The Microalbumin Creatinine Ratio (MACR), also known as the Urine Albumin-Creatinine Ratio (UACR), is a screening tool used to detect early signs of kidney damage. Kidneys filter waste from the blood, but when they are impaired, small amounts of the blood protein albumin can leak into the urine. The MACR identifies this leakage long before physical symptoms appear, allowing for intervention at the earliest stage of potential kidney disease.
Understanding the Components of the Ratio
The test measures two substances in a single urine sample: albumin and creatinine. Albumin is the most abundant protein in the blood. Healthy kidneys prevent almost all albumin from passing through their delicate filters, called glomeruli. The presence of even a small amount of albumin in the urine suggests these filters are compromised and leaking.
Creatinine is a waste product generated by muscle tissue breakdown, excreted into the urine at a relatively constant rate. Measuring the ratio of albumin to creatinine improves the test’s accuracy. Urine concentration varies significantly based on hydration, meaning measuring albumin alone can produce misleading results. Comparing albumin to the consistent amount of creatinine normalizes the measurement, correcting for how concentrated or dilute the urine sample is.
Interpreting the Reference Ranges
The interpretation of the Microalbumin Creatinine Ratio depends on specific numerical thresholds used to classify the degree of albumin leakage. Results are typically expressed in milligrams of albumin per gram of creatinine (mg/g) or milligrams per millimole (mg/mmol). A result of less than 30 mg/g (or below 3.0 mg/mmol) is considered within the normal range for adults.
If the ratio falls between 30 and 299 mg/g (or 3 and 30 mg/mmol), the result is classified as moderately increased albuminuria, historically known as microalbuminuria. This finding indicates early, mild damage to the kidney filters and places the individual in a higher-risk category for progressive kidney disease. A ratio of 300 mg/g or greater (more than 30 mg/mmol) is classified as severely increased albuminuria, or macroalbuminuria.
Some guidelines recognize sex-specific differences in the normal range due to variations in muscle mass, which affects creatinine excretion. For instance, a normal range may be defined as less than 17 mg/g for men and less than 25 mg/g for women. While the standard 30 mg/g threshold is widely used for initial screening, providers may consider these sex-specific cutoffs for a more nuanced interpretation.
Conditions Leading to Elevated Results
A persistently elevated Microalbumin Creatinine Ratio is most often linked to chronic conditions that damage the body’s vascular system, particularly Type 1 and Type 2 Diabetes and Hypertension (high blood pressure). In diabetic patients, chronically high blood sugar levels injure the tiny blood vessels within the glomeruli, causing the filtering unit to become abnormally permeable. This damage compromises the glomerular filtration barrier, leading to albumin leakage into the urine.
High blood pressure similarly stresses the delicate renal arteries and capillaries, contributing to structural changes and inflammation within the kidney’s filtering units. The resulting albuminuria is not just a sign of local kidney damage. It is also a strong marker of widespread endothelial dysfunction, indicating a broader issue with the lining of blood vessels throughout the body. The combination of diabetes and hypertension significantly accelerates the rate of kidney function decline.
The MACR can also be temporarily elevated by several transient, non-disease-related factors. A result may be falsely high if the sample was collected shortly after intense physical exercise, which temporarily increases albumin excretion. Acute health events, such as a fever, a urinary tract infection, or acute inflammation, can also cause a temporary spike in the ratio. Therefore, a single high reading is rarely used to diagnose chronic kidney damage.
Confirmatory Testing and Management
Because the MACR can be influenced by temporary factors, an initial abnormal result requires further follow-up to confirm a diagnosis of chronic kidney disease. Healthcare providers typically request that the test be repeated two more times over a period of three to six months. A diagnosis of persistent albuminuria is only confirmed if at least two out of the three collected samples show an elevated ratio.
Confirmation of a persistently high ratio prompts management strategies focused on protecting the kidneys and slowing damage progression. Treatment involves controlling underlying chronic conditions, including maintaining optimal blood sugar levels for individuals with diabetes and managing blood pressure for those with hypertension. Specific medications are prescribed to protect the kidneys by reducing pressure within the glomeruli. These primarily include Angiotensin-Converting Enzyme (ACE) inhibitors or Angiotensin II Receptor Blockers (ARBs), which reduce albumin excretion and preserve kidney function.