Creatinine and eGFR: Decoding Your Kidney Health Tests

Kidney health is vital for overall well-being, yet often overlooked until problems arise. Two key tests—creatinine levels and estimated glomerular filtration rate (eGFR)—serve as critical indicators of kidney function. This guide breaks down what these tests mean, why they matter, and how to interpret your results for proactive health management.

What is Creatinine?

Creatinine is a waste product generated by muscles during normal metabolism. It’s produced at a relatively constant rate and filtered almost exclusively by the kidneys. Measuring creatinine levels in blood or urine provides insight into how well your kidneys are working.

Key Facts:

Source: Derived from creatine phosphate (a muscle energy compound).
Production: Higher in people with more muscle mass.
Excretion: Healthy kidneys efficiently remove creatinine from the blood.

The Creatinine Test

A serum creatinine test measures the amount of creatinine in your blood. Results are reported in milligrams per deciliter (mg/dL) or micromoles per liter (µmol/L).

Normal Ranges:

Group	Normal Blood Creatinine
Adult Men	0.7–1.3 mg/dL
Adult Women	0.6–1.1 mg/dL
Children	0.3–0.7 mg/dL

Note: Ranges vary slightly between labs.

What Abnormal Results Mean:

High Creatinine:
- Possible Causes: Kidney damage, dehydration, urinary tract obstruction, muscle injury, or certain medications (e.g., NSAIDs, chemotherapy).
- Symptoms: Swelling, fatigue, shortness of breath, or changes in urine output.
Low Creatinine:
- Often linked to low muscle mass (e.g., aging, malnutrition) or pregnancy.

What is eGFR?

Estimated Glomerular Filtration Rate (eGFR) calculates how much blood your kidneys filter per minute (measured in mL/min/1.73m²). Unlike creatinine alone, eGFR accounts for age, sex, race, and body size, offering a more accurate snapshot of kidney function.

How eGFR is Calculated:

eGFR uses your creatinine level, age, sex, and race in standardized formulas like:

CKD-EPI Equation: Most common (recommended by guidelines).
MDRD Equation: Older but still used.

Example: A 50-year-old White man with creatinine of 1.0 mg/dL has an eGFR of ~90 mL/min/1.73m².

eGFR Stages (Chronic Kidney Disease Classification):

eGFR (mL/min/1.73m²)	Stage	Kidney Function
≥90	G1	Normal
60–89	G2	Mildly reduced
45–59	G3a	Mild-moderate loss
30–44	G3b	Moderate-severe loss
15–29	G4	Severely reduced
<15	G5	Kidney failure

Why Combine Creatinine and eGFR?

Creatinine alone is insufficient: It doesn’t reflect kidney function in people with very high/low muscle mass.
eGFR contextualizes results: Adjusts for individual factors to detect early kidney disease.
Early detection matters: eGFR identifies CKD before symptoms appear, enabling timely intervention.

Causes of Abnormal eGFR

Low eGFR (<60 mL/min/1.73m²):
- Diabetes, hypertension, glomerulonephritis, or recurrent kidney infections.
High eGFR (>120 mL/min/1.73m²):
- Early diabetes, pregnancy, or hyperfiltration (can precede kidney damage).

How to Improve Kidney Health

Control Blood Sugar & Blood Pressure: Leading causes of CKD.
Hydrate Wisely: Drink water but avoid excess fluid if advised.
Limit Nephrotoxic Substances: NSAIDs (e.g., ibuprofen), heavy metals, and contrast dyes.
Adopt a Kidney-Friendly Diet:
- Reduce sodium, processed meats, and phosphorus (in sodas, processed foods).
- Moderate protein intake (excess strains kidneys).
Exercise Regularly: Supports healthy weight and blood pressure.

When to Get Tested

The National Kidney Foundation recommends screening if you have:

Diabetes or hypertension.
Family history of kidney disease.
Symptoms like persistent swelling or fatigue.
Adults over 60 should discuss annual testing with their doctor.

FAQs About Creatinine & eGFR

Q: Can dehydration affect creatinine levels?

A: Yes! Dehydration concentrates blood, raising creatinine. Always hydrate before testing.

Q: Is eGFR reliable for everyone?

A: Not for extremes—e.g., bodybuilders (high muscle mass) or amputees (low muscle mass). Cystatin C testing may supplement eGFR here.

Q: Can eGFR improve?

A: Yes! Managing diabetes/hypertension, quitting smoking, and dietary changes can stabilize or slow decline.

Q: What if my eGFR is 50?

A: Stage G3a CKD. Work with a nephrologist to address underlying causes and protect remaining function.

Q: Are at-home kidney tests accurate?

A: Blood-based tests require labs. Urine test strips screen for protein/blood but don’t replace eGFR.

Creatinine and eGFR are lifelines for monitoring kidney health—a silent powerhouse of your body. Regular testing is crucial for early detection of kidney disease, especially if you have risk factors. Don’t wait for symptoms; discuss these tests with your doctor today. Healthy kidneys today ensure vitality tomorrow!