Azotemia is an elevation of blood urea nitrogen (BUN) and serum creatinine levels. The reference range for BUN is 8-20 mg/dL, and the normal range for serum creatinine is 0.7-1.4 mg/dL.
Each human kidney contains approximately 1 million functional units known as nephrons, which are primarily involved in urine formation. Urine formation ensures that the body eliminates the final products of metabolic activities and excess water in an attempt to maintain a constant internal environment (homeostasis). Urine formation by each nephron involves 3 main processes, as follows:
• Filtration at the glomerular level
• Selective reabsorption from the filtrate passing along the renal tubules
• Secretion by the cells of the tubules into this filtrate
Perturbation of any of these processes impairs the kidney’s excretory function, resulting in azotemia.
The quantity of glomerular filtrate produced each minute by all nephrons in both kidneys is referred to as the glomerular filtration rate (GFR). On average, the GFR is about 125 mL/min (10% less for women), or 180 L/day. About 99% of the filtrate (178 L/day) is reabsorbed, and the rest (2 L/day) is excreted.