The determination of the difference between a measured urine osmolarity and a calculated urine osmolarity is a valuable diagnostic tool. This difference, often termed the urine osmolar gap, can provide insight into the presence of unmeasured osmoles in the urine. The calculated osmolarity is typically derived from the major measured solutes in urine, such as sodium, potassium, urea, and glucose. For example, a calculation might involve the formula: 2 x (Urine Sodium + Urine Potassium) + (Urine Urea / 2.8) + (Urine Glucose / 18), where the concentrations are in mEq/L or mg/dL, respectively.
Assessing this differential is important in evaluating patients with suspected electrolyte imbalances, renal dysfunction, or exposure to certain toxins. A significantly elevated value suggests the presence of substances not routinely accounted for in the standard calculation, potentially indicating the excretion of unusual osmotically active compounds. Historically, this assessment was performed manually. The advent of readily available tools to automate this calculation improves efficiency and reduces the possibility of errors associated with manual computation.
