Albumin, with a molecular weight of approximately 66.5 kDa, is the most abundant protein in blood plasma, typically present at concentrations of 35-50 g/L. It plays a vital role in maintaining blood oncotic pressure and acts as a carrier for various substances like hormones, fatty acids, and drugs. In a healthy individual, albumin is minimally present in urine, generally less than 30 mg/day, as kidneys retain it during filtration.
Albumin in urine
Elevated levels of albumin in urine, termed albuminuria, indicate potential kidney damage or dysfunction, especially in conditions like diabetes and hypertension. Healthy kidneys retain most albumin, so when glomeruli—the kidney’s filtration units—are damaged, they may leak albumin into the urine. Mild elevation (microalbuminuria, 30–300 mg/day) can signal early kidney impairment, while higher levels (macroalbuminuria, >300 mg/day) often indicate more severe damage. Persistent albuminuria is a marker for chronic kidney disease (CKD) and can also suggest increased cardiovascular risk. Regular monitoring through urine tests helps in early intervention, and lifestyle or medical adjustments can help manage and reduce progression risks.
Detection techniques for albumin in urine
Several techniques are used to measure albumin in urine, each offering distinct advantages:
Dipstick Assay: A quick, semi-quantitative method that uses color changes on a reagent strip to indicate albumin levels, commonly used for initial screening.
Immunoassays: These include Enzyme-Linked Immunosorbent Assay (ELISA) and immunoturbidimetric assays, which rely on antibodies specific to albumin, offering high sensitivity and accuracy for both clinical and research applications.
Urine Albumin-to-Creatinine Ratio (UACR): Commonly used to account for urine concentration variability, comparing albumin levels to creatinine concentration in a single urine sample.
HPLC-UV (High-Performance Liquid Chromatography with Ultraviolet Detection): HPLC-UV offers precise quantification of albumin in urine by separating proteins and detecting albumin based on its absorbance. It’s highly accurate for low-concentration samples and useful in research settings, providing a robust alternative to immunoassays.