A 61-year-old male presents with anorexia, nausea, dizziness, fatigue, and generalized jaundice for 1 month. Laboratory tests: Hb 80g/L, reticulocyte count 0.20 (20%), peripheral smear shows spherocytes 0.06 (6%), slightly increased RBC osmotic fragility, urine bilirubin (-), urine urobilinogen strongly positive, urine occult blood (-), serum total bilirubin (TBil) 76.15 μmol/L, direct bilirubin 6.84 μmol/L, ALT <40 U/L. A diagnosis of hemolytic anemia is suspected. Which of the following laboratory tests should be performed first to determine the etiology of hemolysis?