Laboratory Markers for Diagnosing Kidney Disease
To definitively diagnose kidney disease in a patient with diabetes or hypertension, measure serum creatinine with eGFR calculation using the 2009 CKD-EPI equation and obtain a spot urine albumin-to-creatinine ratio (ACR) from a first morning sample—these two tests together identify both reduced kidney function and glomerular damage, the hallmarks of chronic kidney disease. 1, 2
Core Diagnostic Tests
Serum Creatinine and eGFR
- Calculate eGFR using the 2009 CKD-EPI equation rather than relying on serum creatinine alone, as creatinine can remain in the normal range despite significant kidney function loss 1, 2, 3
- eGFR <60 mL/min/1.73 m² sustained for >3 months defines CKD, regardless of other findings 1, 4
- The CKD-EPI equation requires only age, sex, race, and serum creatinine, making it practical for routine use 1, 3
Albuminuria Assessment
- Obtain spot urine ACR from a first morning void to detect kidney damage, as this is more sensitive than dipstick testing and avoids the inaccuracy of 24-hour collections 1
- ACR ≥30 mg/g indicates abnormal albuminuria and confirms kidney damage even when eGFR is normal 1
- Confirm persistent albuminuria by repeating the test—2 of 3 positive samples over 3 months establishes chronicity in diabetic patients 1
Critical distinction: Microalbuminuria (30-300 mg/g) represents early, potentially reversible kidney damage, while macroalbuminuria (>300 mg/g) indicates established disease 1
Staging and Risk Stratification
Once CKD is confirmed, stage the disease using both eGFR and albuminuria categories together, as this combined approach predicts progression risk and mortality better than either marker alone 1:
- Stage 3a (eGFR 45-59) with ACR <30 mg/g = moderate risk
- Stage 3b (eGFR 30-44) with any albuminuria = high risk
- Stage 4 (eGFR 15-29) = very high risk, requires nephrology referral 1, 2
Additional Essential Tests
Electrolytes and Metabolic Panel
- Measure serum potassium, sodium, bicarbonate, calcium, and phosphorus to identify CKD complications like hyperkalemia, metabolic acidosis, and mineral bone disorder 2, 4
- Blood urea nitrogen (BUN) helps differentiate prerenal azotemia from intrinsic kidney disease when the BUN-to-creatinine ratio is calculated 2
Urinalysis with Microscopy
- Examine urine sediment for dysmorphic red blood cells, red cell casts, and white blood cells to distinguish glomerular disease from other causes 1, 5
- Active sediment with RBC casts suggests glomerulonephritis requiring urgent nephrology referral 6
Screening Frequency
Screen annually in patients with diabetes, hypertension, age >60 years, family history of CKD, or cardiovascular disease 1, 5
Recheck within 1-2 weeks after starting or adjusting ACE inhibitors, ARBs, or diuretics to detect acute changes in creatinine or potassium 2
Monitor every 3-6 months once CKD stage 3 is established, increasing to every 1-3 months for stage 4-5 disease 2
When to Suspect Non-Diabetic Kidney Disease
Even in diabetic patients, refer to nephrology immediately if any of these atypical features are present 1, 7:
- Absence of diabetic retinopathy with significant proteinuria
- Rapid eGFR decline (>5 mL/min/1.73 m² per year)
- Active urinary sediment with RBC casts
- Diabetes duration <10 years with advanced kidney disease
- Nephrotic-range proteinuria (ACR >3500 mg/g) without retinopathy
Common Pitfalls to Avoid
Do not rely on serum creatinine alone—it underestimates kidney dysfunction, particularly in elderly patients with reduced muscle mass 1, 5
Avoid testing during acute illness—vigorous exercise, fever, heart failure exacerbation, or uncontrolled hyperglycemia cause transient proteinuria elevation 1, 6
Do not use 24-hour urine collections routinely—spot ACR is equally accurate and far more practical for screening and monitoring 1, 6
Confirm abnormal results before labeling a patient with CKD—single elevated values may be transient 1