In a tourniquet test for dengue, the blood capillaries are examined for their ability to withstand increased pressure. This gives a good indication for assessing the blood vessels and whether it will lead to Dengue Shock Syndrome (DSS) or Dengue Hemorrhagic Fever (DHF).
This test involves checking what are known as petechiae, i.e. small red spots under the surface of the skin. These petechiae are formed when blood leaks from capillaries into the skin. Pressing the petechiae does not have any effect on its appearance.
The old version of the test was to simply apply a tourniquet (any kind) for 5 minutes at the upper arm until red dots appear distal to it. A variety of factors had to be considered: the type of tourniquet, the pressure applied, and the results to determine if it is positive. So a standard was developed by medical schools of long ago:
This test is not considered to be completely reliable for confirming dengue. Factors that can influence the results are premenstrual and postmenstrual period in women and sun damaged skin in people. This is because all such people are sure to have relatively fragile capillaries. Dengue Tourniquet Test does have its use in diagnosis of dengue. It is useful in monitoring a patient’s condition when he is suffering from Dengue Shock Syndrome (DSS) or Dengue Hemorrhagic Fever (DHF).
The World Health Organization (WHO) has defined this test as one of the necessary requirements for dengue fever diagnosis. In case of Dengue Haemorrhagic Fever (DHF), the test generally gives a sure positive result with 20 or more petechiae per square inch. Since the test does not have high specificity i.e. ability to confirm the infection, the interfering conditions must be taken into consideration.
Premenstrual women, postmenstrual women who are not taking hormonal supplements, women having skin damaged by sun must not take this test as they have high capillary fragility due to altogether different reasons. Since dengue infection is typical of a tropical and sub-tropical country, the tourniquet test is used to evaluate the possibility of dengue infection immediately in such countries. There are 36 million symptomatic cases of dengue worldwide with 2.1 million severe cases reported in the year 2010. With a tourniquet test, people suspected of having contracted the infection can be immediately hospitalised for treatment and further diagnosis.
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