Patient Guide

Complete Guide to Kidney Function Tests

Name: Complete Guide to Kidney Function Tests (KFT/RFT)
Creator: Suman Konda
Published: 2026-07-05

Kidney function tests (KFT) give a detailed picture of how well your kidneys are filtering your blood. This guide explains every test in the kidney panel.

Written by Suman Konda, PharmD, Clinical Pharmacist · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

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

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. 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

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.

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.

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

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?