How to quantify urinary microalbumin (Microalbuminuria) results?

From the Guidelines

Urine microalbumin results should be quantified using the albumin-to-creatinine ratio (ACR) in a random spot collection, with normal values being less than 30 mg/g, microalbuminuria between 30-300 mg/g, and macroalbuminuria above 300 mg/g, as recommended by the most recent guidelines 1. To quantify microalbumin, collect a random urine sample and measure both albumin and creatinine levels. The ACR is calculated by dividing the albumin concentration (mg) by the creatinine concentration (g), resulting in a value expressed as mg/g.

Methods of Quantification

• Measurement of the albumin-to-creatinine ratio in a random spot collection (preferred method)
• 24-h collection with creatinine, allowing the simultaneous measurement of creatinine clearance
• Timed (e.g., 4-h or overnight) collection

Interpretation of Results

• Normal ACR values are less than 30 mg/g
• Values between 30-300 mg/g indicate microalbuminuria
• Values above 300 mg/g represent macroalbuminuria or clinical proteinuria Quantifying microalbumin is essential for early detection of kidney damage, particularly in patients with diabetes or hypertension, as it can appear years before clinical proteinuria develops. Regular monitoring allows for timely intervention to slow progression of kidney disease, as supported by previous studies 1.

Key Considerations

• At least two of three specimens collected within a 3- to 6-month period should be abnormal before considering a patient to have crossed one of these diagnostic thresholds
• Exercise within 24 h, infection, fever, congestive heart failure, marked hyperglycemia, marked hypertension, pyuria, and hematuria may elevate urinary albumin excretion over baseline values
• Annual measurement of albuminuria is useful to assess risk and treatment, with a goal of reducing albuminuria by at least 30% to 50% and ideally achieving a uACR of <30 mg/g 1.

From the Research

Quantification of Urine Microalbumin Results

To quantify urine microalbumin results, several methods can be used, including:

• Measurement of albumin excretion rate (AER) in a timed urine sample, which is considered the gold standard for defining microalbuminuria 2
• Albumin-to-creatinine ratio (ACR) in a random or first morning urine sample, which is a widely used method for screening and monitoring kidney damage 3, 4, 2, 5
• Immunoturbidimetric assays for urinary albumin quantification and enzymatic assays for urinary creatinine quantification, which can be used to assess ACR 5

Factors Affecting Quantification

Several factors can affect the quantification of urine microalbumin results, including:

• Patient preparation and time of day of sample collection, which can affect ACR results 4
• Intermethod differences in urinary albumin and creatinine measurement, which can affect ACR results 4, 5
• Reference intervals for ACR, which do not take into account intergroup differences in creatinine excretion and the continuous increase in risk related to albumin excretion 4

Clinical Significance

The clinical significance of quantifying urine microalbumin results lies in its ability to:

• Identify patients with kidney damage and predict progression of kidney disease and cardiovascular disease 3, 4, 6
• Monitor the impact of antihypertensive therapy and other treatments on kidney function 3
• Guide treatment decisions, such as the use of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers, which can reduce the risk of end-stage renal disease and doubling of serum creatinine levels in patients with diabetes and albuminuria 6