Is a Urine Albumin-to-Creatinine Ratio (UACR) test the same as a microalbumin test?

UACR and Microalbumin Testing: Understanding the Relationship

UACR (Urine Albumin-to-Creatinine Ratio) and microalbumin testing measure the same substance—urinary albumin—but UACR is the preferred standardized method that expresses albumin relative to creatinine concentration, while "microalbumin" is an outdated term referring to albumin measurements in a specific range. 1

Key Distinctions

What UACR Measures

• UACR is a ratio that divides urinary albumin concentration by urinary creatinine concentration, typically expressed as mg albumin per g creatinine 1
• This ratio corrects for urine concentration variability caused by hydration status, making it more reliable than measuring albumin alone 1
• Normal UACR is defined as <30 mg/g creatinine 1

The "Microalbumin" Terminology Issue

• The term "microalbuminuria" is no longer recommended by the American Diabetes Association as of 2015 1
• Historically, "microalbuminuria" referred to UACR values between 30-299 mg/g, while "macroalbuminuria" meant >300 mg/g 1
• Current guidelines simply refer to "increased urinary albumin excretion" (≥30 mg/g) because albuminuria exists on a continuum rather than discrete categories 1

Clinical Testing Approach

Why UACR is Superior to Albumin Alone

• Measuring albumin concentration alone (whether by immunoassay or dipstick) without simultaneous creatinine measurement is susceptible to false-negative and false-positive results due to hydration-related concentration variations 1
• UACR from a random spot urine collection is the recommended screening method—timed or 24-hour collections add burden without improving accuracy 1

Important Testing Considerations

• Two of three specimens collected within 3-6 months should be abnormal before confirming albuminuria due to biological variability 1
• Transient elevations can occur with exercise within 24 hours, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, or marked hypertension 1

Practical Clinical Implications

When a laboratory reports "microalbumin," they are typically measuring urinary albumin concentration and may or may not be calculating the UACR. Always request or calculate the UACR yourself to ensure proper interpretation, as the ratio provides superior diagnostic accuracy compared to albumin concentration alone 1.

The shift away from "microalbuminuria" terminology reflects recognition that even values within the previously "normal" range (<30 mg/g) carry prognostic significance for cardiovascular and renal outcomes, and the risk increases continuously across the spectrum 1.