Which laboratory tests should be ordered to obtain a urine albumin-to-creatinine ratio?

Laboratory Tests Required for Urine Albumin-to-Creatinine Ratio

To obtain a urine albumin-to-creatinine ratio, order a spot urine specimen for simultaneous measurement of urine albumin (in mg/dL) and urine creatinine (in g/dL), which the laboratory will report as mg albumin per gram creatinine. 1

Specific Test Ordering

• Order a "spot urine albumin-to-creatinine ratio" or "urine ACR" as a single test order—most laboratories will automatically measure both albumin and creatinine and calculate the ratio 1
• If your laboratory requires separate orders, request:
  • Urine albumin (measured by immunoassay) 1
  • Urine creatinine (measured by standard creatinine assay) 1
• The laboratory will report the result as mg albumin/g creatinine 1

Optimal Specimen Collection

• Use a first-morning void urine sample whenever possible, as this provides the lowest coefficient of variation (31%) and best correlation with 24-hour albumin excretion 1, 2
• First-morning specimens are particularly important in children and adolescents to avoid false elevations from orthostatic proteinuria 1
• Random spot urine samples are acceptable if first-morning collection is not feasible, though they have slightly higher variability 1, 2

What NOT to Order

• Do not order 24-hour urine collections—they are burdensome, error-prone, and add no additional accuracy compared to spot urine ACR 1, 2
• Do not order timed urine collections for routine screening or monitoring 1
• Avoid measuring urine albumin alone without creatinine, as this is susceptible to false results due to variations in urine concentration 2

Pre-Collection Instructions

• Patients should refrain from vigorous exercise for 24 hours before sample collection, as exercise can transiently elevate albumin excretion 1
• Avoid collection during menstruation, active urinary tract infection, fever, marked hyperglycemia, or uncontrolled hypertension, as these conditions can falsely elevate results 1, 2

Result Interpretation Reference Ranges

• Normal (A1): <30 mg/g creatinine 1
• Moderately increased albuminuria (A2): 30-299 mg/g creatinine 1
• Severely increased albuminuria (A3): ≥300 mg/g creatinine 1

Confirmation Testing

• If ACR is ≥30 mg/g, confirm with 2 out of 3 specimens collected over 3-6 months before diagnosing persistent albuminuria 1, 2
• This confirmation step is critical due to high day-to-day biological variability in albumin excretion 1, 2

Common Pitfall to Avoid

The most common error is ordering a "urinalysis with microscopy" or "urine dipstick" expecting to get an albumin-to-creatinine ratio—these tests only provide qualitative protein detection and will not give you the quantitative ACR needed for diagnosis and staging of kidney disease 1. You must specifically order "urine albumin-to-creatinine ratio" or "spot urine ACR" to obtain the correct test.