How to Order a Urine Albumin-to-Creatinine Ratio (UACR)
Specimen Collection Method
Order a first-morning void spot urine sample for UACR measurement—this is the preferred collection method because it provides the lowest coefficient of variation (31%) and best reproducibility compared to random samples or 24-hour collections. 1
- If a first-morning void is not practical (e.g., in outpatient clinic settings), a random spot urine sample is acceptable, though it will have slightly higher variability. 1, 2
- Never order a 24-hour urine collection—spot UACR is more convenient, equally accurate, and eliminates the errors inherent in timed collections. 1
Specific Ordering Instructions
- Order as: "Urine albumin-to-creatinine ratio" or "UACR" on a spot (untimed) urine sample 1
- The laboratory will measure both urinary albumin (mg/L) and urinary creatinine (mg/dL or g/L) from the same sample and report the ratio in mg/g 1
- Ensure the laboratory's lower limit of quantitation for albumin is ≤3 mg/L to maximize diagnostic utility, particularly for detecting low-level albuminuria with prognostic significance 3
Timing and Patient Preparation
- Collect at the same time of day for serial monitoring to minimize variability 1
- The patient should not have eaten for at least 2 hours prior to collection 1
- Avoid collection during or within 24 hours of:
Confirmation Strategy
Because UACR has high day-to-day variability (coefficient of variation ~49%), you must confirm any elevated result (≥30 mg/g) with 2 additional first-morning samples over the subsequent 3–6 months before diagnosing persistent albuminuria. 1, 4
- If 2 out of 3 samples show ACR ≥30 mg/g, the diagnosis of persistent albuminuria is confirmed 1
- A single elevated UACR has only a 50% probability of representing a true ≥30% change; obtaining 2 collections at each time point increases this probability to 97% 4
Screening Frequency by Population
| Patient Population | When to Begin Screening | Frequency |
|---|---|---|
| Type 1 diabetes | 5 years after diagnosis [1] | Annually [1] |
| Type 2 diabetes | At time of diagnosis [1] | Annually [1] |
| Hypertension or other CKD risk factors | At diagnosis [2] | Every 1–2 years [2] |
| eGFR <60 mL/min/1.73 m² or ACR ≥30 mg/g | Already established | Every 6 months [1] |
Result Interpretation Categories
- Normal: <30 mg/g creatinine 1
- Moderately increased albuminuria (A2): 30–299 mg/g creatinine 1
- Severely increased albuminuria (A3): ≥300 mg/g creatinine 1
Common Pitfalls to Avoid
- Do not order "urine protein" or "urine dipstick protein" instead of UACR for diabetic patients—albumin is the preferred and more sensitive marker 5
- Do not rely on urine albumin alone without simultaneous creatinine measurement, as this is susceptible to false results from variations in urine concentration 1
- Do not assume a single normal UACR excludes future risk—UACR is a continuous variable, and even values within the normal range (<30 mg/g) carry prognostic information for cardiovascular and renal outcomes 1
- Do not forget to order serum creatinine and calculate eGFR simultaneously—30–50% of diabetic CKD cases present with reduced eGFR without albuminuria 6