Fast detection and quantification of Plasmodium species infected erythrocytes in a non-endemic region by using the Sysmex XN-31 analyzer

Abstract

Background Due to increased travel from endemic countries, malaria occurs more frequently in non-endemic regions. It is a challenge for diagnostic laboratories in non-endemic countries to provide reliable results, as experience of staff is often limited to only a few cases per year. This study evaluated the diagnostic accuracy of the fully automated Sysmex XN-31 malaria analyzer in a routine diagnostic setting in a non-endemic region was evaluated. Methods Samples from 112 patients suspected for malaria were examined by the Sysmex XN-31 analyzer to determine the absolute count of malaria-infected red blood cells count (MI-RBC/µL). Microscopic examination of both Quantitative Buffy Coat capillary tubes and thick and thin blood films were used as reference methods. Limits of blank (LoB), detection (LoD) and quantification (LoQ) were investigated using an in vitro Plasmodium falciparum culture. Nine hundred twenty samples of patients with RBC abnormalities were included to determine which RBC abnormalities trigger indeterminate or false positive results. Results No false positive nor false negative results were obtained for the examined patient samples suspected for malaria. For 3% of samples an indeterminate result by the XN-31 was obtained. The Passing-Bablok regression line for diagnostic accuracy of the parasitaemia was y = 39.75 + 0.7892 × showing a positive bias of about 21% when comparing the MI-RBC results to microscopy. The LoB, LoD and LoQ were calculated to be 4.7, 5.9, and 19.0 infected RBC/μL, respectively. From the 920 abnormal RBC samples collected, 4.6% resulted in a false positive MI-RBC result and almost half of the samples produced indeterminate results. These results were related to increases in nucleated red blood cells, reticulocytes and other abnormal RBC morphologies such as sickle cells. Conclusions Based on the results, the XN-31 is a fast and reliable screening method in the detection and quantification of Plasmodium species in patients However, if an abnormal red blood cell morphology is present, the results of the XN-31 should be interpreted with caution as false positive results can be caused by interfering abnormal erythrocytes.

Clinical performance testing of the automated haematology analyzer XN-31 prototype using whole blood samples from patients with imported malaria in Japan

“…Thus, the LoD (limit of detection) of the LM mode of the XN-31p could be much lower than the LoQ value defined by the company. This result is consistent with a recent report [ 12 ] that estimated LoD and LoQ values for the LM mode of the XN-31 using cultured P. falciparum . Recently, asymptomatic malaria cases with low-density parasitaemia have been discussed as potential reservoirs for transmission in endemic areas [ 16 – 18 ].…”

“…The XN-31p means a prototype device before the release of the XN-31 commercially which has the same physical characteristics, hardware configuration, and reagent composition as does the XN-31p. For the XN-31p and the XN-31, their excellent performance as malaria diagnostics in clinical settings were also suggested in recent reports respectively [11][12][13].…”

“…The existence of reticulocytes, which may not have been correctly identified, might contribute to such abnormal patterns [ 10 ]. A recent study also showed that various RBC abnormalities cause “MI-RBC Abn Scattergram” and that these abnormalities sometimes even cause exact false-positive results by the XN-31 [ 12 ]. These patterns should be treated carefully and examined with other methods at clinical sites, and more examination is needed in future studies.…”

Evaluation of new haematology analyser, XN‐31, for malaria detection in blood donors: A single‐centre study from India

“…Few of these diseases/conditions are sickle cell disease, beta thalassemia, haemochromatosis premature newborns, etc. [13]. Though these individual diseases/conditions were not evaluated in the present study, it is possible that few of the samples in the present study cohort of ‘clinical samples’ had one of these underlying disease conditions, triggering false‐positive results in XN‐31.…”

Advances and challenges in automated malaria diagnosis using digital microscopy imaging with artificial intelligence tools: A review

“…New advances based on fluorescence flow cytometry have shown that the Sysmex XN-31 device can determine the Plasmodium species and quantify parasites in blood. However, it can generate false positive results in case of abnormal erythrocytes cell morphology and the device was tested in a non-endemic region ( Khartabil et al, 2022 ).…”