How to read a KFT blood test report is something millions of patients in India ask every year — and it is easy to see why. A Kidney Function Test report lands in your hands with values like Creatinine 2.4, Urea 78, eGFR 31, Potassium 5.6 and no one explains what any of it actually means or how worried you should be.

Kidney disease is one of the most silent conditions in medicine. It causes no pain, no obvious symptoms in the early stages, and by the time patients feel unwell the kidneys may already be significantly damaged. That is why the KFT is so critical — and why reading it correctly matters so much.

This guide explains every single parameter on a standard KFT report — Blood Urea, Serum Creatinine, eGFR, Uric Acid, Sodium, Potassium, Chloride, and Bicarbonate — in plain language, with real reference ranges, clinical patterns, and a full clinical scene at the end to show you how it all comes together in a real patient.

What Is a KFT Blood Test?

KFT stands for Kidney Function Test — also called RFT (Renal Function Test) or Renal Profile. It is a blood test done from a serum sample that measures how well your kidneys are filtering waste products from the blood and maintaining the body’s chemical balance.

The kidneys are ordered by almost every doctor for patients with diabetes, hypertension, heart disease, repeated urinary infections, or anyone on long-term medications like NSAIDs, ACE inhibitors, or contrast agents before a scan. If you have any of these conditions, your KFT report is one of the most important pieces of paper your doctor will review.

Blood Urea — The First Waste Marker

Urea is a waste product produced when the body breaks down protein. It is filtered out of the blood by the kidneys. When kidneys fail, urea builds up in the blood — a state called uraemia. Normal range: 15 – 45 mg/dL.

Serum Creatinine — The Most Reliable Kidney Marker

Creatinine is a waste product of normal muscle metabolism. Unlike urea, it is not affected by diet or protein intake — it is produced at a steady rate by muscles and filtered exclusively by the kidneys. This makes it the most reliable single marker of kidney filtration function on the KFT panel.

When creatinine doubles from baseline — even if still within the “normal” range on the report — it means approximately 50% of kidney function has already been lost. This is one of the most important concepts in nephrology: creatinine is a late marker. By the time creatinine becomes clearly elevated, significant kidney damage has already occurred.

eGFR — The True Measure of How Much Kidney Function Remains

eGFR stands for estimated Glomerular Filtration Rate — it tells you how many millilitres of blood the kidneys are filtering per minute per 1.73 m² of body surface area. It is calculated from the serum creatinine, age, and sex using a validated formula (usually CKD-EPI). Normal eGFR: > 90 mL/min/1.73m².

eGFR is the single most important number for staging chronic kidney disease (CKD). It translates raw creatinine into a percentage of remaining kidney function that is far more clinically meaningful.

Uric Acid — More Than Just Gout

Uric acid is a waste product formed from the breakdown of purines (found in red meat, organ meats, shellfish, alcohol, and fructose). It is filtered by the kidneys. Normal range: Male 3.5 – 7.2 mg/dL | Female 2.6 – 6.0 mg/dL.

Elevated uric acid (hyperuricaemia) is most famously associated with gout — the sudden, agonising joint pain classically affecting the big toe. But in a KFT context, a high uric acid also signals kidney stress, since failing kidneys cannot excrete it efficiently. Very high uric acid can itself damage kidneys over time — creating a vicious cycle.

Serum Electrolytes — The Body’s Chemical Balance

The kidneys are the master regulators of the body’s electrolyte balance. When kidney function deteriorates, the electrolyte panel is often where the earliest and most dangerous abnormalities appear — long before the patient feels acutely unwell.

Sodium (Na) — Normal: 135 – 145 mEq/L

Sodium is the main electrolyte controlling fluid balance outside cells. The kidneys control sodium levels precisely. Abnormal sodium is rarely about how much salt you eat — it is almost always about how the body is handling water.

• Low sodium (hyponatraemia < 135): Excess water retention, heart failure, liver cirrhosis, hypothyroidism, certain diuretics, SIADH — symptoms include confusion, nausea, seizures if severe
• High sodium (hypernatraemia > 145): Dehydration, excessive sweating, diabetes insipidus — causes intense thirst, confusion, and in extreme cases, brain damage

Potassium (K) — Normal: 3.5 – 5.0 mEq/L

Potassium is the most critical electrolyte on the KFT panel from a life-threatening perspective. It controls heart muscle rhythm. Even small deviations outside the normal range can cause fatal cardiac arrhythmias.

• Low potassium (hypokalaemia < 3.5): Vomiting, diarrhoea, diuretic use, poor intake — causes muscle weakness, cramps, irregular heartbeat
• High potassium (hyperkalaemia > 5.0): Kidney failure is the most common cause — kidneys cannot excrete potassium. Also ACE inhibitors, potassium-sparing diuretics — causes dangerous heart rhythms, can be fatal

Chloride (Cl) — Normal: 98 – 107 mEq/L

Chloride is the main negative ion in the blood that balances sodium. It generally follows sodium — when sodium rises or falls, chloride usually moves in the same direction. An isolated low chloride is seen in prolonged vomiting. It is used primarily in calculating the anion gap to assess acid-base disorders.

Bicarbonate / CO₂ — Normal: 22 – 29 mEq/L

Bicarbonate (reported as CO₂ or HCO₃) is the body’s main buffer against acid. Healthy kidneys regulate bicarbonate carefully. When kidneys fail, they cannot regenerate bicarbonate, and acid accumulates in the blood — a condition called metabolic acidosis. A low bicarbonate (<22) in a KFT report is a direct sign that the kidneys are losing their ability to maintain acid-base balance, and it worsens as CKD advances.

How to Read a KFT Report Step by Step

1. Check Creatinine first — is it above the sex-specific upper limit?
2. Look at eGFR — what stage of kidney function does this represent? (>90 = normal, <60 = CKD)
3. Compare Urea and Creatinine — are both elevated proportionally, or is urea disproportionately high? (Urea:Creatinine ratio > 40 suggests pre-renal cause — dehydration, GI bleed)
4. Check Potassium — is it above 5.5 mEq/L? If so, this is the most urgent value to act on
5. Check Sodium — is there hypo or hypernatraemia suggesting a fluid balance problem?
6. Check Bicarbonate — is it below 22? Suggests metabolic acidosis from kidney disease
7. Check Uric Acid — elevated in kidney disease and gout; treat if symptomatic
8. Trend over time — a single KFT is less valuable than comparing with a previous result. Is function stable, improving, or deteriorating?

Clinical Scene: A Patient Who Came in Feeling “Just Tired”

Rajan is a 58-year-old man with Type 2 diabetes for 12 years and hypertension on amlodipine. He comes to the medicine OPD complaining of tiredness for the past two months, mild swelling of both ankles, and “not passing much urine.” He has never had a KFT done. His doctor orders one.

The report comes back as follows:

How does the doctor read this?

Step 1 — Creatinine: 3.6 mg/dL is almost three times the upper limit of normal. This is not mild kidney impairment — this is advanced disease. The patient almost certainly had slowly rising creatinine for years while feeling perfectly fine.

Step 2 — eGFR of 19: This is CKD Stage G4 — severely decreased kidney function. Only about 20% of normal kidney capacity remains. The kidneys are struggling to do even basic filtration.

Step 3 — Potassium of 5.9: This is the most urgent finding. K above 5.5 in a CKD patient needs an immediate ECG. At 5.9, the risk of dangerous heart arrhythmia is real. This patient needs potassium restriction, medication review (stop any ACE inhibitors or potassium-sparing drugs), and possible emergency treatment before anything else.

Step 4 — Bicarbonate of 17: Below 22 confirms metabolic acidosis — the kidneys can no longer maintain the blood’s acid-base balance. This worsens bone disease, accelerates muscle wasting, and speeds up CKD progression.

Step 5 — Low Sodium: Fluid retention from failing kidneys is diluting the sodium. This explains the ankle swelling.

The full picture: Rajan has advanced diabetic nephropathy — kidney disease from 12 years of poorly controlled diabetes — now at CKD Stage G4. He almost certainly needs urgent nephrology referral, a strict potassium-restricted diet, bicarbonate supplementation, and planning for renal replacement therapy (dialysis or transplant) in the near future. All of this from one KFT report that he had never done before.

Common Mistakes When Reading a KFT Report

• Looking only at creatinine and ignoring eGFR — a creatinine of 1.2 can represent severe CKD in an elderly, frail patient with low muscle mass
• Missing a dangerous potassium level — K of 5.8 must never be dismissed as “slightly high”; it needs immediate action
• Attributing high urea to diet alone — always check creatinine to confirm whether the kidneys are actually involved
• Not asking about medications — NSAIDs, contrast dyes, ACE inhibitors, aminoglycoside antibiotics, and many herbal remedies are nephrotoxic; a raised creatinine always warrants a drug history
• Not repeating the KFT — a single elevated creatinine may be from dehydration. Rehydrate and repeat in 48–72 hours before labelling chronic kidney disease
• Ignoring low bicarbonate — it is easy to overlook a bicarbonate of 19 when creatinine looks “only mildly elevated,” but metabolic acidosis is both a consequence and a driver of CKD progression

A Note for Patients

If your KFT report has some values outside the normal range, the most important thing to know is context. A creatinine of 1.5 in a well-hydrated 30-year-old bodybuilder with large muscle mass means something very different from the same creatinine in a 70-year-old woman who has been vomiting for three days.

The values that should prompt you to seek same-day medical attention are: potassium above 6.0, creatinine more than three times your personal baseline, or significantly reduced urine output alongside a raised creatinine. Everything else deserves a calm, planned consultation with your doctor rather than panic.

And if you have diabetes or high blood pressure — please get your KFT checked every year. It is the only way to catch kidney disease before it catches you.

Summary

• KFT measures kidney waste filtration (Urea, Creatinine), filtration rate (eGFR), and electrolyte balance
• Creatinine — most reliable kidney marker; doubles = ~50% function lost; always interpret with eGFR
• eGFR — stages kidney function from G1 (normal) to G5 (kidney failure); most important number on the panel
• Blood Urea — less specific; rises with dehydration and GI bleed; interpret alongside creatinine
• Uric Acid — elevated in kidney disease and gout; >9 mg/dL warrants treatment if symptomatic
• Potassium — most dangerous electrolyte abnormality; >6.0 is a medical emergency needing urgent ECG
• Sodium — reflects fluid balance; low in kidney disease with fluid retention
• Bicarbonate — low in CKD; confirms metabolic acidosis; worsens kidney disease if untreated
• All diabetic and hypertensive patients need annual KFT — kidney disease is silent until advanced

References

1. Kidney Disease: Improving Global Outcomes (KDIGO). KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314.
2. National Institute for Health and Care Excellence (NICE). Chronic kidney disease: assessment and management. NICE guideline NG203. London: NICE; 2021.
3. Levey AS, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009;150(9):604–612. (CKD-EPI equation)
4. Inker LA, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385(19):1737–1749.
5. Indian Society of Nephrology (ISN). Indian Guidelines on Management of CKD. Indian J Nephrol. 2022;32(Suppl 1):S1–S60.
6. Mount DB. Fluid and Electrolyte Disturbances. In: Jameson JL, et al., eds. Harrison’s Principles of Internal Medicine. 21st ed. McGraw-Hill; 2022.