The ideal thickness of a peripheral blood film is a single layer of cells with minimal overlap because this allows for clear visualization and accurate morphological assessment of individual blood cells. Overlapping cells or thick areas cause misinterpretation of cell size, shape, and staining characteristics, leading to diagnostic errors. A well-prepared film ensures that each cell is distinct, enabling precise identification of abnormalities. This optimal thickness is crucial for reliable hematological evaluation and clinical decision-making.

Reference: Clinical Hematology: Theory and Procedures, Mary Louise Turgeon, 6th Edition.