A 55 year old man who has been on bed rest for the past 10 days, complain of breathlessness and chest pain. The chest X-ray is normal. The next step in the investigation should be –
**Core Concept**
Deep vein thrombosis (DVT) and pulmonary embolism (PE) are significant concerns in patients who have been immobile for an extended period, such as bed rest. These conditions can cause sudden onset of breathlessness and chest pain due to obstruction of blood flow in the lungs.
**Why the Correct Answer is Right**
In this scenario, the patient's symptoms of breathlessness and chest pain, despite a normal chest X-ray, raise suspicion for pulmonary embolism. A normal chest X-ray does not rule out PE, as many patients with PE may have a normal chest X-ray. The next step in investigation should be a D-dimer test to assess for the presence of fibrin degradation products, which can indicate thrombosis. If the D-dimer is elevated, further imaging with a CT pulmonary angiogram (CTPA) would be warranted to visualize the pulmonary arteries and confirm the presence of a PE.
**Why Each Wrong Option is Incorrect**
**Option A:** An electrocardiogram (ECG) may be useful in evaluating chest pain, but it is not the next step in investigation for suspected PE, especially with a normal chest X-ray.
**Option B:** A complete blood count (CBC) may show signs of infection or inflammation, but it is not specific for diagnosing PE.
**Option C:** A chest X-ray is already normal, making a repeat X-ray unnecessary and not helpful in diagnosing PE.
**Clinical Pearl / High-Yield Fact**
In patients with suspected PE, a normal chest X-ray does not rule out the diagnosis, and further imaging with a D-dimer test or CT pulmonary angiogram is necessary to confirm or exclude the presence of a PE.
**Correct Answer:** D. D-dimer test.