Normal individuals excrete very small amounts of protein in the urine. Albumin is the most common type of protein in the blood and the urine. All patients with chronic kidney disease (CKD) should be screened for albuminuria. Persistent increased protein in the urine is one of the principal markers of kidney damage, acting as an early and sensitive marker in many types of kidney disease.
The Albumin Creatinine Ratio is calculated as follows:
Albumin (mg/L) X 100 = Albumin (mg)/Creatinine (g)
A routine dipstick is not sensitive enough to detect small amounts of urinary protein. Therefore, it is recommended that screening in adults at risk for cardiovascular disease (CVD) and CKD be done by testing for albuminuria. According to the American Kidney Foundation the urinary albumin-to-creatinine ratio (ACR) is the method of choice to detect elevated urinary protein. The recommended method to evaluate albuminuria is to measure urinary ACR in a spot urine sample. ACR is calculated by dividing albumin concentration in milligrams by creatinine concentration in grams. Although the 24-hour collection has been the “gold standard,” alternative methods for detecting protein excretion such as urinary albumin-to-creatinine ratio (ACR) correct for variations in urinary concentration due to hydration, as well as provide more convenience than timed urine collections. The spot urine specimen has been shown to correlate well with 24-hour collections.
Moderately increased albuminuria, historically known as microalbuminuria, (ACR 30-300 mg/g) refers to albumin excretion above the normal range, but below the level of detection by tests for total protein. Severely increased albuminuria, historically known as macroalbuminuria, (ACR >300) refers to a higher elevation of albumin associated with progressive decline in estimated glomerular filtration rate (eGFR).