Which principle counts RBCs and WBCs?

MLT MCQ #075 — Hematology | CBC Analyzer Question The classical principle used by automated CBC analyzers for counting RBCs and WBCs is A. Colorimetric principle B. Electrical impedance principle C. Flame photometry D. Immunofluorescence 🧠 Think before checking the answer ✅ Correct Answer: B. Electrical Impedance Principle 📝 1-Line Concept In the Coulter principle, blood cells passing through a small aperture cause changes in electrical resistance, producing pulses that are counted as cells. 🔥 DHA / SLE Exam Tip Coulter principle = Electrical impedance = Cell counting RBC/WBC → Impedance Hemoglobin → Colorimetry WBC differential → Light scatter / flow cytometry