Kidney Function Tests
KFT / RFT / BMP
Kidney function tests (also called renal function tests or RFTs) assess how well the kidneys are filtering waste products from the blood. The key measurements include serum creatinine, estimated glomerular filtration rat...
About this Test
Kidney function tests (also called renal function tests or RFTs) assess how well the kidneys are filtering waste products from the blood. The key measurements include serum creatinine, estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), and urine albumin/creatinine ratio. These tests are essential for detecting chronic kidney disease (CKD), monitoring patients with diabetes or hypertension, and adjusting medication doses for kidney-excreted drugs.
Why is this test ordered?
- Suspected kidney disease (swelling, reduced urine output, foamy urine)
- Monitoring diabetes or hypertension (leading causes of CKD)
- Pre-surgical kidney function assessment
- Monitoring nephrotoxic medications (NSAIDs, ACE inhibitors, metformin)
- Evaluation before contrast imaging (CT scan dye)
- Electrolyte abnormalities (high potassium, low sodium)
- Routine health check-up in adults over 50
- Family history of kidney disease
How to Prepare
- β’Fasting for 8 hours recommended for BUN accuracy (though not always required)
- β’Stay well hydrated β dehydration can temporarily elevate creatinine
- β’Avoid intense exercise for 24 hours before test (can raise creatinine)
- β’Inform doctor of all medications β many affect kidney markers
- β’A high-protein meal before testing can temporarily elevate BUN
The Procedure
Blood is drawn from a vein in the arm. The laboratory measures creatinine, BUN/urea, and electrolytes (sodium, potassium, bicarbonate). eGFR is calculated from creatinine, age, sex, and race using the CKD-EPI or MDRD formula. A urine sample may also be collected to measure protein/albumin in urine. Results are typically available within 24 hours.
Normal Reference Ranges
Serum Creatinine: 0.7β1.3 mg/dL (men), 0.5β1.1 mg/dL (women). eGFR: β₯ 90 mL/min/1.73mΒ² (normal). 60β89 (mildly reduced). 30β59 (CKD stage 3). < 30 (severe CKD). BUN (Blood Urea Nitrogen): 7β20 mg/dL. Urine albumin/creatinine ratio: < 30 mg/g normal.
Reference ranges may vary between laboratories. Always interpret results with your doctor.
Interpreting Your Results
When results are HIGH
High creatinine and low eGFR indicate reduced kidney function (CKD). High BUN with high creatinine = kidney failure. High BUN with normal creatinine = dehydration or high protein intake. Elevated urine albumin indicates early kidney damage (diabetic nephropathy). Hyperkalemia (high potassium) is a serious complication of advanced CKD.
When results are LOW
Low creatinine may indicate reduced muscle mass (elderly, malnutrition). Low BUN may indicate liver disease, malnutrition, or overhydration. Low eGFR is always concerning and warrants nephrology referral if persistently below 60 mL/min.
Frequently Asked Questions
What is eGFR and what does it tell me?
eGFR (estimated Glomerular Filtration Rate) estimates how many milliliters of blood your kidneys filter per minute per 1.73mΒ² of body surface area. An eGFR above 90 is normal. Below 60 for 3+ months indicates chronic kidney disease (CKD). The lower the eGFR, the more advanced the kidney disease. An eGFR below 15 may require dialysis or kidney transplantation.
Can exercise affect kidney function test results?
Yes. Intense exercise increases creatinine production from muscle breakdown, temporarily raising serum creatinine and lowering calculated eGFR. This is a normal physiological effect, not kidney damage. Avoid strenuous exercise for 24 hours before kidney function testing to get accurate baseline results.
When should I see a nephrologist (kidney specialist)?
See a nephrologist if your eGFR is persistently below 60 mL/min, if you have significant protein in your urine, if kidney function is declining rapidly, if you have unexplained kidney disease, or if you need evaluation for kidney stones or structural abnormalities. Your GP can provide initial assessment and refer you.
Quick Reference
- Test name
- Kidney Function Tests
- Abbreviation
- KFT / RFT / BMP
- Category
- Nephrology
- Turnaround
- 24 hours for standard laboratory testing.
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