LAUSR

A previously healthy 14-year-old adolescent male of South Asian ancestry presented to the emergency room (ER) with significant fatigue and a 3-month history of abdominal and lower back pain. Two months prior to presentation, he was seen for his abdominal symptoms and diagnosed with constipation by his primary care physician. At the time, he had normal investigations: a normal hemoglobin 129 g/L [normal 125–170 g/L], platelet count 186 × 10/L [150–400 × 10/L], urea 4.9 mmol/L [2.6–7.6 mmol/L], creatinine 56 μmol/L [41–74 μmol/L], and normal findings on abdominal ultrasound. In the ER, he reported no history of bleeding, though there was a note of darker colored stools (one stool per day) for a few days prior to admission. He was noted to be pale by his family and had significant fatigue and decreased oral intake, but no change in urine output, no gross hematuria, swelling, or edema. He had no history of fevers, night sweats, or weight loss. There was a history of cough and congestion a few days prior to presentation. Review of systems was otherwise unremarkable, except for some non-specific arthralgias reported in his back, knees, and neck. Family history was unremarkable from a renal and hematological standpoint, and the parents were not consanguineous. Physical examination revealed a pale adolescent who was afebrile, with a normal heart rate (80 beats/min) and with mildly elevated blood pressure of 129/77 mmHg. Full examination was unremarkable except for a systolic ejection murmur grade II/VI and mild tenderness along the lumbar spine. There was no rash or ecchymoses noted. Musculoskeletal examination did not reveal any joint swelling or erythema. He had normal range of movement of all joints. Investigations revealed a normocytic anemia with hemoglobin 42 g/L [normal 110–145 g/L] and MCV 81.2 fL [76.7– 89.2 fL], white blood cell count 4.53 × 10/L [3.84–9.84 × 10/L], and thrombocytopenia with platelets 19 × 10/L [175–332 × 10/L]. His blood smear showed moderate polychromasia, marked anisocytosis, and severe schistocytes. Coombs/Direct antiglobulin testing was negative. Lactate dehydrogenase was elevated at 2059 U/L [360–730 U/L], with undetectable haptoglobin < 0.08 g/L [0.08–1.79 g/L]. Electrolytes were unremarkable: sodium 136 mmol/L [135– 143 mmol/L], potassium 4.8 mmol/L [3.7–5 mmol/L], chloride 105 mmol/L [99–111 mmol/L], total CO2 21 mmol/L [22–30 mmol/L], ionized calcium mildly low at 1.16 mmol/L [1.22–1.37 mmol/L], magnesium 0.85 mmol/L [0.7–0.95 mmol/L], and phosphate 1.66 mmol/L [1.18– 1.98 mmol/L]. However, there was acute kidney injury with an elevated urea of 12.2 mmol/L [2.8–7.7 mmol/L] and creatinine was 90 μmol/L [40–69 μmol/L]. Urinalysis showed hematuria and proteinuria with urine protein to creatinine ratio of 259.6 mg/mmol [≤ 20 mg/mmol] and albumin to creatinine ratio of 141.9 mg/mmol [< 3.5 mg/mmol]. Given the triad presentation of microangiopathic hemolytic anemia, thrombocytopenia, and impaired renal function, he was diagnosed with a thrombotic microangiopathy (TMA). Further testing for etiology of the TMA was sent. The answers to these questions can be found at https://doi.org/10.1007/ s00467-020-04515-5.