Abstract:
Identification of dengue hemorrhagic fever (DHF) at an early stage of the disease could
unravel many issues in clinical management of severe dengue. Thus, the main objective of
this study is to seek the prognostic value of Serum nitrite, a secondary stable intermediate
of nitric oxide in severe (DHF) and mild dengue fever (DF) patients along with its
association with serum IgM antibody levels. Clinically confirmed DHF (n=40) and DF (n=60)
patients were selected from Colombo North Teaching hospital (CNTH), Ragama, excluding
patients with previous dengue episodes and other infectious and non-infectious diseases.
Blood samples were collected at different stages of disease; admission (A), critical (C) and
discharge (D). Disease was confirmed by detection of NS1 antigen and IgM levels were
measured using commercially available quantifying ELISA kit. Griess assay was carried
out for deproteinized sera to seek the nitrite levels. Results showed significantly higher
serum nitrite level in DHF-A (mean ± SD, 1.535 ± 0.705 μM) compared to DF-A (1.240 ±
0.475 μM, independent sample t test, p=0.027). ROC curve analysis between DF-A and
DHF-A showed 62.6% area under the curve (p=0.036). Cut off value for serum nitrite in
DHF-A was determined as 1.255 μM with 63.9% sensitivity and 60.5% specificity.
Moreover, DHF-A has significantly higher nitrite value compared to DHF-D (paired sample
t test, p=0.006). Thus, these results postulate that high levels of nitrite in DHFA may be due
to high production of nitric oxide associated with pathogenesis of severe dengue and higher
expression of inducible nitric oxide synthase enzyme (iNOS). Analysis of IgM revealed
significantly higher levels of antibodies in DF (75.71 ± 47.42 U/ml) compared to DHF (52.21
± 36.20 U/ml) (p=0.045) patients, implying IgM may be playing a protective role in DF.
However, no significant association was obtained between IgM and nitrite levels in each
patient category. Nevertheless, other studies have shown that in severe dengue, antibodies
produced against NS1 antigen could bind endothelial cells which enhance the release of
nitric oxide causing cell apoptosis. Lack of association between IgM and nitrite levels
observed here indicate that there may be other mechanisms contributing to DHF.
Keywords: Dengue hemorrhagic fever, reactive nitrogen species, IgM antibodies
