Microalbumin/Creatinine Ratio and Albumin/Creatinine Ratio Are the Same Test
Yes, the microalbumin/creatinine ratio is the same test as the albumin/creatinine ratio (ACR). 1 Both terms refer to the same measurement that quantifies the amount of albumin excreted in the urine relative to creatinine.
Terminology Explanation
- The term "microalbumin" is somewhat misleading as it does not refer to a different type of albumin molecule but rather to the detection of albumin in small amounts (below the threshold of standard dipstick tests).
- The American Diabetes Association and other organizations have been moving away from using the term "microalbuminuria" in favor of simply describing the albumin-to-creatinine ratio values 2, 1.
- The KDOQI guidelines specifically endorse "the elimination of 'microalbuminuria' and 'macroalbuminuria' from the diagnostic testing lexicon" 2.
Classification of Albumin Excretion
According to clinical guidelines, urinary albumin excretion is categorized as follows:
| Category | ACR (mg/g creatinine) | 24-h collection (mg/24h) | Timed collection (μg/min) |
|---|---|---|---|
| Normal | <30 | <30 | <20 |
| Microalbuminuria | 30-299 | 30-299 | 20-199 |
| Macroalbuminuria/Clinical albuminuria | ≥300 | ≥300 | ≥200 |
Testing Methods
- The albumin-to-creatinine ratio in a random spot urine collection is the preferred screening method for detecting abnormal levels of albumin in the urine 2.
- First morning void or other morning collections are preferred due to known diurnal variation in albumin excretion 2, 1.
- Standard hospital laboratory assays for urinary protein are not sufficiently sensitive to detect microalbuminuria; specific assays are needed 2.
Clinical Significance
- The presence of elevated albumin in urine (30-299 mg/g creatinine) is an early marker of kidney damage, particularly in patients with diabetes or hypertension 1, 3.
- It is also associated with increased cardiovascular risk 2, 3.
- Due to day-to-day variability in albumin excretion, at least two of three collections over a 3-6 month period should show elevated levels before confirming the diagnosis of microalbuminuria 2, 1.
Common Pitfalls
- Not using specific assays for microalbuminuria detection, as standard dipstick tests only detect albumin levels >300-500 mg/day 1, 3.
- Failing to account for factors that can cause transient elevations in urinary albumin excretion such as short-term hyperglycemia, exercise, urinary tract infections, marked hypertension, heart failure, and acute febrile illness 2.
- Improper storage of urine samples (should be refrigerated if analysis is delayed) 1.
In conclusion, while the terminology may vary, microalbumin/creatinine ratio and albumin/creatinine ratio refer to the same laboratory measurement, which is an important tool for early detection of kidney damage and cardiovascular risk assessment.