Kidney Function Tests: Creatinine, BUN, and GFR Explained

Understanding Kidney Function Tests

Kidney function tests assess how well your kidneys are filtering waste from the blood. These tests are essential for detecting kidney disease early and monitoring chronic conditions like diabetes and hypertension. Early intervention can prevent progression to kidney failure.

Key Kidney Function Markers

1. Creatinine

A waste product produced by muscles. Healthy kidneys filter creatinine into urine for excretion. Elevated creatinine indicates reduced kidney function. Normal levels are 0.6-1.2 mg/dL for men and 0.5-1.1 mg/dL for women.

2. Blood Urea Nitrogen (BUN)

A waste product from protein metabolism. Kidneys filter BUN into urine. Elevated BUN (normal: 7-20 mg/dL) can indicate kidney disease but also dehydration or high protein intake.

3. Glomerular Filtration Rate (GFR)

Measures how much blood the kidneys filter per minute. GFR is calculated from creatinine levels and is the best indicator of kidney function. Normal GFR is 90 mL/min/1.73m² or higher.

4. Electrolytes (Sodium, Potassium, Chloride)

Kidneys regulate electrolyte balance. Abnormal levels can indicate kidney dysfunction and require immediate medical attention.

5. Urine Albumin

Albumin in urine (proteinuria) suggests kidney damage. It's an early sign of kidney disease and requires investigation and treatment.

Stages of Chronic Kidney Disease

• ✓ Stage 1: GFR ≥ 90 (Normal or high)
• ✓ Stage 2: GFR 60-89 (Mildly decreased)
• ✓ Stage 3a: GFR 45-59 (Mildly to moderately decreased)
• ✓ Stage 3b: GFR 30-44 (Moderately to severely decreased)
• ✓ Stage 4: GFR 15-29 (Severely decreased)
• ✓ Stage 5: GFR < 15 (Kidney failure/End-stage renal disease)

Risk Factors for Kidney Disease

Diabetes, hypertension, family history of kidney disease, advanced age, obesity, and smoking significantly increase kidney disease risk. Regular screening is recommended for high-risk individuals.

When Should You Get Kidney Function Tests?

Kidney function tests are recommended for routine checkups, in patients with diabetes or hypertension, if experiencing fatigue or edema, before starting certain medications, and when evaluating abnormal urinalysis results.

Preparation and Testing

A simple blood draw and urinalysis are required. No special preparation is needed, though you may be asked to avoid excessive protein intake the day before testing. Results are typically available within 24 hours.