Distinguishing Dengue virus infection from other febrile thrombocytopenic illnesses such as leptospirosis or enteric fever is important but difficult, due to the unavailability of reliable diagnostic tests.

In recent years, rapid diagnostic tests have been developed for dengue, leptospirosis, and enteric fever; however, these tests suffer from a limited sensitivity in highly endemic regions, and apart from these microbiological tests, a complete blood count is also often requested in these patients.

Scientists at the University of Padjadjaran (Bandung, Indonesia) and their colleagues used fluorescence flow cytometry to quantitate new parameters including cells in the atypical lymphocyte area (AL), high-fluorescent lymphocyte counts (HFLC), immature granulocytes (IG), and immature platelets (IPF). They compared hematocytometry performed by a hematology analyzer in 93 adults with dengue, 11 with leptospirosis, and 6 with enteric fever infection, and in 28 healthy controls.

Hemocytometry was performed on venous blood collected in Ethylenediaminetetraacetic acid (EDTA) vacutainers and analyzed by the Sysmex XE-5000 automated hematology analyzer (Sysmex Corporation; Kobe, Japan). In patients suspected for dengue, hemocytometry was repeated in the critical and recovery phase of the infection, defined as the period within 48 hours after defervescence before platelet counts started to rise and as the period in which platelet counts started rising again, respectively. In patients in whom a clinical suspicion for one or more of these diseases existed, blood was collected at admission for blood cultures for the diagnosis of enteric fever, serology, and rapid testing for leptospirosis and/or molecular diagnostics and serology for dengue.

The total lymphocyte counts between patients with dengue, leptospirosis, and enteric fever showed significant overlap. However, in the patients with dengue, a high percentage of AL (%AL) and HFLC (%HFLC) were present, while this was not the case for leptospirosis and enteric fever. These parameters did not correlate with the severity of dengue infection. Patients with leptospirosis had a significantly higher absolute IG count (a-IG) and percentage (%IG) than patients with enteric fever or with dengue infection. The a-IG and %IG values in the latter groups were similar to the values in the control group. The highest %IPF was found in the patients with dengue, who also had the lowest platelet counts. Low %AL, %HFLC, and %IG supported a diagnosis of enteric fever.

The authors concluded that cells in the atypical lymphocyte flagging area, the high fluorescent lymphocyte count, immature platelets, and immature granulocytes are new hematological parameters that may help to differentiate between common causes of febrile illnesses with thrombocytopenia in dengue endemic areas. The study was published online on September 3, 2015, in the International Journal of Laboratory Hematology.

Related Links:
University of Padjadjaran
Sysmex Corporation