Indian Pediatrics 2001; 38: 477-481
Hematological observations as diagnostic markers in dengue hemorrhagic fever - a reappraisal
DENGUE virus infection is known to exist in India for a long time. The first major outbreak of dengue hemorrhagic fever (DHF) was reported from Calcutta in 1964(1) followed by an epidemic in Vishakapatnam in 1965(2). Delhi had its major outbreak of dengue infection in 1988(3,4). After a long gap of 8 years a large outbreak of serious nature occurred in Delhi in 1996. During this outbreak, 304 cases of DHF were admitted to a major hospital in East Delhi. The present communication documents the observations on clinico-hematological parameters during epidemic with an intent to evaluate: (i) the utility of tourniquet test, (ii) association of bleeding manifestations with platelet count; and (iii) cut-off value of hematocrit, diagnostic of DHF in Indian population.
Three hundred and four patients aged 1-12 years of dengue hemorrhagic fever admitted to a tertiary care hospital during September 1996 to December 1996 were prospectively studied. The diagnosis of DHF was based on clinical criteria set by WHO which included: (a) high fever of acute onset, continuous in nature and lasting 2-7 days (b) hemorrhagic manifesta-tions including at least a positive tourniquets test, (c) hepatomegaly, and (d) symptoms of shock. The laboratory parameters taken were presence of thrombocytopenia (<100,000/mm3) and hematocrit increase of 20% or more of normal value. The first two clinical criteria plus thrombocytopenia and hemoconcentration or rising hematocrit established the diagnosis of DHF(5). Blood samples from clinically diagnosed DHF/ dengue shock syndrome (DSS) patients were tested for the presence of IgM antibodies to dengue virus using specific monoclonal anti-bodies to different serotypes by capture ELISA method (Mac-ELISA)(6). The sampling was done randomly on every fourth admitted patient. A total of 75 such samples were tested by this method.
Data pertaining to tourniquet test, hemato-crit concentration and effect of thrombo-cytopenia (platelet count less than 10,000/mm3) on bleeding manifestations was evaluated. Tourniquet test was performed by placing the sphygmomanometer cuff around the upper arm and raising the pressure to 100 mm Hg for 5-7 minutes. If pressure was <100 mm Hg, the pressure was raised half way between systolic and diastolic pressure for the same duration. The test was considered positive when more than 20 petechiae appeared in an area of 3 cm diameter 1 cm below the cubital fossa(7). Hematocrit concen-tration and platelet count were estimated using T890 coulter counter. The platelet count obtained from coulter counter was further confirmed by peripheral smear examination. The effect of thombocytopenia on bleeding was analyzed using chi square test. The hematocrit of DHF patients and hematocrit of normal children in the age group of 6-12 years calculated by the present workers was compared. The comparison was considered appropriate since the normal individuals were of the same geographical area. To find out "cut-off" hematocrit value diagnostic of dengue haemorrhagic fever, discriminant analysis was applied by taking observed proportions of cases in each group as an estimate of prior probability. The un-standardized canonical discriminant function coefficient was estimated to calculate discriminant scores. Various hematocrit values with their sensitivity and 1-specificity were used to construct ROC Curve. By constructing ROC curve the hematocrit with optimum sensitivity and specificity was arrived at (Fig. 1). Statistical computer analysis was carried out using software SPSS/PC+ version 5.0.
Fig. 1. Sensitivity and specificity of various hemato-crit values.
Three hundred and four patients were admitted during the study period of which 170 were males and 134 were females. The age range was 1 year to 12 years with maximum (78.9%) cases occuring in the age group of 6-12 years. The manifestation as dengue shock syndrome was noticed in 20% children (60/304). The case fatality rate of the present series was 4.8%. Out of a total of 75 sera samples, 57 tested positive for IgM antibodies to Dengue 2 serotype suggesting recent dengue infection. One sample had broadly reactive IgM anti-bodies suggesting recent flaviviral infection and 17 samples were negative for the anti-bodies.
Tourniquet test carried out on 239 clinically diagnosed cases was positive in 61 children only (25.5%). Similarly, the tourniquet test was positive in only 17 out of 58 serologically confirmed cases (29.3%). Association of single site bleeding with the platelet count was carried out. The difference of the proportion of bleeding manifestations among thrombocytopenic (Platelet count <100,000/mm3) and non-thrombocytopenic individuals was not statistically significant (Table I). Among the 58 serologically proven cases of DHF, 10/49 thombocytopenic children had no bleeding manifestations whereas 8/9 non-thrombocytopenic children had presented with bleeding (p = 0.45).
The mean and standard deviation of hematocrit value of 252 cases between the age of 1-12 years was 37.58 ± 6.81. However, for appropriate comparison, the hematocrit value of 202 DHF cases of 6-12 years of age was compared with hematocrit of 283 normal children of the same age group obtained from the same geographical area. The mean hematocrit value of 202 dengue patient and of 283 healthy children was 38.34 ± 6.02 and 32.03 ± 2.98%, respectively. A cut-off value of 36.3% was estimated by discriminant analysis which correctly classified 80% of cases. The sensitivity and specificity of this cut off value was 60% and 94%, respectively. The specificity of these values increased with rising hematocrit above 36.3% but sensitivity declined further. Hence, increased hematocrit concentration above the stated value can be considered as one of the diagnostic criteria of DHF.
Table I__Association of Bleeding Manifestations and Platelet Count
DHF is an acute illness characterized by fever, hemorrhagic manifestations and often circulatory failure. Thrombocytopenia and hemoconcentration are distinctive laboratory findings. The present study intends to highlight the associations of effect of thrombocytopenia on bleeding manifestations and to find out the sensitivity of tourniquet test. It also attempts to define the cut-off hemotocrit value diagnostic of dengue haemorrhagic fever in Indian population which has been hitherto unreported.
The results suggest that the bleeding manifestations were not effected by thrombo-cytopenia alone signifying that there may be other factors like platelet dysfunction and disseminated intravascular coagulation res-ponsible for bleeding(8,9).
Tourniquet test though considered an important diagnostic parameter was not found to be senstitive in the present study. This finding is in conformity with some other workers(10). The test needs to be reevaluated on a larger sample.
A high hematocrit value is the first abnormality in DHF due to leakage of plasma. Increase in hematocrit concentration by more than 20% of the baseline is an important diagnostic criterion(11). A cut-off value of hematocrit estimated in the present study has its significance due to pre-existent high prevalence of anemia in the community(12,13). Moreover, increase in hematocrit of 20% of baseline presents certain difficulties as initial value is usually not available(1). It is true that conditions like complicated enteric fever, leptospirosis, lymphoreticular malignancies can present with rising hematocrit and thrombocytopenia. However, one needs to carry out studies in such diseased states also to reach to a conclusive evidence. Furthermore, hematorcrit more than 36.3% labelled as the cut-off value diagnostic of DHF increased the specificity but further decreased the sensitivity to pick up cases of DHF.
The negativity of 17 samples for dengue serology by Mac-Elisa method may have been due to collection of blood sample within 5 days of diagnosis. The serology becomes positive only if sample is taken after 5 days of the onset of disease(14).
In conclusion, this study highlights no direct relationship of bleeding manifestations with the platelet count and poor sensitivity of tourniquet test in the diagnosis of DHF. It also attempts to define the cut-off hematocrit value diagnostic of DHF in Indian population.
We gratefully acknowledge the help of Dr. J.P. Thakre and Dr. Banerjee of National Institute of Virology, Pune, India for performing Mac-Elisa on our samples and providing the test results. Mr. Rajiv Kumar of Division of Biostatistics and Medical Informatics, University College of Medical Sciences, Delhi providing expertise for statistical analysis.
Contributors: SG coordinated the study, particularly its design and interpretation and drafted the paper; he will act as the guarantor of the article. VGR was instrumental in serodiagnosis of reported cases. SK, KNA, Piyush Gupta, DKD and PG were involved in data collection and help in drafting.
Competing interests: None stated.