Hematology 1 Practice Test 2026 - Free Hematology Practice Questions and Study Guide

Counting red cells with a hemocytometer relies on a diluting fluid that keeps cells evenly dispersed and preserves their integrity for accurate counting. Dacie's fluid, known as Formol-Citrate, fixes the erythrocytes with formaldehyde and provides citrate to prevent coagulation, creating a stable, well-dispersed suspension. This reduces cell clumping and morphological changes, making RBC counts more reliable and reproducible. In contrast, plain diluents like normal saline or Ringer's solution do not fix cells, so RBCs can crenate, swell, or aggregate, leading to inconsistent counts. Giemsa stain is a staining reagent for slides, not a diluting fluid for counting cells. Hence, Dacie's fluid (Formol-Citrate) is the best choice for RBC dilution.