eGFR — the most important number

eGFR stands for estimated glomerular filtration rate. It's the single best measure of how well your kidneys are filtering your blood — and it's the number your nephrologist uses to stage your kidney disease.

Think of eGFR as a percentage of normal kidney function. A healthy young adult has an eGFR of about 100. If your eGFR is 45, your kidneys are working at roughly 45% of normal capacity.

eGFR ≥ 90 — Normal or near-normal kidney function (Stage 1 if kidney damage is present)
eGFR 60–89 — Mild reduction (Stage 2)
eGFR 30–59 — Moderate reduction (Stage 3)
eGFR 15–29 — Severe reduction (Stage 4)
eGFR below 15 — Kidney failure / ESRD (Stage 5)
eGFR naturally declines with age — even in people with healthy kidneys. An eGFR of 65 in a healthy 80-year-old may be entirely normal for their age. Your nephrologist interprets your result in context.

Serum creatinine

Creatinine is a waste product produced naturally by muscle activity. Healthy kidneys continuously filter creatinine out of the blood. When kidneys are damaged, creatinine builds up — so a higher creatinine level signals worse kidney function.

Normal creatinine levels are roughly 0.6–1.2 mg/dL for women and 0.7–1.3 mg/dL for men — but these vary by muscle mass and age. eGFR is actually calculated from creatinine (along with age and sex), which is why these two tests always appear together.

BUN (blood urea nitrogen)

BUN measures another waste product — urea — in your blood. Urea is produced when your body breaks down protein. Like creatinine, BUN rises as kidney function declines.

However, BUN is less specific than creatinine — it can also be elevated from eating a high-protein diet, dehydration, or GI bleeding, even with normal kidneys. Your doctor looks at BUN alongside creatinine to get the full picture.

UACR — urine albumin test

This urine test checks for albumin (a protein) leaking into your urine. Healthy kidneys keep protein in the blood — so protein in the urine (called proteinuria or albuminuria) is an early warning sign of kidney damage.

UACR results are classified as:

  • Normal: Less than 30 mg/g
  • Moderately increased: 30–300 mg/g (formerly called microalbuminuria)
  • Severely increased: Over 300 mg/g (formerly called macroalbuminuria or overt proteinuria)

High UACR predicts faster CKD progression — even when eGFR is still normal. It's also a strong risk factor for heart disease. ACE inhibitors and ARBs reduce proteinuria and slow kidney damage.

Other important kidney-related tests

Potassium — Kidneys regulate potassium. High potassium (hyperkalemia) can cause dangerous heart rhythm problems. Your levels will be checked regularly.
Phosphorus — Builds up in CKD and weakens bones. Managed with diet and phosphate binders.
Bicarbonate (CO2) — Measures acid-base balance. CKD often causes metabolic acidosis (blood becoming too acidic). Treated with baking soda tablets (sodium bicarbonate).
Hemoglobin / CBC — Checks for anemia, which is very common in CKD because the kidneys produce erythropoietin (EPO), a hormone that signals the bone marrow to make red blood cells.
PTH (parathyroid hormone) — Elevated in CKD due to low Vitamin D and high phosphorus. Causes bone disease if uncontrolled.
Vitamin D (25-OH) — Often deficient in CKD. Important for bone health, immune function, and possibly CKD progression.