Measurement of immature platelets with Abbott CD-Sapphire and Sysmex XE-5000 in haematology and oncology patients

Abstract

Background: Measurement of immature platelets was introduced into routine diagnostics by Sysmex as immature platelet fraction (IPF) some years ago and recently by Abbott as reticulated platelet fraction (rPT). Here, we compare both methods. Methods: We evaluated the precision and agreement of these parameters between Sysmex XE-5000 and Abbott CD-Sapphire in three distinct thrombocytopaenic cohorts: 30 patients with beginning thrombocytopaenia and 64 patients with recovering platelets (PLT) after chemotherapy, 16 patients with immune thrombocytopaenia (ITP) or heparin-induced thrombocytopaenia type 2 (HIT) and 110 additional normal controls. Furthermore, we analysed, how IPF/rPT differed between these thrombocytopaenic cohorts and controls. Results: Both analysers demonstrated acceptable overall precision (repeatability) of IPF/rPT with lower precision at low PLT counts. IPF/rPT artificially increased during storage of blood samples overnight. Inter-instrument comparison showed a moderate correlation (Pearson r² = 0.38) and a systematic bias of 1.04 towards higher IPFvalues with the XE-5000. IPF/rPT was highest in recovering thrombopoesis after chemotherapy and moderately increased in ITP/HIT. The normal range deduced from control samples was much narrower with CD-Sapphire (1.0%-3.8%, established here for the first time) in comparison to XE-5000 (0.8%-7.9%) leading to a smaller overlap of samples with increased PLT turnover and normal controls. Conclusions: IPF and rPT both give useful information on PLT turnover, although the two analysers only show a moderate inter-instrument correlation and have diffe rent reference ranges. A better separation of patient groups with high PLT turnover like ITP/HIT from normal controls is obtained by CD-Sapphire.

Reticulated platelets: analytical aspects and clinical utility

“…In the CELL-DYN Sapphire, the correlation between retPLT and MPV was investigated in relatively small groups and was described as not significant [64] or only weak [63]. However, in a large group of subjects with normal platelet counts, we found a significant negative correlation between retPLT and MPV [62].…”

“…Sapphire was found to have a distinctively narrower reference range than XE-5000, enabling higher sensitivity for separating normal and abnormal patients [63].…”

“…This approach enables correcting for the sizedependent background fluorescence of platelets [39]. In healthy individuals, mean retPLT are between 1.4% and 2.2%, and reported reference ranges are 0.4%-2.8% [59], 0.4% to 4.45%-6.0% [60][61][62] and 1.0%-3.8% [63].…”

“…Direct comparison between Sysmex XE-2100 or XE-5000 IPF and CELL-DYN Sapphire retPLT resulted in weak or modest correlations [63,64]. Sapphire was found to have a distinctively narrower reference range than XE-5000, enabling higher sensitivity for separating normal and abnormal patients [63].…”

Platelet analysis in laboratory hematology

“…This is why the devices currently available, despite claims to the contrary, have a poor specificity for "reticulated" platelets even if the addition of RNAse is used as evidence and somewhat reduces the signal. Therefore, the expectations in the follow-up studies to the original publications with manual measurement on the flow cytometer [6][7][8][9][10][11][12] have not been met, or only partially, on routine equipment with a reticulocyte channel [13][14][15][16][17][18], since the Spearman correlation coefficients are only at about 0.6. This clinically valuable parameter of the increased premature platelet release has therefore rarely been incorporated into clinical decisions in the differential diagnosis of thrombocytopenia.…”