The Urine Albumin-to-Creatinine Ratio (UACR) is a simple calculation used as a key indicator of kidney health. Derived from a single urine sample, it provides a standardized measure of albumin excretion. The UACR screens for albuminuria, a condition where an abnormally high amount of albumin is present in the urine. Detecting this is important because it often signals damage to the kidney’s filtering units (glomeruli). An elevated UACR can signal the onset of chronic kidney disease, especially in individuals with diabetes or high blood pressure.
Required Measurements for UACR
Calculating the UACR requires the measurement of two components from a urine sample: albumin and creatinine. Albumin is a major blood protein that the kidneys normally retain. Its presence in the urine (albuminuria) indicates that the kidney’s filtering membrane has been compromised, allowing the protein to leak through.
Creatinine is a waste product of muscle breakdown that is filtered and excreted into the urine at a steady rate. The concentration of creatinine standardizes the albumin measurement. Since urine concentration fluctuates based on hydration, dividing albumin by creatinine corrects for these variations. This correction allows a random “spot” urine sample result to approximate the total albumin excretion over 24 hours.
Laboratories typically measure albumin and creatinine concentrations in milligrams per deciliter (mg/dL). Sometimes creatinine is measured in grams per deciliter (g/dL). The use of different units necessitates a specific mathematical adjustment during the calculation. This ensures the final ratio is expressed in the standardized unit of milligrams of albumin per gram of creatinine (mg/g).
The Step-by-Step Calculation Formula
The UACR is the ratio of urinary albumin concentration to urinary creatinine concentration. The standardized formula yielding the result in mg/g is UACR = Albumin Concentration (mg/dL) / Creatinine Concentration (g/dL). If creatinine is reported in milligrams (mg), it must be converted to grams (g). This conversion is achieved by incorporating a factor of 1000 into the calculation, since one gram equals 1000 milligrams.
When both laboratory values are reported in mg/dL, the calculation uses the expression: UACR (mg/g) = [Albumin (mg/dL) / Creatinine (mg/dL)] x 1000. Multiplying by 1000 converts the ratio into the desired mg/g unit, making the result clinically interpretable. For example, consider a report showing an albumin concentration of 15 mg/dL and a creatinine concentration of 150 mg/dL.
To calculate, first divide 15 mg/dL of albumin by 150 mg/dL of creatinine, yielding a raw ratio of 0.1. This raw ratio is then multiplied by the conversion factor of 1000. The final calculated UACR is 0.1 x 1000, which equals 100 mg/g.
Interpreting the UACR Results
After calculation, the UACR (mg/g) is classified into clinical categories indicating the degree of albuminuria. These categories reflect kidney health and the risk for progressive kidney disease. A UACR less than 30 mg/g is considered normal, suggesting kidney filters are working properly and retaining albumin.
A UACR between 30 mg/g and 300 mg/g is classified as moderately increased albuminuria (formerly microalbuminuria). This range suggests early damage to the kidney’s filtering apparatus. Individuals in this range have an increased risk of advanced kidney failure and cardiovascular events, such as heart attack or stroke. If this result persists upon repeat testing over three to six months, it often signifies chronic kidney disease.
Severely increased albuminuria occurs when the UACR is greater than 300 mg/g (formerly macroalbuminuria). This finding indicates extensive damage to the kidney filters. It is associated with a higher likelihood of progressive loss of kidney function, kidney failure, and elevated mortality risk.