hemocytometers

Hemocytometer is a specialized microscope slide used for counting cells in a liquid sample. The counting chamber has a precisely defined depth and a grid etched on the chamber floor to enable cell enumeration using light microscopy. It is commonly used to estimate concentrations of blood cells, such as erythrocytes and leukocytes, as well as cultured cells in research or clinical labs.

Most hemocytometers in use are Neubauer-type counting chambers, or Bürker chambers. They consist of a thick glass slide with a recessed chamber whose depth is fixed (typically 0.1 mm) and a grid pattern that divides the chamber floor into a set of squares for counting. A coverslip is placed over the chamber to form a uniform volume in which cells are counted.

Samples are prepared by diluting the cell suspension with a diluent containing a dye or stain if needed. An appropriately diluted sample is loaded into the chamber and allowed to settle. The operator counts cells within defined squares of the grid, following standard counting rules (e.g., counting certain numbered squares or fields). The concentration is calculated as: cells per milliliter = average cell count per counted square × dilution factor × 10,000. The factor 10,000 accounts for chamber depth and the volume represented by each counted square. For viability testing, trypan blue or similar dyes can be used to distinguish live cells.

Hemocytometry requires careful sample preparation and calibration; manual counting can introduce observer error and clumping or cells adhering to slide may bias results. It remains a simple, inexpensive method and is still used in teaching and in situations where automated counters are not available.