Kidney Tests Explained: Creatinine, eGFR, Urine ACR & Electrolytes
Understanding kidney function starts with the right lab tests. Creatinine, eGFR, urine albumin‑to‑creatinine ratio (uACR) and electrolyte panels are the four pillars doctors use to spot early disease, track progression, and guide treatment. This guide breaks down each test, normal values, and what the numbers mean for you.
Kidneys filter waste, balance fluids, and regulate electrolytes. When they falter, waste builds up, blood pressure spikes, and vital minerals become imbalanced. Early detection through lab testing can prevent irreversible damage and reduce the need for dialysis or transplant.
If you notice any of these, ask your primary‑care physician for a kidney panel.
Creatinine is a waste product from muscle metabolism. The kidneys clear it from the blood, so higher levels indicate reduced filtration. Normal ranges vary by sex and muscle mass, but typical limits are 0.6–1.2 mg/dL for women and 0.7–1.3 mg/dL for men Nephrology Specialists. Values above these thresholds often signal early kidney stress.
eGFR translates the creatinine value into an estimate of how many milliliters of blood the kidneys filter each minute per 1.73 m² of body surface. An eGFR > 60 mL/min/1.73 m² is generally considered normal, 30–59 suggests moderate decline, and <30 indicates severe kidney disease MyNephrologist. The calculation also incorporates age, sex, and sometimes race, making it a more comprehensive indicator than creatinine alone.
Albumin is a protein that should stay in the bloodstream. When the glomeruli are damaged, albumin leaks into urine. uACR compares the amount of albumin to creatinine in a single urine sample, eliminating the need for a 24‑hour collection. Normal uACR is 300 mg/g reflects macro‑albuminuria (significant damage) MyNephrologist. This test can detect kidney injury years before eGFR drops.
Electrolyte panels measure sodium, potassium, chloride, bicarbonate, and calcium—minerals the kidneys tightly regulate. Abnormalities often accompany chronic kidney disease (CKD). BUN, another waste product, rises as kidney function declines but is less specific than creatinine because it is influenced by diet and hydration Nephrology Specialists.
Because eGFR is derived from creatinine, the two numbers should be read as a pair. A mildly elevated creatinine with a normal eGFR may be due to high muscle mass, while a normal creatinine with a low eGFR often points to early CKD, especially in older adults.
Even with a healthy eGFR, a uACR > 30 mg/g signals that the kidney’s filtering units are leaking protein. This early sign is common in diabetes and hypertension and warrants tighter blood‑sugar or blood‑pressure control, plus possible referral to a nephrologist.
High potassium (hyperkalaemia) can indicate reduced excretion, while low sodium often reflects fluid overload. Metabolic acidosis (low bicarbonate) is another hallmark of advanced CKD. Spotting these changes early allows dietary or medication adjustments before complications arise.
If any of the following appear, schedule a consultation with a kidney specialist:
Our clinic’s nephrology team can provide a detailed assessment and personalized plan. Learn more about when to see a specialist in When Should You See a Nephrologist in Navi Mumbai?.
Use this quick reference during your next lab visit:
| Kidney Test | Typical / Reference Range | When to Seek Medical Attention |
|---|---|---|
| Serum Creatinine | Reference ranges vary by laboratory, age, sex, and muscle mass. | A persistently elevated or rising creatinine level may require further evaluation. |
| eGFR | Generally ≥60 mL/min/1.73 m² | An eGFR below 60 that persists for 3 months or longer may indicate chronic kidney disease. |
| Urine ACR (uACR) | <30 mg/g | 30–300 mg/g indicates moderately increased albuminuria; >300 mg/g indicates severely increased albuminuria. |
| Electrolytes (Na, K, Cl, HCO₃) |
Within your laboratory's reference range | Persistent or significant abnormalities, particularly potassium or bicarbonate changes, require medical assessment. |
| BUN | Typically about 7–20 mg/dL, depending on the laboratory | An elevated BUN should be interpreted together with creatinine, eGFR, hydration status, and other clinical findings. |
Regular monitoring—typically every 6–12 months for at‑risk patients—helps catch changes early. For detailed guidance on test frequency, see our When Is Dialysis Needed? Symptoms, eGFR & Clinical Factors page.
By understanding what each number represents, you can partner with your healthcare team to protect kidney health before problems become serious.
Kidney tests measure waste removal (creatinine, eGFR), protein leakage (uACR), and mineral balance (electrolytes). Together they reveal how well the kidneys filter blood and whether early damage is present.
The urine albumin‑to‑creatinine ratio (uACR) is the most sensitive early marker, often detecting damage before eGFR declines. Serum creatinine and eGFR confirm overall filtration capacity.
Persistent fatigue, swelling, changes in urine, high blood pressure, and unexplained muscle cramps should trigger a kidney panel, including creatinine, eGFR, uACR, and electrolytes.
Creatinine provides the raw waste level, while eGFR translates it into an estimated filtration rate adjusted for age, sex, and body size. A high creatinine with a normal eGFR may be due to muscle mass; a low eGFR with normal creatinine often signals early CKD.
See a nephrologist if eGFR falls below 60 mL/min/1.73 m², uACR is ≥30 mg/g, electrolytes stay abnormal, or creatinine rises rapidly. Early referral improves outcomes.
Myths include believing a normal creatinine rules out disease, that only diabetics need testing, or that low potassium always means kidney failure. In reality, multiple tests and risk factors guide accurate assessment.
Kidney tests are powerful tools for early detection and ongoing management. Keep track of creatinine, eGFR, uACR, and electrolytes, and don’t hesitate to seek a nephrologist’s expertise when thresholds are crossed. Early action can preserve kidney function and improve quality of life.