MSFinals-2883
A 32-year-old smoker presents with acute shortness of breath and oxygen saturation of 84% on air. He has been feeling unwell and fatigued for a week, with worsening shortness of breath over the past 24 hours and two episodes of haemoptysis. On examination, he has sinus tachycardia, a blood pressure of 140/85 mmHg, normal JVP, and widespread coarse crackles on chest auscultation. Blood tests reveal a haemoglobin level of 92 g/L (130-180), urea level of 40 mmol/L (2.5-7.5), and creatinine level of 435 μmol/L (60-110). The urine dipstick shows +++ blood and ++ protein. A chest radiograph shows widespread patchy opacification. What is the most likely cause of his presentation?