A 65 year old man presented to the emergency department with a 10 day history of dark urine, general malaise, and progressive shortness of breath. He had a history of rheumatic heart disease and had been on warfarin since he had a metallic mitral valve replacement in 1984. He was a retired teacher, drank a minimal amount of alcohol, and was a non-smoker. He had no family history of cancer. On examination he was jaundiced with a sinus tachycardia (120 beats/min) and a pansystolic murmur. His other vital signs were normal. On examination, his other systems were normal except for mild suprapubic tenderness, as were the results of a digital rectal examination. His urine was rust coloured (fig 1⇓) with no blood clots. Urine dipstick was positive for blood (3+), protein (3+), and leucocytes (3+), but negative for nitrites. No red blood cells or casts were noted during microscopy. Fig 1 Patient’s urine on admission The table⇓ shows the results of his initial laboratory investigations. A peripheral blood film showed red cell fragments, polychromasia, and normal platelets (a representative smear is shown in fig 2⇓). The results of chest radiography, computed tomography of the kidneys, and ultrasound of the urinary tract were also unremarkable. Serial sepsis screens and three sets of blood cultures for endocarditis were all negative. View this table: Laboratory test results on admission Fig 2 A representative blood film showing red cell fragments (arrows) ### 1. What are the causes of dark urine? #### Answer Haematuria, menstrual contamination, haemoglobinuria, and myoglobinuria will cause dark urine that is positive for blood on urine dipstick testing. Red cells …