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Home :: Capillary fragility

Capillary Fragility

Also called the tourniquet test, the capillary fragility test is a nonspecific method for evaluating bleeding tendencies. A positive-pressure test, used to measure the capillaries ability to remain intact under increased intracapillary pressure, is controlled by a blood pressure cuff around the patient's upper arm.

Purpose

  • To assess the fragility of capillary walls.
  • To identify a platelet deficiency (thrombocytopenia).

Patient preparation

  • Explain to the patient that this test is used to identify abnormal bleeding tendencies.
  • Tell him who will perform the procedure and when.
  • Inform him that food or fluids need not be restricted.
  • Explain that he may feel discomfort from the pressure of the blood pressure cuff.

Procedure and posttest care

  • The patient's skin temperature and the room temperature should be nor. mal to ensure accurate results.
  • Select and mark a 2" (5-cm) space on the patient's forearm. Ideally, the site should be free of petechiae; otherwise, record the number of petechiae present on the site before starting the test.
  • Fasten the cuff around the arm, and raise the pressure to a point midway between the systolic and diastolic blood pressures (approximately 100 mm Hg). Maintain this pressure for 5 minutes; then release the cuff.
  • Count the number of petechiae that appear in the 2" space.
  • Record test results.
  • Encourage the patient to open and close his hand a few times to hasten return of blood to the forearm.
Precautions
  • Do not repeat this test on the same arm within 1 week.
  • This test is contraindicated in patients with disseminated intra vascular coagulation (DIC) or other bleeding disorders, and in those with significant petechiae already present.

Reference values

A few petechiae may normally be present before the test. Less than 10 petechiae on the forearm 5 minutes after the lest is considered normal, or negative; more than 10 petechiae is considered a positive result. The following scale may also be used to report test results.

NUMEBER OF PETECHIAE/5 CM
SCORE
A few on anterior forearm
1+
Many on anterior forearm
2+
Many on whole arm and top of hand
3+
Confluent petechiae on all areas of arm and top of hand
4+
Abnormal findings

A positive finding (more than 10 petechiae or a Score of 2+ to 4+) indicates weakness of the capillary walls (vascular purpura) or a platelet defect. It may occur in such conditions as thromboccytopenia, thrombasthenia, purpua senilis, scurvy, DIC, von Willebrand's disease, vitamin K deficiency, dysproteinemia, and polycythemia vera and in severe deficiencies of factor VII, fibrinogen, or prothrombin. Conditions unrelated to bleeding defects, such as scarlet fever, measles, influenza, chronic renal disease, hypertension, and diabetes with coexistent vascular disease, may also increase capillary fragility. An abnormal number of petechiae sometimes appear before menstruation and at other times in some healthy persons, especially in women over age 40.

Interfering factors

  • Decreasing estrogen levels in postmenopausal women (possible increase)
  • Glucocorticoids (possible decrease)
  • Repeating the test on the same arm within 1 week, causing errors in counting the number of petechiae.
  • Overinflation or underinflation of the cuff.

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