What is the specimen of choice for analysis of acid-base disturbances involving pulmonary dysfunction in an adult?

• A. Venous blood
• B. Arterial blood
• C. Capillary blood
• D. Urine

Answer: (B)

Arterial blood is the specimen of choice because arterial blood gas analysis provides direct measurements of PaO2, PaCO2, pH, and bicarbonate, which together define both oxygenation and the ventilatory status. When pulmonary dysfunction is involved, you need to know how well the lungs are exchanging gases, and arterial blood reflects this since it represents blood that has just left the lungs. Venous blood would show the mixed venous gas content after tissue metabolism and doesn’t accurately indicate lung gas exchange. Capillary blood can be variable and less reliable for precise PaO2 and PaCO2, while urine cannot reveal current respiratory status or acid-base balance. In adults, arterial sampling (often via arterial puncture or an arterial line) provides the most accurate assessment of acid-base disturbances related to pulmonary function.