What Do Your Kidney Numbers Actually Mean?

The Three Key Numbers on Every Kidney Lab Panel

Kidney function is assessed primarily through three measurements: eGFR (estimated Glomerular Filtration Rate), serum creatinine, and BUN (Blood Urea Nitrogen). These appear on standard comprehensive metabolic panels (CMP) ordered during routine physicals. Understanding what each measures helps you interpret a lab report accurately rather than waiting anxiously for a doctor's call.

eGFR is the most important number: it estimates how many milliliters of blood your kidneys filter per minute per 1.73 square meters of body surface area. A normal eGFR is above 60 mL/min/1.73m², and higher is better. eGFR above 90 is normal; 60-89 is mildly decreased but may be normal for age; 45-59 is mildly to moderately decreased; 30-44 is moderately to severely decreased; 15-29 is severely decreased; below 15 is kidney failure. A single low reading requires confirmation — eGFR fluctuates with hydration and recent protein intake.

Serum creatinine is a waste product of muscle metabolism filtered by the kidneys. Normal range is approximately 0.6-1.2 mg/dL for women and 0.7-1.3 mg/dL for men, but normal varies by age, muscle mass, and the specific lab's reference range. Higher creatinine generally means reduced kidney function. eGFR is calculated from creatinine (using age, sex, and race in the CKD-EPI formula) and is more clinically useful than creatinine alone.

Look up your kidney function stage

Enter your eGFR or creatinine value to see which CKD stage it corresponds to and what the typical next steps are.

Check My Kidney Numbers

How to Read Your Kidney Lab Values

1
Find your eGFR and identify the CKD stage
eGFR above 90: normal or high (Stage G1 if other kidney markers are abnormal). 60-89: mildly decreased (Stage G2 if other markers abnormal — often normal for older adults). 45-59: mildly to moderately decreased (Stage G3a). 30-44: moderately to severely decreased (Stage G3b). 15-29: severely decreased (Stage G4). Below 15: kidney failure (Stage G5). Stages G3 and above generally warrant nephrology involvement.
2
Check your creatinine relative to your lab's reference range
Your lab report will show both your value and the reference range. Creatinine slightly above the reference range in a person with low muscle mass (older adults, small-framed individuals) may represent more significant kidney impairment than in someone with high muscle mass — because less muscle generates less creatinine, so a normal creatinine level can mask reduced kidney function. eGFR accounts for age and sex to partially correct for this.
3
Review BUN and the BUN-to-creatinine ratio
BUN (Blood Urea Nitrogen) measures urea from protein breakdown. Normal range: 7-20 mg/dL. Elevated BUN with normal creatinine often indicates dehydration, high protein intake, or GI bleeding rather than kidney disease. The BUN-to-creatinine ratio is diagnostically useful: above 20:1 typically indicates pre-renal causes (dehydration, reduced blood flow to kidneys); ratio of 10-20:1 is normal; a low ratio may indicate liver disease or malnutrition.
4
Check for protein in urine (albuminuria)
A complete kidney assessment also includes a urine albumin-to-creatinine ratio (UACR). Normal is below 30 mg/g. Moderately increased (30-300 mg/g) or severely increased (above 300 mg/g) albuminuria alongside reduced eGFR confirms CKD and indicates kidney damage beyond filtration impairment alone. Many people have their eGFR checked but not their urine albumin — ask your provider about a complete kidney assessment if you have diabetes, hypertension, or family history of kidney disease.
5
Understand the factors that affect your numbers
eGFR decreases with age — an eGFR of 65 in a healthy 75-year-old is less concerning than the same value in a 40-year-old. Dehydration transiently raises creatinine and lowers eGFR. High protein intake (from diet or protein supplements) temporarily raises BUN and creatinine. Intense exercise raises creatinine for 24-48 hours. Certain medications (NSAIDs, some antibiotics, contrast dye) can transiently impair kidney function. Context and trends over time matter more than any single reading.

Frequently Asked Questions

What is a normal eGFR for my age?

eGFR declines with age as a normal part of aging — approximately 1 mL/min/1.73m² per year after age 40. An eGFR of 65 in a 70-year-old may represent normal age-related decline; the same eGFR in a 35-year-old is more concerning. Some age-adjusted reference ranges exist, but the standard clinical thresholds (below 60 is Stage G3+) do not adjust for age. Discuss age-related context with your provider.

Can kidney function improve if it has declined?

Depends on the cause. Acute kidney injury (AKI) — from dehydration, medication, infection — often reverses completely with treatment. Chronic kidney disease from diabetes or hypertension may slow progression significantly with excellent blood pressure and blood sugar control, but rarely reverses substantially. Early-stage CKD (G1-G2) with optimal management often remains stable for years or decades. Dietary modifications (reducing protein and sodium in advanced stages) may slow progression.

Do I need a nephrologist or can my primary care doctor manage kidney issues?

Primary care can manage early CKD (eGFR above 45) with monitoring and risk factor management. Nephrology referral is typically recommended for: eGFR below 45, rapidly declining eGFR (loss of 5+ mL/min/1.73m² in one year or 10+ over 5 years), significantly elevated albuminuria, CKD with unclear diagnosis, poorly controlled hypertension despite multiple medications, or kidney disease in pregnancy. Earlier referral allows more lead time before potential dialysis or transplant if disease progresses.

How does diabetes affect kidney numbers?

Diabetic kidney disease (diabetic nephropathy) is the leading cause of CKD in the US. Sustained high blood glucose damages the small blood vessels in the kidney glomeruli, initially causing increased protein leakage (albuminuria) before eGFR decline. People with diabetes should have both eGFR and urine albumin checked annually. Optimal blood sugar control (HbA1c below 7%), blood pressure control below 130/80, and use of kidney-protective medications (ACE inhibitors, ARBs, SGLT2 inhibitors, GLP-1 agonists) significantly slow diabetic kidney disease progression.

Is a high-protein diet bad for kidneys?

In people with normal kidney function, there is no strong evidence that high protein intake causes kidney damage. However, in people with established CKD (eGFR below 45-60), dietary protein restriction (0.6-0.8 g/kg/day) may slow progression by reducing the filtration load on damaged kidneys. For people with normal kidney function, very high protein intakes (3+ g/kg/day) may place additional filtration demands on the kidneys, but long-term harm in healthy people is not well established.

What medications are harmful to kidneys?

NSAIDs (ibuprofen, naproxen, aspirin at high doses): reduce blood flow to kidneys with regular use, particularly dangerous with existing CKD or dehydration. Contrast dye (iodinated, used in CT scans): can cause contrast-induced nephropathy, particularly in people with diabetes or pre-existing CKD — ensure adequate hydration before and after procedures. Some antibiotics (gentamicin, vancomycin at high doses): nephrotoxic. Certain chemotherapy agents. Lithium: causes gradual kidney damage with long-term use. Inform your provider of any kidney issues before any new prescription.

Understand your kidney function numbers

Enter your eGFR to see your kidney function stage and what the typical clinical guidance is.

Check My Kidney Numbers