Capillary fragility test
The capillary fragility test is a test using a blood pressure cuff. The cuff is applied for five minutes to the arm of a person and inflated to a pressure halfway between the systolic and diastolic blood pressure. Petechiae within the circumscribed skin area are then counted 1 Ten petechiae per square inch is considered normal, ten to twenty, marginal. Petechiae that are more than twenty per square inch are beyond the acceptable normal range and therefore the test indicates positive to vitamin C deficiency or thrombocytopenia.
This test used to be incorporated by the WHO as part of the algorithm for the diagnosis of dengue fever.2 However, because of the low sensitivity of the test, this is no longer recommended in the recent WHO guidance in the classification test for dengue haemorraghic fever.