Complete Guide to Kidney Function Tests (KFT/RFT)

Quick answer

Kidney function is tracked mainly through creatinine, eGFR (which corrects for age, sex and muscle mass) and urine protein, with potassium watched closely since failing kidneys retain it dangerously. The core takeaway: a single low eGFR does not diagnose chronic kidney disease, which needs persistent abnormality over three months, and many common drugs need dose changes as kidney function falls.

Complete kidney function test panel

Test	Normal Range	What it measures
Creatinine	Men: 0.74–1.35 mg/dL; Women: 0.59–1.04 mg/dL	Waste product from muscle: rises as kidneys fail
eGFR	≥60 mL/min/1.73m²	Estimated kidney filtering rate: most important kidney measure
Blood Urea / BUN	7–20 mg/dL	Protein waste product: also raised in dehydration and bleeding
Uric Acid	Men: 3.5–7.2 mg/dL; Women: 2.6–6.0 mg/dL	Gout risk: also rises in kidney disease
Sodium	136–145 mEq/L	Fluid balance: regulated by kidneys
Potassium	3.5–5.0 mEq/L	Critical electrolyte: dangerously high in kidney failure
Bicarbonate	22–29 mEq/L	Acid-base balance: low in CKD (metabolic acidosis)
Phosphorus	2.5–4.5 mg/dL	Rises in CKD: causes bone disease
Calcium	8.5–10.5 mg/dL	Bone and parathyroid: affected in CKD
Urine ACR	<30 mg/g	Kidney protein leakage: earliest sign of damage

Key points

eGFR (not creatinine alone) is the key measure; it corrects for age, sex and muscle mass.
CKD needs persistent abnormality over 3 months, not one low reading.
Staging runs G1 to G5 by eGFR plus urine protein.
Watch potassium: failing kidneys retain it, and levels above 6.0 mEq/L are dangerous.
Many drugs need dose adjustment as kidneys decline.

Why eGFR matters more than creatinine

The problem with creatinine alone

Creatinine depends on muscle mass: a young muscular man and an elderly frail woman with the same creatinine have vastly different kidney function. eGFR (estimated GFR) corrects for age, sex and race to give a more accurate kidney function estimate. eGFR below 60 on two tests at least 3 months apart = chronic kidney disease.¹ eGFR can appear falsely normal even when significant kidney damage has occurred, urine ACR (protein test) is needed to detect early kidney disease when eGFR is still above 60.

Why potassium is critical in kidney disease

Healthy kidneys excrete excess potassium in urine. As kidneys fail, potassium accumulates in the blood (hyperkalaemia). Potassium above 6.0 mEq/L causes dangerous heart arrhythmias and can be fatal. People with CKD need to monitor potassium regularly and may need to limit high-potassium foods (bananas, potatoes, tomatoes, oranges) and avoid medications that raise potassium (ACE inhibitors, ARBs, potassium-sparing diuretics).

CKD staging: what the eGFR number means

A single low eGFR does not diagnose chronic kidney disease (CKD). The international standard, the 2012 KDIGO (Kidney Disease: Improving Global Outcomes) clinical practice guideline, requires two readings below the threshold at least three months apart, because a temporary fall in eGFR can occur with dehydration, acute illness, or NSAID use.¹ The eGFR threshold of 60 itself isn't an arbitrary round number: a KDIGO-sponsored meta-analysis of 45 cohorts and more than 1.5 million participants found that the risk of kidney failure and death rises once eGFR falls below this level, which is why the definition was set there.³

KDIGO Stage	eGFR (mL/min/1.73m²)	Description
G1	≥90	Normal or high, CKD only if urine ACR or structural abnormality present
G2	60–89	Mildly decreased, CKD only if kidney damage markers present
G3a	45–59	Mildly to moderately decreased
G3b	30–44	Moderately to severely decreased
G4	15–29	Severely decreased, specialist referral, transplant planning
G5	<15	Kidney failure, dialysis or transplantation

Each stage is also categorised by urine ACR: A1 (<30 mg/g, normal to mildly increased), A2 (30–300 mg/g, moderately increased), or A3 (>300 mg/g, severely increased). A person with eGFR 60 but ACR above 300 mg/g has a substantially worse prognosis than the eGFR alone would suggest. The combined GFR-ACR classification is now the standard way to communicate CKD severity and guide monitoring frequency.²

Drugs that need special caution in kidney disease

Many medicines are cleared by the kidneys and accumulate to toxic concentrations when renal function falls. As a clinical pharmacist, reviewing drug safety against kidney function is among the most frequent practical tasks in managing patients with CKD.

Metformin: dose reduced at eGFR 30–45; stopped below eGFR 30, lactic acidosis risk rises steeply in severe CKD
NSAIDs (ibuprofen, naproxen, diclofenac): suppress renal prostaglandins, reduce kidney blood flow, and can trigger acute kidney injury, avoid in eGFR below 30 and use with caution above 30
ACE inhibitors and ARBs: slow CKD progression and reduce proteinuria, but raise potassium; always check potassium and creatinine 1–2 weeks after starting or up-titrating
Nitrofurantoin: ineffective and potentially toxic below eGFR 45; it accumulates in the urine only when kidneys work well enough
Direct oral anticoagulants (DOACs): apixaban, rivaroxaban, edoxaban and dabigatran are all renally cleared to varying degrees; dose adjustment or avoidance is required below eGFR thresholds specific to each drug

Telling every prescriber and pharmacist your current eGFR is a simple habit that prevents a wide range of drug-related kidney injuries and toxicity.

Questions to ask your kidney doctor

What is my eGFR stage, and how quickly is it declining?
Do I have significant proteinuria on my urine ACR?
Is my potassium safe?
Do I need dietary restrictions for my kidney disease?
Am I on any medications that could harm my kidneys?

Your next steps for understanding your kidney results

Look at eGFR, not creatinine alone
Creatinine depends on muscle mass: the same value means very different things in a young muscular man and a frail older woman. eGFR corrects for age and sex, so it is the number that stages kidney health.
Check your potassium
Failing kidneys retain potassium, and levels above 6.0 mEq/L can trigger dangerous heart arrhythmias. Potassium safety is one of the first things your doctor assesses alongside eGFR.
Confirm before you worry about CKD
Chronic kidney disease requires eGFR below 60 on two readings at least three months apart — a single low reading never diagnoses it. Ask whether the result was repeated over time.
Review your medications
Many drugs — from metformin and NSAIDs to some antibiotics and blood thinners — need dose adjustment or avoidance as kidneys decline. Telling every prescriber your current eGFR prevents a wide range of drug-related injuries.
Don’t forget the urine test
A urine albumin-to-creatinine ratio under 30 mg/g is normal; leakage above that is the earliest sign of kidney damage, appearing years before eGFR falls. Ask whether yours has been checked.

Kidney function test panel at a glance

The kidney panel measures both what the kidneys filter and the electrolytes they regulate. eGFR is the headline number; the rest add context and safety.

Test	Normal range	What it measures
Creatinine	Men 0.74–1.35 mg/dL; women 0.59–1.04 mg/dL	Muscle waste product; rises as kidneys fail
eGFR	≥60 mL/min/1.73m²	Estimated filtering rate; the most important kidney measure
Blood urea / BUN	7–20 mg/dL	Protein waste; also raised in dehydration and bleeding
Uric acid	Men 3.5–7.2; women 2.6–6.0 mg/dL	Gout risk; rises in kidney disease
Sodium	136–145 mEq/L	Fluid balance, regulated by the kidneys
Potassium	3.5–5.0 mEq/L	Critical electrolyte; dangerously high in kidney failure
Bicarbonate	22–29 mEq/L	Acid-base balance; low in CKD
Urine ACR	<30 mg/g	Protein leakage; earliest sign of kidney damage

Practical notes

Ask your doctor whether to avoid heavy exercise and very high-protein meals for a day or two before creatinine and eGFR testing — both can nudge creatinine upward. Drink normally: dehydration concentrates the blood and can make results look worse than they are.

Bring a complete medicine list, including over-the-counter painkillers and supplements — several common drugs affect kidney markers or need dose review when kidneys are impaired. Disclose everything, but never stop or change a medicine on your own.

Read eGFR for what it is: an estimate, not a measurement. It moves with age, muscle mass, and hydration, and a urine albumin result alongside it tells a fuller story than either alone. Ask your doctor what your trend looks like, not just today's number.

For follow-up, ask how often to repeat — stable patients often recheck every 6–12 months on their doctor's plan — what would trigger sooner testing, and which symptoms (swelling, reduced urine, unusual fatigue) warrant a call between visits.

In India

A basic kidney function test panel (KFT/RFT) is typically ₹600–₹1,500; adding a urine albumin test pushes the total modestly higher, though prices vary by city and lab. Ask exactly which tests are included before you pay.

Choose NABL-accredited labs, and note that home sample collection is available in major cities. The reference range printed on your own report is the one that counts — eGFR in particular is reported using method-specific equations that differ between labs.

Frequently Asked Questions

Why does eGFR matter more than creatinine?

Creatinine depends on muscle mass: a young muscular man and an elderly frail woman with the same creatinine have vastly different kidney function. eGFR corrects for age and sex to give a more accurate estimate. An eGFR below 60 on two tests at least three months apart is what raises the question of chronic kidney disease — one reading never does.

Why is potassium so critical in kidney disease?

Healthy kidneys excrete excess potassium in urine. As kidneys fail, potassium accumulates in the blood, and levels above 6.0 mEq/L can cause dangerous heart arrhythmias and can be fatal. People with chronic kidney disease need to monitor potassium regularly and may need to limit high-potassium foods — discuss your level with your doctor.

What do the CKD stages mean?

The KDIGO stages run G1 to G5 by eGFR: G1 (≥90) and G2 (60–89) are only CKD if urine albumin or structural damage is also present; G3a (45–59) and G3b (30–44) are mildly to severely decreased; G4 (15–29) needs specialist referral and transplant planning; G5 (below 15) is kidney failure, requiring dialysis or transplantation. Each stage is further graded by urine ACR.

Which medicines need special caution in kidney disease?

Many medicines are cleared by the kidneys and accumulate to toxic levels when function falls — reviewing drug safety against kidney function is one of a clinical pharmacist's most frequent tasks. Examples include NSAIDs like ibuprofen, which can trigger acute kidney injury, and metformin, which is stopped below eGFR 30. Always tell every prescriber and pharmacist your current eGFR.

My creatinine is normal — does that mean my kidneys are fine?

Usually reassuring, but not the whole story. Creatinine can stay normal while early kidney damage is already underway, which is why doctors also look at eGFR trends and urine albumin. If you have diabetes, high blood pressure, or a family history of kidney disease, ask whether urine testing is part of your monitoring.

Can I take painkillers if my kidney numbers are borderline?

Be cautious and ask your doctor or pharmacist first. Common painkillers such as NSAIDs can strain the kidneys, especially with dehydration or other risk factors. Describe what you take and how often, and get guidance on safer options for your situation.

Does drinking more water improve my eGFR?

Good hydration keeps results accurate, but water does not fix kidney function — and overdoing fluids can be harmful if the kidneys are already impaired. Drink normally before the test and follow your doctor's fluid guidance rather than a self-set target.

How often should kidney tests be repeated?

It depends on your risk and prior results — people with diabetes, hypertension, or known kidney issues typically recheck more often than healthy adults. Your doctor sets the interval; ask at each visit when the next check is due and what would bring it forward.

References

Sources cited on this page. PubMed links open the original abstract.

Stevens PE, Levin A; Kidney Disease: Improving Global Outcomes CKD Guideline Development Work Group Members. Evaluation and management of chronic kidney disease: synopsis of the kidney disease: improving global outcomes 2012 clinical practice guideline. Ann Intern Med. 2013;158(11):825–830. PMID 23732715 · doi:10.7326/0003-4819-158-11-201306040-00007
Levey AS, Eckardt KU, Dorman NM, et al. "Nomenclature for kidney function and disease: report of a Kidney Disease: Improving Global Outcomes (KDIGO) Consensus Conference." Kidney Int. 2020;97(6):1117–1129. PMID 32409237 · doi:10.1016/j.kint.2020.02.010
Levey AS, de Jong PE, Coresh J, et al. "The definition, classification, and prognosis of chronic kidney disease: a KDIGO Controversies Conference report." Kidney Int. 2011;80(1):17–28. PMID 21150873 · doi:10.1038/ki.2010.483

Medical Disclaimer: For educational purposes only. Always consult a qualified healthcare professional for diagnosis and treatment.