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Updated: Dec 18, 2025
Analyzing Platelet Subpopulations by Multi-color Flow Cytometry
Published on: June 10, 2025
Flow cytometric evaluation of platelet-leukocyte conjugate stability over time: methodological implications of sample
Ayesha Singh1,2, Amanda R Coulter3, Patrick J Trainor3,4
1Division of Cardiovascular Medicine, University of Louisville School of Medicine, Louisville, KY, USA. ayesha.singh@louisville.edu.
Insights
Delays in staining blood samples significantly reduce measurements of platelet-monocyte conjugates (PMC) using flow cytometry (FCM). To ensure accurate results for acute coronary syndromes research, staining and FCM analysis should be completed within one hour of blood collection.
Area of Science:
- Cardiovascular Research
- Hematology
- Biomedical Engineering
Background:
- Platelet aggregation is crucial in atherothrombosis and acute myocardial infarction.
- Quantifying platelet aggregation aids in understanding acute coronary syndromes (ACS) pathogenesis.
- Circulating platelet-monocyte conjugates (PMC) measured by flow cytometry (FCM) reflect in vivo platelet aggregation.
Purpose of the Study:
- To evaluate the impact of sample handling variations on FCM measurements of PMC.
- To assess the stability of PMC concentrations under different fixation and immunolabeling intervals.
- To investigate the effects of Time-to-Fix and Time-to-Stain on FCM-based PMC quantification.
Main Methods:
- Investigated the effect of Time-to-Fix (3, 30, 60 min) and Time-to-Stain (1, 24, 48 h) on PMC measurements.
- Utilized flow cytometry (FCM) to quantify circulating platelet-monocyte conjugates (PMC).
- Conducted the study on five healthy volunteers.
Main Results:
- Increasing Time-to-Stain significantly reduced PMC measurements (p < 0.0001).
- No statistically significant difference in PMC measurements was observed with increasing Time-to-Fix (p < 0.41).
- Delays in staining compromised PMC measurements by 30% within 24 hours.
Conclusions:
- Postponing sample staining negatively impacts PMC measurement accuracy via FCM.
- Sample staining and FCM analysis should ideally be completed within one hour of blood collection.
- Standardized sample handling protocols are critical for reliable PMC quantification in ACS research.
Abstract:
Platelet activation and subsequent aggregation is a vital component of atherothrombosis resulting in acute myocardial infarction. Therefore, quantifying platelet aggregation is a valuable measure for elucidating the pathogenesis of acute coronary syndromes (ACS). Circulating platelet-monocyte conjugates (PMC) as determined by flow cytometry (FCM) are an important measure of in vivo platelet aggregation. However, the influence of sample handling on FCM measurement of PMC is not well-studied. The changes in FCM measurement of PMC with variation in sample handling techniques were evaluated. The stability of PMC concentrations over time with changes in fixation and immunolabeling intervals was assessed. The effect of Time-to-Fix and Time-to-Stain on FCM PMC measurements was investigated in five healthy volunteers. Time-to-Fix (i.e., interval between phlebotomy and sample fixation) was performed at 3, 30, and 60 min. Time-to-Stain (i.e., time of fixed sample storage to staining) was performed at 1, 24, and 48 h. Increasing Time-to-Stain from 1 to 24 or 48 h resulted in lower PMC measures (p < 0.0001). A statistically significant difference in PMC measurement with increasing Time-to-Fix was not observed (p < 0.41). Postponement of sample staining has deleterious effects on the measurement of PMC via FCM. Delays in immunolabeling of fixed samples compromised measurement of PMC by 30% over the first 24 h. Staining/FCM should be completed within an hour of collection.
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