What is a normal eGFR?

An eGFR of 90 or higher is considered normal. A sustained eGFR between 60 and 89 indicates mild kidney damage, and anything below 60 for more than three months indicates chronic kidney disease (CKD).

Why would my BUN to Creatinine ratio be high?

A high BUN-to-Creatinine ratio (typically >20:1) is most commonly caused by severe dehydration or decreased blood flow to the kidneys (such as in heart failure). A normal ratio is between 10:1 and 20:1.

Does eating a lot of meat increase creatinine?

Yes, eating large amounts of cooked red meat or taking creatine supplements for muscle building can cause a temporary spike in blood creatinine levels, which may falsely mimic decreased kidney function.

Creatinine, eGFR & BUN — Understanding Kidney Function Tests

The Body's Filtration System

Your kidneys are twin bean-shaped organs that act as your body's master filtration system. Every day, they filter about 200 quarts of blood, removing waste products and excess water (which becomes urine) while returning essential chemicals to the bloodstream. When kidney function declines, dangerous levels of waste and fluid can build up in the body. Because early kidney disease often has no symptoms, routine blood tests are the only way to catch a decline in function before it becomes severe.

What Markers Are Measured?

A standard Renal (Kidney) Panel evaluates several chemicals in the blood to determine how efficiently the kidneys are filtering waste:

1. Serum Creatinine

Creatinine is a chemical waste product generated by normal muscle wear and tear. Healthy kidneys filter almost all creatinine out of the blood and into the urine. Therefore, if blood creatinine levels are high, it is a primary indicator that the kidney's filtration system is impaired.

2. eGFR (Estimated Glomerular Filtration Rate)

This is the most critical number on a kidney panel. It is not directly measured; rather, it is a mathematically calculated score based on your creatinine level, age, and gender. The eGFR represents the filtration rate of the kidneys. An eGFR of 90 means your kidneys are working at roughly 90% capacity.

3. BUN (Blood Urea Nitrogen)

When your liver breaks down proteins from the food you eat, it produces urea nitrogen as a waste product, which is then sent to the kidneys for excretion. High BUN levels indicate the kidneys are struggling to clear this waste. However, BUN is easily influenced by other factors (like high-protein diets or dehydration), so it is always evaluated alongside creatinine.

Understanding the Results

Kidney function is typically staged based on the eGFR result:

Stage 1 (Normal): eGFR > 90 (with no other signs of kidney damage, like protein in the urine).
Stage 2 (Mild decline): eGFR 60 to 89.
Stage 3a/3b (Moderate decline): eGFR 30 to 59. This requires active medical management to slow progression.
Stage 4 (Severe decline): eGFR 15 to 29.
Stage 5 (Kidney Failure): eGFR less than 15. Requires dialysis or a kidney transplant.

Common Causes of Kidney Damage

The two leading causes of chronic kidney disease (CKD) are poorly controlled diabetes (high blood sugar damages the blood vessels in the kidneys) and high blood pressure (which exerts damaging force against the kidneys' delicate filters). Other causes include prolonged use of NSAID pain relievers (like ibuprofen), autoimmune diseases (like lupus), and recurrent kidney infections.

When to Be Concerned

Dehydration can cause temporary spikes in creatinine and BUN. However, if your eGFR drops below 60 on two separate tests spaced a few months apart, you have Chronic Kidney Disease. This requires strict management of blood pressure and blood sugar to protect remaining kidney function. You should immediately discuss lifestyle modifications and medication reviews with a nephrologist.

Creatinine, eGFR & BUN: Understanding Kidney Function Tests