The ligation test is essentially a test to assess the strength of the vessel wall, which is mainly the capillary wall. The ligation test can be used for early diagnosis of dengue, but it is not a specific sign of dengue fever, it can be positive in cases such as: meningococcal bacteremia, heterogenous capillaritis reactions, deficiency of coagulation factors, primary thrombocytopenia, disseminated intravascular coagulation…

Currently, many people misunderstand the sign of the ligature (Lacet is positive – Lacet in French is a knot) as a characteristic sign for the diagnosis of Dengue fever. The leash sign is defined on wikipedia as follows:

“Le test du lacet, ou signe du lacet, est un examen permettant une évaluation de la résistance ou de la fragilité des vaisseaux capillaires sanguins.”

Thus, the ligation sign (ligament test) is essentially a test to assess the strength of the vessel wall, which is mainly the capillary wall.

I. Principle of the ligation test:

Impede circulation to the heart to increase pressure in the venous lumen thereby increasing capillary pressure; then reduce the pressure suddenly. If the vessel wall is less stable, the red blood cells will be pushed out of the vessel wall causing subcutaneous hemorrhage in the form of small petechiae.

II. Steps to perform the ligature test

– Check the patient’s hand for bleeding (If any, it should be specified to distinguish it from new bleeding after the technique)

– Measure the patient’s blood pressure.

Maintain pressure with a sphygmomanometer at the average value between systolic and diastolic blood pressure for 10 minutes.

Quickly remove the sphygmomanometer, raise the patient’s hand to allow normal blood circulation.

III. Comment on the results of the ligature test

Observe the front of the arm and forearm below the ligature, count the number of hemorrhagic nodules (dots) per 1cm². Depending on the number of hemorrhagic nodules, people evaluate:

• 5-9 notes / 1cm²: suspect / positive (+)

• 10-19 notes / 1cm²: positive (++)

• > 19 notes / 1cm^2: positive (+++)

Characteristics of hemorrhagic nodules: usually about a few millimeters in diameter, can be larger but not more than 1cm, red, flat to the skin surface, pressing the slide or tightening the skin does not disappear and disappears in 2-5 day.

IV. Meaning of the ligation test:

• The ligation test can be used for early diagnosis of dengue, but it is not a specific sign of dengue fever, it can be positive in cases such as: meningococcal bacteremia, heterogenous capillaritis reactions, deficiency of coagulation factors, primary thrombocytopenia, disseminated intravascular coagulation…

• According to a Thai study, the positive ligation test combined with BC < 10 G/l, Hct > 40%, the specificity and positive diagnostic value is up to > 90%.

• When the results of the test are in doubt, further tests should be done to confirm the diagnosis of dengue.

• The ligation test is a simple and easy measure, but should be done at health facilities, people should not do it on their own and draw conclusions about the results of this test.

V. Common mistakes

– Mistaken with old hemorrhagic nodules, due to not checking or not checking carefully;

– Pressure is too high or too low;

– Time to increase pressure is not guaranteed.

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