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The noose test is a quick test that must be performed in all cases of suspected dengue, as it allows identifying the fragility of blood vessels, common in dengue virus infection.
This test can also be known as tourniquet test, Rumpel-Leede test or simply capillary fragility test, and is part of the World He alth Organization recommendations for the diagnosis of dengue, although this test is not always be positive in people with dengue. It is for this reason that, after the positive result, a blood test should be performed to confirm the presence of the virus.
As it identifies the risk of bleeding, the loop test does not need to be used when there are already signs of bleeding, such as bleeding from the gums and nose or the presence of blood in the urine. In addition, the loop test may present false results in situations such as the use of aspirin, corticosteroids, pre- or post-menopause, or when there is sunburn, for example.
Positive loop test result
What is the exam for
The loop test is mainly known to help in the diagnosis of dengue, however, as it tests the fragility of the vessels, it can also be used when other diseases that can cause hemorrhages are suspected, such as:
- Liver diseases;
Since the loop test can be positive in many situations, after knowing the result it is always recommended to do other diagnostic tests, starting with blood tests, for example.
How the test is done
To do the loop test, you must draw, on the forearm, a square with an area of 2.5 x 2.5 cm and then follow these steps:
- Evaluate the person's blood pressure with the sphygmomanometer;
- Inflate the sphygmomanometer cuff again to the midpoint between maximum and minimum pressure. To find the average value, you must add the Maximum Blood Pressure to the Minimum Blood Pressure and then divide by 2. For example, if the blood pressure value is 120x80, the cuff must be inflated to 100 mmHg;
- Wait 5 minutes with the cuff inflated at the same pressure;
- Deflate and remove the cuff,after 5 minutes;
- Let the blood circulate for at least 2 minutes.
Finally, you should evaluate the number of reddish spots, called petechiae, inside the square on the skin to know the test result.
Understand what petechiae are and see other causes that may be at their origin.
How to understand the result
The result of the loop test is considered positive when more than 20 red dots appear inside the marked square on the skin. However, a result with 5 to 19 dots can already indicate suspicion of dengue, and other tests should be performed to help confirm whether or not the infection is present.
It is important to remember that the exam can be false negative even in people who have the disease, so if there is suspicion through the symptoms, the doctor should request other evaluations to confirm. In addition, it can be positive in other diseases that cause capillary fragility and risk of bleeding, such as other infections, immune diseases, genetic diseases or even the use of medicines such as aspirin, corticosteroids and anticoagulants, for example.
Thus, it can be seen that this test is not very specific and should only be performed to aid in the diagnosis of dengue. Learn more about the tests available to diagnose dengue.