Nephrons are the functional units of the kidney, with each kidney having about one million nephrons. Nephron functions consist of two major components. First, glomerular capillaries are the site of glomerular filtration, movement of water and small solutes (electrolytes, glucose, amino acids, urea, creatinine, and numerous other biomolecules and wastes) from the plasma to Bowman’s space. Second, the nephron tubule that receives the fluid entering Bowman’s space conducts reabsorption from and secretion into the filtered fluid, progressively retaining needed water and solutes while concentrating wastes for excretion in the urine. Measurements of albumin excretion sometimes use timed urine collections, with albumin excretion expressed as mg/minute, mg/hour, or mg/24 hours. An alternative is to assay a single, early morning spot urine sample, followed by dividing the albumin concentration by the creatinine concentration (albumin/creatinine ratio). Urine albumin measurements are made quantitatively by immunoassay and are specific to albumin.