Kidney Function Tests (KFT) Explained Step-by-Step

By Lab Decoded | Published on May 20, 2025

🧠 Why Are Kidney Tests Important?

Your kidneys are like natural filters of the body. They remove toxins, balance water and electrolytes, and help regulate blood pressure. When kidneys stop working properly, waste accumulates in the blood — leading to symptoms like swelling, fatigue, and high blood pressure. A Kidney Function Test (KFT) helps detect any signs of kidney damage early, even before symptoms start showing.

🧪 What Tests Are Included in a Kidney Function Test (KFT)?

A typical KFT panel includes the following tests:

Serum Creatinine – the most important marker of kidney filtration ability
Blood Urea Nitrogen (BUN) – measures how well kidneys remove waste
Urea – another form of nitrogen waste; high in kidney dysfunction
eGFR (Estimated Glomerular Filtration Rate) – calculated from creatinine to estimate kidney performance
Uric Acid – often elevated in kidney disease or gout
Electrolytes (Na⁺, K⁺, Cl⁻) – kidneys help maintain electrolyte balance

📊 Normal Ranges and What They Mean

Parameter	Normal Range	Clinical Significance
Serum Creatinine	Men: 0.7–1.3 mg/dL Women: 0.6–1.1 mg/dL	High levels suggest reduced kidney filtration. If rising over time, it may indicate chronic kidney disease (CKD).
Blood Urea Nitrogen (BUN)	7–20 mg/dL	Reflects waste buildup; high values may indicate poor kidney function or dehydration.
Urea	10–50 mg/dL	Produced by liver and filtered by kidneys. High urea = possible kidney stress or protein overload.
eGFR	Above 90 (Normal) Below 60 (Abnormal)	Estimated Glomerular Filtration Rate – the gold standard for assessing overall kidney function.
Uric Acid	Men: 3.4–7.0 mg/dL Women: 2.4–6.0 mg/dL	Elevated in kidney disease or gout. Can cause joint pain or kidney stones.
Sodium (Na⁺)	135–145 mmol/L	Maintained by kidneys. Imbalance may point to dehydration or kidney failure.
Potassium (K⁺)	3.5–5.1 mmol/L	Kidney dysfunction can cause potassium to rise dangerously (hyperkalemia).

🔍 Understanding eGFR: A Quick Guide</h2>
eGFR is calculated based on creatinine levels, age, gender, and sometimes race. It tells you how well your kidneys are filtering blood:

>90 – Normal kidney function

60–89 – Mild decrease (Stage 2 CKD)

30–59 – Moderate decrease (Stage 3 CKD)

15–29 – Severe decrease (Stage 4 CKD)

<15 – Kidney failure (Stage 5 CKD)

🩺 When Should You Get a KFT Done?

Consider a kidney test if you have:

Diabetes or high blood pressure
Frequent urination or difficulty urinating
Swelling in legs, feet, or face (edema)
Foamy or dark-colored urine
Family history of kidney disease
Use of nephrotoxic drugs (e.g., painkillers)

💡 Tips to Protect Kidney Health

Drink enough water (2–3 liters/day unless advised otherwise)
Limit salt, sugar, and red meat
Monitor blood pressure and blood sugar regularly
Avoid self-medication, especially painkillers or antibiotics
Exercise regularly and maintain a healthy weight

📝 Final Takeaway

Kidney Function Tests give vital clues about how well your kidneys are filtering and balancing your internal environment. Even if you feel fine, silent kidney damage may progress without warning. Timely testing, especially in high-risk individuals, can help prevent kidney failure and the need for dialysis.

Always consult your physician before making health decisions based on lab reports.