Scientific calendar January

A 56-year-old male patient was hospitalised due to strong symptoms associated with his COVID-19 infection. The development of the haematological parameters measured on an XN-Series analyser was observed over a period of 33 days.

Upon admission (day 0), the CBC results revealed almost normal results, but only the red blood cells, haemoglobin and haematocrit were slightly above the reference intervals. The automated white blood cell differential showed a normal distribution apart from few lymphocytes with increased fluorescence signals visible in the upper part of the WDF scattergram.

Already on day 2, the leucocytosis was noted (WBC 14.65 x 10³/µL) with neutrophilia. However, the neutrophils did not show signs of activation (NEUT-RI 42.6 FI, NEUT-GI 153.6 SI within the reference intervals [6]).

On day 4, the WBC count reached 17.89 x 10³/µL, and the analyser indicated the presence of IG with the ‘IG Present’ flag because the percentage of these cells increased to 5.1%.

Leucocytosis developed to even higher numbers over the course of time, reaching levels of > 20.00 x 10³/µL on day 11 and > 30.00 x 10³/µL on day 17 with IG present. During these three weeks, the red blood cells, haemoglobin and haematocrit continuously decreased, whereas platelets remained within the reference range, although showing already a downward trend. On day 24, the first time a significant presence of NRBC was recorded with 280 cells/µL (0.7%) as well as an increase in neutrophil activation (NEUT-RI). The presence of around 2% NRBC was recorded for six consecutive days until a remarkable increase happened:

• day 31: 11% NRBC
• day 32: 47.2% NRBC
• day 33: 116.5% NRBC

On day 26, the platelets dropped the first time to below 100 x 10³/µL, reaching the nadir on day 33 with 31 x 10³/µL. A meta-analysis by Lippi et al. found that platelet count may be a simple, economic, rapid and commonly available laboratory parameter that could straightforwardly discriminate the severity in COVID-19 patients. Moreover, it was observed that thrombocytopenia is also associated with threefold enhanced risk of severe COVID-19 [7].

Critically ill patients with respiratory infections can develop acute respiratory distress syndrome (ARDS), a severe complication and potentially life-threatening condition. Hence, reliable prognostic tools to predict respective outcomes early on are highly desired by clinicians [1].

Nucleated red blood cells (NRBC) are the progenitor cells of the red blood cells, which are absent in the peripheral blood of healthy adults. Under haemopoietic stress, however, NRBC can be found in the peripheral blood, since the bone marrow also releases the red blood cell lineage in the premature stages. When NRBC are present in blood of critically ill patients, this is generally associated with increased mortality [2]. Interestingly, NRBC positive patients showed significantly lower levels of arterial oxygen partial tension during intensive care treatment than NRBC negative patients [3]. Lower arterial oxygen partial tension has been found to indicate the future presence of NRBC. Moreover, findings in critically ill patients suffering from ARDS suggest that NRBC are equally predictive in ARDS mortality [4]. Additionally, in patients with acute pancreatitis, immature granulocytes (IG) could facilitate the identification of patients with a high risk of developing ARDS [5]. IG was judged as a potential indicator of ARDS incidence and has shown predictive power similar with (or greater than) other biomarkers.

The recent SARS-CoV-2 pandemic put a strain on hospitals and especially intensive care units which had to cope quickly with the rising numbers of hospitalised COVID-19 patients.

To emphasise this bottleneck and support hospitals with the management of COVID-19 patients, the COVID-19 prognostic score was developed [1]. The score is based on 10 variables, available directly or indirectly from the XN-Series analysers, which are weighted with points according to the measured result
(see Table 1).

Score values generated within the first three days of hospital admission can predict clinical severity in COVID-19 patients over the following two weeks. The score performance was shown to be superior to single parameters or parameter ratios.

Table 1 Overview of haematological variables utilised for the COVID-19 prognostic score.