Ammonia is reported in which unit, distinguishing it from other NPN measurements?

• A. ug/dL
• B. mg/dL
• C. mmol/L
• D. ppm

Answer: (A)

Ammonia in blood exists at very low concentrations, so the reporting unit is micrograms per deciliter. This keeps the numbers in a practical, easily read range, unlike other NPN measurements such as urea or creatinine, which are present at higher levels and are therefore reported in mg/dL. Using mg/dL for ammonia would make the values very small and awkward to read, and units like mmol/L or ppm are not the standard clinical reporting conventions for this analyte. In short, the typical clinical practice expresses ammonia in ug/dL to reflect its low concentration with a convenient scale.