Peripheral blood monocyte counting: towards a new reference method

Area of Science:

• Hematology
• Immunology
• Clinical Chemistry

Background:

• Monocyte counting is crucial for diagnosing and monitoring various medical conditions.
• Traditional manual differential counts can be labor-intensive and prone to variability.
• Flow cytometry using fluorescence-labeled monoclonal antibodies is emerging as a potential reference method.

Purpose of the Study:

• To compare the precision and accuracy of monocyte counting using automated hematology analyzers and flow cytometry against manual differentials.
• To evaluate flow cytometry as a potential reference method for monocyte enumeration.

Main Methods:

• Compared monocyte counts from Coulter STKS, Cobas Argos 5 Diff, manual differential, and Coulter Epics Profile II flow cytometer.
• Utilized double-staining with CD45-FITC and CD14-PE fluorescence-labeled monoclonal antibodies for flow cytometry.
• Assessed precision and accuracy using normal and abnormal samples, and analyzed sex-based differences in monocyte counts.

Main Results:

• Automated methods (STKS, Argos, Profile II) demonstrated superior precision compared to manual differentials.
• Good correlation was observed between automated methods and manual counts (STKS: r=0.934, Argos: r=0.808, Profile II: r=0.924).
• Flow cytometry (Profile II) showed minimal bias and identified higher monocyte counts and wider normal ranges in males compared to females.

Conclusions:

• Flow cytometry provides an efficient and accurate tool for evaluating monocyte counting performance of hematology analyzers.
• Flow cytometry is a suitable successor to the manual differential for establishing a reference method for monocyte counting.
• Sex-specific reference ranges for monocyte counts should be considered.