LAUSR

Dear Editors, Several reports have been published describing that eosinopenia is a common finding in COVID19 patients.1,2 In this journal, Soni3 presented a very interesting study, showing that eosinopenia on admission is a reliable and convenient early marker for COVID19 infection. The specificity was as high as 100% in this study population. The author states that these findings need to be corroborated with a larger, multicentre study. With regard to patient logistics (eg singlepatient rooms) and laboratory costs, especially in lowresource settings, it would be of great value to have a fast alternative test for the SARSCoV2 reverse transcription polymerase chain reaction (RTPCR). In the southern part of the Netherlands, the first COVID19 patients were admitted to hospitals in early March 2020. In the Dutch first wave, a high incidence rate was observed in the southeast where the three general hospitals (EH, JBH and SJG) participating in this study are located. The cell counts in these three hospitals were determined using the ADVIA 2120i haematology analyser (Siemens Healthineers, The Netherlands). The ADVIA 2120i haematology analyser accurately separates eosinophils from other leucocytes using peroxidase activity measurement and nuclear density cytograms. In line with the published study by Soni, patients with a positive test result of the SARSCoV2 RTPCR were considered as confirmed COVID19 cases. Although the performance of SARSCoV2 RTPCR testing is highly accurate, a certain number of falsenegative test results cannot be ruled out.4 Data at admission to the hospital were collected from the records of 2064 patients, including eosinophil count and result of SARSCoV2 RTPCR (723 RTPCR– positive; 1341 RTPCR– negative). The mean eosinophil count in the confirmed COVID19 patients was very low (0.03 × 109/L), but higher than the median reported by Soni (0.01 × 109/L). During 2019 (pre– COVID19), the mean eosinophil count in our region was 0.200 × 109/L, and in our RTPCR– negative group, 0.139 × 109/L, both lower than the median in the RTPCR– negative group (0.25 × 109/L) reported by Soni.2 In Figure 1, the percentage of patients with an eosinophil count below the cutoff as proposed by Soni (0.05 × 109/L) is presented during 2019 (pre– COVID19) until week 7 2021. Additionally, the percentage of weekly admissions of SARSCoV2 RTPCR– positive patients is shown. There is a clear correlation between COVID19 admissions and number of patients with very low eosinophil counts. It is shown that during the Dutch winter period in 2019 elevated number of low eosinophil counts can be observed as well. We speculate that this observed eosinopenia is a result of infection with other commonly occurring respiratory viruses. As shown in Table 1, using the cutoff 0.05 × 109/L, the sensitivity was 83.3% (Soni study: 80.7%), but the specificity was merely 64.1% (Soni study: 100%). In our patient population, the PPV was 55.6% and NPV 87.7% (Soni study: 100% and 61.5%, respectively). The accuracy was 70.8% (Soni study: 85.2%). Unfortunately, we were not able to confirm the study findings published by Soni.2 We notice that the separation of the RTPCR– positive and RTPCR– negative patient groups in our