Quality assurance of white blood cell labeling with a test based on adherence

A new quality control assay was developed based on the premise that proper radioactive labeling should not affect the adherence characteristics of white blood cells to nylon fibers. Heparinized whole blood with trace amounts of radioactively labeled white blood cells was passed over nylon fiber columns and eluted in eight fractions. Percent radioactive adherence (%RA) and percent white blood cell adherence (%WBCA) were determined for each fraction. Regression lines (%RA versus %WBCA) were calculated for 9 samples labeled properly with 111In-oxine and for 17 samples intentionally subjected to improper labeling. Properly labeled preparations had a median slope = 1.05 and an intercept = 1%. Improperly labeled preparations had significantly lower slopes and/or higher intercepts. By the use of +/- 2 s.d. ranges as indicators of proper labeling (slope of 0.71-1.74; intercept of -35%-37%), the test had 100% sensitivity and 94% specificity. We conclude that proper labeling with 111In-oxine preserves the adherence characteristics of white blood cells, that improper labeling may affect the binding strength of white blood cells (decrease in slope) and/or lead to formation of sticky cell subgroups (increased intercept) and that the quality control assay can objectively assess the impact of labeling on adherence.