How UACR Testing is Performed
UACR testing is performed by collecting a random spot urine sample—preferably a first morning void—and measuring both albumin and creatinine concentrations in the same sample, then calculating their ratio (albumin in mg divided by creatinine in grams). 1
Sample Collection Method
Collect a random spot urine sample, with first morning void being the preferred specimen because it has the lowest coefficient of variation (31%) and minimizes day-to-day variability 2
The sample should ideally be collected at the same time of day, with the patient having not ingested food for at least 2 hours prior to collection to further reduce variability 2
Timed or 24-hour urine collections are unnecessary—they are more burdensome and add little to prediction or accuracy compared to spot samples 1
Laboratory Analysis
Both albumin and creatinine are measured simultaneously in the same urine sample 1
Albumin is typically measured by immunoassay or spectrophotometric dye-binding methods (such as tetrabromophenol blue) 3
Creatinine is measured using colorimetric methods (such as the Jaffe assay) 3
The ratio is calculated as: UACR (mg/g) = [Urine Albumin (mg/L) ÷ Urine Creatinine (g/L)] 1
Why Creatinine is Measured
Creatinine serves solely as a normalization factor to correct for variations in urine concentration due to hydration status—it is not an independent marker of kidney function in this test 2, 4
Measuring albumin alone without creatinine is less expensive but susceptible to false-negative and false-positive results due to variable urine dilution 1
Point-of-Care Testing Options
Point-of-care (POC) devices are available for UACR testing in settings where laboratory access is limited, such as rural areas or community pharmacies 1
POC devices must demonstrate the ability to produce positive results in 85% of people with significant albuminuria (ACR ≥30 mg/g) and maintain appropriate quality standards 1
Currently, POC testing for UACR is less widely available than laboratory-based testing, with median testing rates around 53% in US healthcare organizations compared to 90% for serum creatinine 1
Confirmation Requirements
Due to high biological variability (>20% between measurements), two out of three specimens collected within a 3-6 month period should show elevated values before confirming persistent albuminuria 1, 2
Use first morning void samples for all confirmatory testing 2
Factors That Can Falsely Elevate Results
Before confirming chronic kidney disease, exclude these transient causes that can temporarily elevate UACR 2:
- Exercise within 24 hours
- Active urinary tract infection or fever
- Menstruation
- Marked hyperglycemia (poorly controlled blood sugar)
- Congestive heart failure exacerbation
- Marked uncontrolled hypertension
Result Interpretation
- Normal: <30 mg/g creatinine 1, 2
- Moderately increased albuminuria: 30-299 mg/g creatinine 1, 2
- Severely increased albuminuria: ≥300 mg/g creatinine 1, 2
Clinical Pitfalls to Avoid
Do not use dipstick tests for albumin alone—they lack the precision needed for accurate CKD screening and staging 1
Do not diagnose albuminuria based on a single elevated measurement—always confirm with repeat testing over 3-6 months 1, 2
Do not order 24-hour urine collections for routine screening—they provide no additional accuracy and reduce patient compliance 1