In the OPQRST mnemonic, what does the letter O represent?

• A. Onscene location
• B. Oxygen saturation
• C. Occupation
• D. Onset

Answer: (D)

The letter O in OPQRST stands for onset—the moment when the pain began, including what the patient was doing or what triggered it. Knowing the onset helps gauge urgency and potential causes; for example, sudden pain at rest can signal a life-threatening event like a heart attack, while pain that starts with activity might suggest angina. The other options don’t describe how the pain began: where the event happened, oxygen saturation, or the patient’s occupation are not about the start of the pain. Onset is the correct interpretation because it specifically captures the timing of the pain’s appearance.