The tourniquet test can be used to evaluate a patient's tendency to form petechiae due to defects in platelets and/or capillaries. The presence of increased venous pressure in a patient with thrombocytopenia or capillary fragility will increase the capillary pressure and result in petechiae.
(1) Mark a circle on the forearm. This is often 1 inch (2.5 cm) in diameter but some use a larger circle.
(2) Mark any pre-existing skin lesions.
(3) Inflate a sphyngmomanometer about the upper arm to a pressure midway between the systolic and diastolic blood pressures.
(4) Leave the cuff inflated for several minutes, then deflate it. The time of pressure application varies, and may range from 5, 10 or 15 minutes.
(5) The patient should not be left unattended during the test. If a large number of petechiae appear, then the test may need to be terminated early.
(6) Wait a few minutes to allow all petechiae to appear. Count the number of petechiae within the test area.
Interpretation:
• Most patients will form no or rare petechiae.
• The cutoff for a positive test varies on a number of factors, such as the desired sensitivity and specificity, the duration that pressure is applied, and the size of the test area.
• Some use >= 5 petechiae after a 5 minutes application period, while others use >= 10 petechiae for a 15 minute application period.
Limitations:
• The test has significant variability, with a large number of variables that are hard to control. The test may be useless if done incorrectly.
• Different areas of the arm may show different number of petechiae. If only 1 area is examined then the fragility may be over or underestimated. It is probably reasonable to count several areas and average the number.
• An arm can only be used every 1 or 2 weeks.
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