Tourniquet test
Encyclopedia
A tourniquet test determines capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...

 fragility. It is a clinical diagnostic
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...

 method to determine a patient's haemorrhagic
Bleeding
Bleeding, technically known as hemorrhaging or haemorrhaging is the loss of blood or blood escape from the circulatory system...

 tendency. It assesses fragility of capillary walls and is used to identify thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...

 (a reduced platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes.  The average lifespan of a platelet is normally just 5 to 9 days...

 count).

The test is defined by the WHO as one of the necessary requisites for diagnosis of Dengue fever
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...

. A blood pressure cuff is applied and inflated to a point between the systolic
Systole (medicine)
Systole is the contraction of the heart. Used alone, it usually means the contraction of the left ventricle.In all mammals, the heart has 4 chambers. The left and right ventricles pump together. The atria and ventricles pump in sequence...

 and diastolic blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

s for five minutes. The test is positive if there are 10 or more petechiae per square inch. In DHF the test usually gives a definite positive result with 20 petechiae or more.

This test does not have high specificity. Interfering factors with this test are women who are premenstrual, postmenstrual and not taking hormones, or those with sun damaged skin, since all will have increased capillary fragility.

The test remains an essential part of the assessment of a patient who may have dengue haemorrhagic fever.
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