Kidney Function Tests Explained

What Do Your Kidneys Do?

Your kidneys are two bean-shaped organs that filter about 200 quarts of blood daily, removing waste products and excess fluid, regulating blood pressure, balancing electrolytes, and producing hormones for red blood cell production and bone health.

Key Kidney Markers

A basic metabolic panel typically includes these kidney markers.

• Creatinine — A waste product from muscle metabolism. Rises when kidney function declines. Normal: 0.7–1.3 mg/dL (men), 0.6–1.1 mg/dL (women).
• BUN (Blood Urea Nitrogen) — A waste product from protein metabolism. Normal: 7–20 mg/dL.
• eGFR (Estimated Glomerular Filtration Rate) — The best overall measure of kidney function. Normal is 90 or above. Below 60 for 3+ months indicates chronic kidney disease.
• BUN/Creatinine Ratio — Helps distinguish kidney problems from other causes. Normal: 10:1 to 20:1.

Understanding eGFR Stages

eGFR estimates how many milliliters of blood your kidneys filter per minute.

• 90+ — Normal kidney function.
• 60–89 — Mildly decreased (Stage 2). Often no symptoms.
• 30–59 — Moderate decrease (Stage 3).
• 15–29 — Severely decreased (Stage 4).
• Below 15 — Kidney failure (Stage 5). May require dialysis.

What Can Affect Your Results

Several factors can temporarily affect kidney markers without indicating actual disease.

• Dehydration — Can raise both BUN and creatinine.
• High-protein diet — Can temporarily raise BUN.
• Intense exercise — Can temporarily raise creatinine.
• Medications — NSAIDs and certain antibiotics can affect markers.
• Age — Kidney function naturally declines slightly with age.

Protecting Your Kidney Health

Many of the same habits that protect your heart also protect your kidneys.

• Stay well hydrated — aim for 6 to 8 glasses of water daily.
• Manage blood pressure — a leading cause of kidney disease.
• Control blood sugar — diabetes is the other leading cause.
• Limit NSAID use — regular use can damage kidneys over time.
• Get regular checkups — early detection is key.