Stability of complete blood count and microscopic differential count parameters

Overview

Introduction:
Complete blood count (CBC) including the automated differential white blood cell count (WBC differential) represent a routine laboratory test. The time interval between sample collection and testing (sample stability) may have an important effect on the quality of test results. The aim of this study was to analyse changes in CBC (including new advanced parameters) and WBC differential performed both by a haematology analyser and microscopic examination at different storage temperatures over time, including qualitative morphological changes.

Materials and methods:
Data were obtained from 20 healthy volunteers (6 males/14 females) from whom 3 tubes with K3EDTA venous blood were taken. Blood samples were measured using the XE2100 haematology analyser (TOA Sysmex). Peripheral blood smears were performed on the SP1000i automatic analyser (TOA Sysmex). After collection, samples were repeatedly measured at predetermined time intervals of 20 minutes to 72 hours and stored at room temperature (18°C to 25°C) or refrigerated (2°C to 8°C).

Results:
Statistically significant changes were observed both in the directly measured parameters (HCT and PCT) and in derived parameters (MCV, MCHC, RDW, PDW, MPV, P-LCR) after 12 hours of storage at room temperature. All observed parameters are given in Table 1. RET-He and IPF parameters also changed significantly over time. In contrast, no significant changes were observed in the remaining CBC parameters. Automated WBC differentials were stable for the duration of the study (72 hours), with the exception of monocyte level count (both absolute and relative), which was stable only at lower storage temperature (2°C to 8°C). Peripheral blood films showed disintegration of leukocytes and changes in their morphology after 12 hours of storage at room temperature and after 24 hours in refrigerated samples.

Conclusion:
Our study has shown that the results of some clinically important CBC parameters (WBC, HGB, PLT) remain stable for up to 72 hours after collection regardless of storage temperature. This may be important in certain clinical situations or for forensic reasons. However, some CBC parameters have a much shorter period of stability. It is therefore necessary to follow standards for specimen storage and handling in routine practice, which have been published by the Czech Society of Haematology ČLS JEP: The recommended maximum storage interval for CBC and differential counts were 5 hours at 15°C to 25°C.

Key words:
stability – complete blood count – leukocyte differential count – leukocytes – erythrocytes – platelets