Enhanced Accuracy of Optical Platelet Counts in Microcytic Anemia

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.

Unreliable Automated Complete Blood Count Results: Causes, Recognition, and Resolution

Automated hematology analyzers generate accurate complete blood counts (CBC) results on nearly all specimens. However, every laboratory encounters, at times, some specimens that yield no or inaccurate result(s) for one or more CBC parameters even when the analyzer is functioning properly and the manufacturer’s instructions are followed to the letter. Inaccurate results, which may adversely affect patient care, are clinically unreliable and require the attention of laboratory professionals. Laboratory professionals must recognize unreliable results, determine the possible cause(s), and be acquainted with the ways to obtain reliable results on such specimens. We present a concise overview of the known causes of unreliable automated CBC results, ways to recognize them, and means commonly utilized to obtain reliable results. Some examples of unreliable automated CBC results are also illustrated. Pertinent analyzer-specific information can be found in the manufacturers’ operating manuals.

Alinity hq platelet count is not impacted by severe microcytosis

Background

Impedance technology has been shown to overestimate platelet (PLT) count in samples with microcytes, while the optical‐fluorescence PLT count (PLT‐F) by Sysmex has been suggested to be unaffected by microcytosis. The Abbott Alinity hq analyzer employs multi‐dimensional optical PLT counting. Our goal was to assess the accuracy of this technology in microcytic samples.

Methods

Platelet measurements were performed by Alinity hq and the impedance (PLT‐I) and PLT‐F methods on a Sysmex XN‐3000 analyzer on 464 samples. PLT concentration range was 6.56–947 × 10⁹/L and mean cell volume (MCV) 40.9–123.0 fL. Samples were categorized into normocytic (MCV > 80 fL), microcytic (MCV 65–80 fL), and severely microcytic (MCV < 65 fL) groups.

Results

Alinity hq PLT count showed excellent agreement with PLT‐F (r = 1.00). Sysmex PLT‐I data showed somewhat weaker correlation with both PLT‐F and Alinity hq (r = 0.98). Increasing bias between Sysmex PLT‐I and PLT‐F was seen with decreasing MCV values, with mean bias of 35.2 × 10⁹/L in severe microcytosis. An inverse relationship was demonstrated between the PLT‐I versus PLT‐F bias and MCV (p < 0.0001). Consistent mean bias was observed between Alinity hq and PLT‐F across all MCV ranges.

Mean platelet volume was suppressed or flagged by Sysmex XN in 50% of the samples in the severely microcytic group, and markedly higher red cell distribution width (RDW) was reported compared to Alinity hq (18.1% vs 13.7%, p < 0.0001).

Conclusion

The Sysmex PLT‐I method overestimated the PLT count in samples with severe microcytosis. Alinity hq provided PLT counts and PLT and RBC indices that were not impacted by microcytosis.

Alinity hq platelet results are equivalent with the international reference method in thrombocytopenic samples

INTRODUCTION

Accurate and precise platelet (PLT) count is critical for the appropriate management of patients with thrombocytopenia. This study evaluated the performance of PLT counting with the Abbott Alinity hq hematology analyzer, which utilizes multi-dimensional optical technology.

METHODS

Imprecision, linearity, and accuracy were assessed per CLSI guidelines. Alinity hq PLT results were compared to the international flow cytometry reference method (IRM) in the concentration range of 6.3 to 103.0 × 10⁹ /L. Additional comparisons were made with Sysmex XN-3000 PLT counts: impedance (PLT-I), optical (PLT-O), and optical fluorescent (PLT-F) methods.

RESULTS

The average within-run %CV was 4.7% on patient samples with PLT concentrations ranging from 13.1 to 41.7 × 10⁹ /L, and the within-laboratory %CV was 3.6% at the level of 68.2 × 10⁹ /L. Linearity evaluation indicated a maximum deviation of 3.1% from the linear fit in the range of 0.1 to 316.8 × 10⁹ /L. Comparison between Alinity hq and the IRM PLT counts yielded a correlation coefficient of 0.99 and predicted bias of 0.0 and -0.5 × 10⁹ /L at 10.0 and 20.0 × 10⁹ /L transfusion thresholds, respectively. Alinity hq PLT counts also correlated well with Sysmex PLT counts, with strongest correlation obtained with PLT-F and PLT-O (r = .99) methods.

CONCLUSION

This study demonstrated excellent analytical performance of Alinity hq PLT counting in thrombocytopenic samples, equivalency with the IRM and strong agreement with Sysmex PLT-F and PLT-O methods. The Alinity hq multi-dimensional optical PLT count is available with every CBC without additional reagents and may help promote efficiency in clinical laboratories.

Performance Evaluation of Automated Impedance and Optical Fluorescence Platelet Counts Compared With International Reference Method in Patients With Thalassemia

CONTEXT

- Spurious platelet counts from automated methods have been reported in patients with abnormal red blood cells. However, there is no specific study regarding performance of platelet counts by automated methods in patients with thalassemia.

OBJECTIVE

- To investigate the performance of automated platelet counts, including impedance (PLT-I) and optical fluorescent (PLT-O and PLT-F) methods, and compare them with the international reference method (IRM) for platelet counting in patients with thalassemia.

DESIGN

- Two hundred forty-nine thalassemia specimens from various subtypes were examined. PLT-I, PLT-O, and PLT-F from a Sysmex XN analyzer were evaluated and compared against the IRM. Demographic data, platelet counts, and red blood cell parameters are shown. Comparability between evaluated methods and IRM, as well as test characteristics, is presented. Factors involving inaccurate PLT-I were analyzed.

RESULTS

- Specimens with platelet counts ranging from 31 × 10³/μL to 932 × 10³/μL were included. Most patients were patients with thalassemia major. Correlation between PLT-I and IRM was lower than that of the other methods in overall patients. PLT-O and PLT-F were correlated to IRM when classifying patients according to clinically significant platelet ranges. All automated methods had acceptable sensitivities; however, specificity of PLT-I was low for diagnosis of thrombocytopenia. High RDW-CV (red blood cell distribution width-coefficient of variation) was an independent factor of inaccurate PLT-I measurement.

CONCLUSIONS

- Among the evaluated methods, PLT-I was the method least correlated to IRM, with PLT-O and PLT-F comparable to IRM in patients with thalassemia. Optical platelet counts and careful blood smear examination are recommended alternative platelet counting methods, depending on the clinical setting.

Accuracy of Platelet Counting by Optical and Impedance Methods in Patients with Thrombocytopaenia and Microcytosis

OBJECTIVES

Obtaining accurate platelet counts in microcytic blood samples is challenging, even with the most reliable automated haematology analysers. The CELL-DYN(™) Sapphire (Abbott Laboratories, Chicago, Illinois, USA) analyser uses both optical density and electronic impedance methods for platelet counting. This study aimed to evaluate the accuracy of optical density and electrical impedance methods in determining true platelet counts in thrombocytopaenic samples with microcytosis as defined by low mean corpuscular volume (MCV) of red blood cells. Additionally, the impact of microcytosis on platelet count accuracy was evaluated.

METHODS

This study was carried out between February and December 2014 at the Haematology Laboratory of the Sultan Qaboos University Hospital in Muscat, Oman. Blood samples were collected and analysed from 189 patients with thrombocytopaenia and MCV values of <76 femtolitres. Platelet counts were tested using both optical and impedance methods. Stained peripheral blood films for each sample were then reviewed as a reference method to confirm platelet counts.

RESULTS

The platelet counts estimated by the impedance method were on average 30% higher than those estimated by the optical method (P <0.001). The estimated intraclass correlation coefficient was 0.52 (95% confidence interval: 0.41-0.62), indicating moderate reliability between the methods. The degree of agreement between methods ranged from -85.5 to 24.3 with an estimated bias of -30, suggesting that these methods generate different platelet results.

CONCLUSION

The impedance method significantly overestimated platelet counts in microcytic and thrombocytopaenic blood samples. Further attention is therefore needed to improve the accuracy of platelet counts, particularly for patients with conditions associated with microcytosis.