Which laboratory result provides the most important information about respiratory status in an acute asthma attack?

• A. CBC.
• B. ABG.
• C. BUN.
• D. PTT.

Answer: (B)

Evaluating ventilation and gas exchange is what matters most during an acute asthma attack. An arterial blood gas directly measures how well oxygen is getting into the blood and how effectively carbon dioxide is being removed, along with the acidity (pH) of the blood. In an asthma flare, you want to know PaO2, PaCO2, and pH because they reveal the current state of breathing and whether the patient is compensating or tiring. Early in an attack, you may see low CO2 due to hyperventilation, and a high pH, but as fatigue progresses CO2 can rise, leading to respiratory acidosis. These changes are crucial for guiding treatment decisions, including escalation of therapy or need for ventilatory support. The other tests don’t assess gas exchange or ventilation directly: a CBC looks at blood cells and infection or inflammation, BUN reflects kidney function, and PTT relates to coagulation. So the arterial blood gas provides the most immediate and comprehensive view of respiratory status in this situation.