to severe reduction | Nephrology referral, anemia + bone disease checks, monitor quarterly |
| G4 | 15 – 29 | Severe reduction | Prepare for renal replacement — vascular access, transplant evaluation |
| G5 | < 15 | Kidney failure | Dialysis or transplant required |
Frequently asked questions
Do I have to fast for a KFT?
Most labs do not require fasting for a Kidney Function Test alone. Fasting is required if the KFT is bundled with a Lipid Profile or fasting glucose. Avoid heavy meat / protein meals the night before regardless — they can transiently raise urea and creatinine.
My creatinine is 1.4 — do I have kidney disease?
A single mildly raised creatinine is not enough to diagnose kidney disease — values depend on muscle mass, age, sex and hydration. Look at the eGFR (your lab usually prints it alongside): if eGFR is below 60 and stays below 60 on a repeat test in 3 months, that meets the definition of CKD. Have your doctor interpret it together with a urine test (UACR) and blood pressure.
How often should I get a KFT?
Annually for anyone with diabetes, hypertension, family history of kidney disease, regular NSAID use, or over age 60. Every 3–6 months if you already have CKD or are on a kidney-relevant medication (ACE inhibitor, ARB, diuretic, lithium, methotrexate).
What is the difference between KFT and a "Renal Function Test"?
In Indian labs the two terms are used interchangeably. Both refer to the same panel — creatinine, urea, electrolytes, uric acid, and often eGFR. Some labs sell a "Mini" version that drops uric acid and electrolytes.
Can dehydration affect KFT results?
Yes — significant dehydration raises both urea and creatinine and gives a falsely low eGFR. This is a "pre-renal" pattern. A high BUN/Creatinine ratio (> 20) suggests dehydration rather than true kidney disease. Re-test after hydration if values are mildly off.
Will exercise affect my KFT?
Heavy exercise (especially weight training and long runs) in the 24 hours before the test can transiently raise creatinine due to muscle turnover. If you regularly do heavy exercise, mention this — chronically muscular people may have creatinine slightly above the standard reference range without any kidney disease.
My potassium is 5.5 — should I worry?
Mild hyperkalemia (5.1–5.5) is sometimes seen with delayed sample processing or hemolysis. Repeat the test promptly. If it is truly elevated and you are on an ACE inhibitor / ARB / spironolactone, your doctor may adjust the dose. Above 6.0 is potentially dangerous and needs urgent attention.
What is the role of urine tests alongside a KFT?
A KFT measures blood markers, but kidney damage can also leak protein into the urine before blood tests change. A Urine Albumin-Creatinine Ratio (UACR) or a routine urine examination picks up that earlier signal. Both tests together give the complete picture — guidelines recommend both annually for anyone with diabetes or hypertension.
Related Kidney / Electrolytes tests
Tests commonly ordered alongside Kidney Function Test (KFT), or that help interpret an unexpected result.
Sources & references
- KDIGO 2024 CKD Clinical Practice Guideline · accessed 2026-05-29T00:00:00.000Z
- National Kidney Foundation — eGFR · accessed 2026-05-29T00:00:00.000Z
- NIH MedlinePlus — Kidney Function Tests · accessed 2026-05-29T00:00:00.000Z
- ICMR Standard Treatment Workflow — Chronic Kidney Disease · accessed 2026-05-29T00:00:00.000Z
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