Reliability of the DI-60 Digital Image Analyzer for Detecting Platelet Clumping and Obtaining Accurate Platelet Counts

Pseudothrombocytopenia caused by platelet clumping (PC) can lead to unnecessary platelet transfusions or underdiagnosis of hematologic neoplasms. To overcome these limitations, we assessed the capacity of the Sysmex DI-60 digital morphology analyzer (Sysmex, Kobe, Japan) for detecting PC and determining an accurate platelet count in the presence of PC. For this purpose, 135 samples with or without PC (groups Y and N, respectively) were processed by an examiner (a hematologic specialist) using both the Sysmex XN-9000 and DI-60 analyzers. Although the platelet aggregate (PA) and giant platelet (GP) counts reported by the DI-60 and the examiner exhibited strong correlations, they proved inadequate as effective indicators for screening samples containing PC. Between the PA and GP counts and four platelet indices (the platelet distribution width [PDW], mean platelet volume [MPV], platelet large cell ratio [P_LCR], and plateletcrit [PCT]) reported by the XN-9000, we observed statistically significant correlations (both overall and with group Y), but they were relatively weak. The platelet counts determined using the DI-60 and light microscopy in group Y showed substantial variations. Although the performance of the DI-60 was reliable for detecting PA and GP in smear images, such fixed areas are not representative of whole samples. Further, in the presence of PC, the resulting platelet counts determined using the DI-60 were not sufficiently accurate to be accepted as the final count.

Integration of an MC-80 Digital Image Analyzer With an Automated BC-6800Plus Hematology Analyzer Enables Accurate Platelet Counting in Samples With EDTA-Induced Pseudothrombocytopenia

Background

EDTA-induced pseudothrombocytopenia (PTCP) during whole blood collection requires significant laboratory resources to obtain accurate results. We evaluated platelet-deaggregation function in EDTA-induced PTCP and platelet-clump flagging by the BC-6800Plus hematology analyzer using integrated digital image analysis.

Methods

We prospectively collected 132 whole blood samples suspected of platelet clumping (102 in EDTA and 30 in sodium citrate) from 88 individuals. We compared platelet counts determined using the platelet count by impedance (PLT-I) function of the DxH 900 hematology analyzer and the PLT-I or optical platelet count (PLT-O) function of the BC-6800Plus. Platelet clumping was verified through manual inspection and the MC-80 digital image analyzer.

Results

Among the 132 whole blood samples, 43 EDTA samples showed platelet clumping. The DxH 900 PLT-I and BC-6800Plus PLT-I results demonstrated a strong correlation (r=0.711) for the EDTA samples but only a moderate correlation with the BC-6800Plus PLT-O results (r=0.506 and 0.545, respectively). The BC-6800Plus PLT-O results were consistent with the sodium citrate platelet counts, with a median dissociation rate of 102.5% (range, 74.9%-123.1%). The DxH 900 and BC-6800Plus analyzers had sensitivity values of 0.79 and 0.72, respectively, for platelet-clump flagging. When integrating the MC-80 digital image analysis results, the sensitivity of BC-6800Plus improved to 0.89 (standard mode) or 1.0 (PLT-Pro mode).

Conclusions

BC-6800Plus PLT-O measurement results are close to the actual values obtained by platelet deaggregation with PTCP samples. Integrating the BC-6800Plus with a digital imaging analyzer effectively improved the diagnosis of PTCP and reduced the requirement for additional laboratory procedures.

A Vortex Method to Disaggregate Platelets for Correct Counting in Pseudothrombocytopenia

Pseudothrombocytopenia (PTCP) refers to the aggregation of platelets in anticoagulant blood in vitro and causes a false lower platelet count (PLT). For the purpose to achieve an accurate PLT, we presented an alternative vortex method to disaggregate platelet clumps and consequently generate a reliable PLT without a second venous puncture for patients. PLT, mean-platelet-volume (MPV), red blood cells (RBCs), hematoglobin (Hb), hematocrit (Hct) and white blood cells (WBCs) were evaluated before and after vortex in 221 specimens with PTCP using vortex method, and the PLT was also compared with 85 specimens disaggregated by citrate method. Twenty control samples were used to investigate mixing effect on complete blood counts in normal samples. One thrombocytopenia specimen was used to evaluate reproducibility of vortex. The mean PLT, MPV, RBCs, Hb, Hct and WBCs of 20 control specimens pre-vortex were 260.7 ± 53.4 × 109/L, 11.65 ± 0.85, 4.87 ± 0.46 × 1012/L, 147.6 ± 13.8 g/L, 45.31 ± 4.04, 6.46 ± 1.41 × 109/L, and results of post-vortex were 252.9 ± 50.2 × 109/L, 11.66 ± 0.92, 4.95 ± 0.48 × 1012/L, 149.1 ± 13.8 g/L, 45.19 ± 4.03, 6.35 ± 1.36 × 109/L respectively. Specimens with platelet clumps using vortex mixer had higher PLT after mixing, the mean pre-vortex PLT was 54.3 ± 35.2 × 109/L, and after vortexing PLT increased to 157.5 ± 58.8 × 109/L (p < 0.05). MPV, RBCs, Hb, Hct and WBCs in 221 specimens were comparable before and after vortex mixing (all p > 0.05). Vortex method might disaggregate platelet clumps sufficiently in most PTCP specimens, and obtain a relatively reliable PLT without the need of a second venous puncture.

Transient pseudothrombocytopenia (PTCP) in the neonate due to the mother

Thrombocytopenia with platelet count <50×10⁹/L is common laboratory finding in a severely ill newborn in neonatal intensive care units (ICU). Neonates with severe thrombocytopenia are at risk of bleeding. Most dangerous is intracerebral hemorrhage (ICH) frequently leading to death or lifelong neurological sequels. Pseudothrombocytopenia (PTCP) is a rare in vitro phenomenon of falsely low platelet count determined on hematology analyzers due to platelet clumping in ethylenediaminetetraacetic acid (EDTA) anticoagulated blood. PTCP was also reported in pregnant women with isolated thrombocytopenia. EDTA-PTCP in the neonate due to the transplacental transmission of maternal antibodies has been reported only in a few cases. Although PTCP is rare phenomenon, it should always be excluded in newborns with isolated thrombocytopenia to avoid erroneous interpretation of platelet and leukocyte count, unnecessary laboratory investigation of false positive antiplatelet antibodies and needless platelet transfusions. We report on two cases of transient PTCP in a neonate due to transplacental transfer of maternal EDTA-dependent autoantibodies of IgG class from the same mother.

Pseudothrombocytopenia: a case of platelet satellitism and phagocytosis by neutrophils

Thrombocytopenia is a clinically important condition that can lead to several problems when not correctly diagnosed. A decrease of platelet counts due to an in vitro phenomenon, Pseudothrombocytopenia, can be misunderstood and unnecessarily treated. The present case study describes a 57-year-old male with a history of pancreas adenocarcinoma and a current Staphylococcus aureus infection without any signs or symptoms that could explain the low levels of platelets obtained after blood analysis. Blood smear evaluation detected both platelet satellitism and phagocytosis by neutrophils. As this sample was anticoagulated with ethylenediaminetetraacetic acid (EDTA), a new blood sample with citrate was analyzed. Platelet count was normal and no morphological abnormalities were detected. This case emphasizes the need for considering not only laboratory results but also the patient clinical information to guarantee the correct diagnosis and the best treatment possible.

Pseudothrombocytopenia in Patients with Scrub Typhus Infection

Pseudothrombocytopenia is an ex vivo EDTA-dependent artefactual thrombocytopenia, that has been described in association with several conditions. When EDTA-blood samples are drawn from patients with pseudothrombocytopenia and analysed by automated cell counters, low platelet counts are obtained (often below 50,000/mm³). However, simultaneous heparinised samples show normal platelet counts, and peripheral smears show no reduction in numbers of platelets. We report a series of 12 patients with scrub typhus infections and pseudothrombocytopenia. An association between these two entities has only recently been appreciated. It appears that pseudothrombocytopenia may sometimes accompany acute scrub typhus infections. The distinction between pseudothrombocytopenia and true thrombocytopenia is of great clinical relevance, as the former is merely a laboratory artefact, and does not require blood product transfusions despite apparently severe reductions in platelet counts. It is therefore important to recognise that apparent thrombocytopenia, especially in patients with an acute febrile illness due to scrub typhus, is not always true thrombocytopenia.

Platelet satellitism in autoimmune hemolytic anemia

Platelet satellitism is a rare phenomenon observed in blood smears obtained from blood anticoagulated with EDTA with an estimated frequency at 0.008%. It is characterized by platelet rosetting around neutrophils and in rare cases around other blood cells, which may causes pseudothrombocytopenia. Our case involves a 26-year-old female patient with autoimmune hemolytic anemia (AIHA). Blood smear with EDTA as an anticoagulant had platelet satellitism whereas the phenomenon was not observed in tubes with different anticoagulants (citrate, heparin) and capillary blood. This phenomenon was still observed four weeks after the patient's discharge. Furthermore, we discuss the possible pathophysiological mechanisms of platelet satellitism proposed in the literature. To our knowledge, this is the first case of platelet satellitism reported in AIHA.

A case report of sudden thrombocytopenia detected only by in vitro analysis

We experienced an unexpected thrombocytopenia detected only in vitro during radical prostatectomy for a 66-year-old patient. Thrombocytopenia with platelet aggregation was observed in a blood sample obtained using a heparinized syringe (not by ethylene diamine tetra-acetic acid tube). Although we could not exclude platelet agglutination in vivo, no thrombosis or coagulation disorder was observed. We changed the anti-coagulant in the arterial catheter carrier fluid (saline) from heparin to argatroban, and continued with the operation. No embolic complications were observed during the perioperative period. Although pseudothrombocytopenia or heparin-induced thrombocytopenia was highly suspected in the present case, we were not able to confirm which of the two developed. Multi-directional attention and care may be required for perioperative unexpected thrombocytopenia.

Autoimmune Thrombocytopenia Complicated by EDTA- and/or Citrate-Dependent Pseudothrombocytopenia

Background

Pseudothrombocytopenia (PTCP) is a well-known phenomenon. However, confusion may occur due to unusual characteristics.

Case Reports

Two patients with autoimmune thrombocytopenia (ITP) and long-lasting PTCP are described. Initially, only the diagnosis of ITP was confirmed. During observation, discrepancies were recognized between clinical findings and platelet counts. Re-examination resulted in the additional diagnosis of EDTA-dependent PTCP. Subsequently, the latter diagnosis was changed to citrate-dependent PTCP in both cases. Interestingly, PTCP was observed to change again and became recognizable in citrate or heparin, and only during the first 20-30 min following phlebotomy in EDTA specimens.

Conclusion

The incidence of concomitant ITP with PTCP might be higher than previously reported, and PTCP may have variable dynamics and characteristics.