A 52-year-old woman presents with acute pleuritic chest pain and dyspnoea. She has a recent long-haul flight and a history of oestrogen therapy. Her vital signs: BP 128/74 mmHg, HR 104 beats/min, RR 22, SpO₂ 94% on room air, no leg swelling. According to the Wells score for pulmonary embolism, which of the following most influences whether to pursue D-dimer testing versus immediate imaging?