CBC & differential See "How to interpret a CBC with differential" lecture for a detailed discussion. Retic Reticulocytes are immature red blood cells that spend ~3 days maturing in the bone marrow, followed by 1–2 days in the peripheral blood before becoming mature RBCs. Retic count is a real-time indicator of bone marrow erythropoietic activity. Corrected reticulocyte count = % Retic × (Patient's Hct / Normal Hct) Reticulocyte production index (RPI) = Corrected retic count /

Normal ranges varies slightly by labs. WBC Elevated WBC (>11k) Common causes of significant leukocytosis (>15k): Sepsis/ bacterial infection C.difficile C. diff detected in ~25% of patients with WBC >30k without hematologic malignancy Leukocytosis can even precede diarrheal symptoms If no obvious source, test for C. diff even without diarrhea Malignancy (hematologic malignancy, neoplastic syndrome from solid malignancies) Medication (steroid, G-CSF) Physiologic stress (surger