Differential Leukocyte Count and Osmotic Fragility Testing

This set explores the vocabulary and methodologies associated with Differential Leukocyte Counts, abnormal cell morphology, WBC shifting theories (Schilling/Arneth), and the various manual and automated methods for assessing Osmotic and Mechanical Fragility of red blood cells.

Differential Leukocyte Count

The enumeration of relative proportions (represented as a percentage) of various white blood cell types observed in a stained blood film.

Wright stain

The commonly used reagent/stain for staining blood cells during a manual differential leukocyte count.

Relative proportions

A measurement where the percentage reported depends on the presence of other cells.

Zigzag method

A scanning technique used during cell counting on a blood smear to decrease errors.

Fibrin threads

Indicators that a blood specimen is about to coagulate; these are checked at the feather edge of the smear.

Corrected WBC count

A calculation performed when more than 5 nucleated red blood cells ($NRBCs$) per 100 leukocytes are found to prevent false high results.

NRBCs (Nucleated Red Blood Cells)

Cells that erroneously elevate automated/manual WBC counts because they are as large as small lymphocytes; they are reported as number per 100 leukocytes.

Toxic granulation

An abnormal leukocyte morphology in neutrophils that serves as an indication of infection or chemical toxicity.

Dohle bodies

Polymorphonuclear ($PMN$) inclusions that are associated with severe bacterial infections.

PMN (Normal Value)

$$57-65\%$$

Lymphocytes (Normal Value)

$$25-35\%$$

Monocytes (Normal Value)

$$4-8\%$$

Eosinophils (Normal Value)

$$2-5\%$$

Basophils (Normal Value)

$$0-1\%$$

Absolute Values

Calculated by multiplying the total list WBC count by the relative value (percentage) of a specific WBC type.

Schilling Count

A systematic method of counting granulocytic cells in groups according to their sequential development stage.

Shift to the Left

An increase in younger granulocytic cells, such as stabs or bands.

Shift to the Right

An increase in older, more mature granulocytic cells.

Regenerative Shift

An increase in the total white blood cell count beyond the normal limit.

Degenerative Shift

A decrease in the total white blood cell count beyond the normal limit.

Arneth Count

A qualitative and quantitative classification of neutrophils based on the number of nuclear lobes they possess.

Osmotic Fragility Test (OFT)

A test for the resistance of red blood cells to hypotonic solutions, which depends on the surface area-to-volume ratio of the cells.

Isotonic solution

A solution with equal osmolarity to the compared environment.

Sanford Method

A standard method for OFT using 2 series of 12 small test tubes and $0.5\%$ NSS; initial and complete hemolysis are recorded by multiplying the tube number by $0.02$.

Dacie Method

The method of choice for OFT using a series of 12 tubes with NSS concentrations ranging from $0.85\%$ to $0.1\%$, measured spectrophotometrically at $540\,nm$.

Mechanical Fragility Test

A test for the resistance of RBCs to trauma, simulating the mechanical stresses cells are subjected to in circulation.

Autohemolysis

The process where various degrees of lysis take place when sterile defibrinated blood is incubated at $37^\circ C$.

Fragiligraph

An automated instrument with a double membrane cuvette used for performing erythrocyte fragility measurements and recording a fragility curve.