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Discrepancy in Optical and Impedance Platelet Count in Platelet Rich Plasma Prepared for Light Transmission Aggregation as a Possible Sample Quality Indicator

BACKGROUND Mechanical forces during platelet rich plasma (PRP) preparation can activate platelets that subsequently form platelet clumps. We have observed differences in platelet counts measured with optical (PLT-O) and impedance (PLT-I) method, performed prior to light transmission aggregation testing. Currently, there is no recommendation on the preferred method for platelet count determination. AIMS Aim was to explain observed differences by investigating platelet indices (PI) [mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (PLCR)] in PRPs with discrepant PLT-O and PLT-I counts compared to PRPs with consistent platelet counts. METHODS PRPs were prepared from 105 samples by centrifugation (200g, 10min). Platelet counts and PI were measured on Sysmex XE5000. Total allowable error (13.4%) based on biological variation was used to discriminate PRPs with significantly different PLT-I and PLT-O counts. Kolmogorov-Smirnov test, Bland-Altman analysis, paired samples- and independent t-test, and Pearson correlation test were used for statistical analysis. P<0.05 was considered significant. RESULTS PLT-O method gave consistently higher counts compared to PLT-I method (P<0.001) with a mean difference of 44.7x109/L (Figure 1). Neither PLT-O nor PLT-I count correlated with PI. 48% PRPs showed significant difference between PLT- O and PLT-I with lower MPV, PDW and PLCR (P<0.001 for all PI). All PI correlated weakly with the difference in PLT-I and PLT-O count (r=-0.37, r=-0.38, r=-0.35, respectively ; P<0.001). CONCLUSIONS The reason for discrepancies between PLT-O and PLT-I is not completely clear. Higher PLT-O counts could be due to platelet clumps that are only counted by optical method. Consequently, smaller platelets are counted using impedance method which explains lower PI in PRPs with discrepant platelet counts and greater difference between counts. This finding can be used as quality indicator of PRP prepared for aggregation testing.

platelet rich plasma ; light transmission aggregation testing

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