Study of autoimmune thrombocytopenia

Clinical information

Diagnostic Utility:

• This study investigates the presence of anti-platelet autoantibodies.
• It is requested in patients suspected of autoimmune origin thrombocytopenia.
• In some patients, the origin of thrombocytopenia, both acute and persistently chronic presentation (> 6 months), is the presence of reactive antibodies against their own platelets (autoantibodies).

Method:

Immunofluorescence technique, with flow cytometry reading.

A direct antiglobulin test (DAT) is performed, incubating the patient's platelets with different DAT (Polivalent, IgG, IgM) conjugated with FITC. This test is also called a Direct Test. The presence of IgG and/or IgM class autoantibodies is evidenced by reading the fluorescence intensity (MFI) by flow cytometry.

If the result of the Direct Test is positive, the presence of anti-platelet autoantibodies in the eluate (if a sufficient number of platelets are obtained) and free in the patient's serum is investigated, through an indirect DAT, or Indirect Test. The problem samples (eluate, serum, or plasma) are compared to platelets from a group O donor, and after washes, different DAT are added, reading the results by cytometry.

The study is completed with a platelet count in blood in EDTA and citrate and a microscope review of the blood smear.

Diagnostic Algorithm:

Results:

The results of the autoimmune thrombocytopenia study are:  

• Positive study: anti-platelet autoantibodies are detected; results compatible with autoimmune thrombocytopenia (IgG and/or IgM)
• Negative study: no anti-platelet autoantibodies are detected in the sample studied

Precautions:

In order to complete the study, samples must be correctly sent to the Immunohematology laboratory. The requested tubes are necessary to obtain a sufficient number of patient platelets to perform the Direct Test.

For paediatric patients, only EDTA tubes should be drawn, the maximum volume possible depending on the child's age.

Response Time:

10 working days

Specimen information

Sample: Peripheral blood
Tubes in adult patients:

• 6 tubes* of 10 ml of EDTA K3
• 1 tube of 5 ml of EDTA K3
• 1 tube of 5 ml of citrate
• 1 tube of 5-10 ml without anticoagulant (serum)

* If the patient's degree of thrombocytopenia is known, the volume of blood in EDTA to be drawn can be adjusted. As a guideline, it is recommended:

Tubes in paediatric patients:

• Only EDTA K3 tubes, volume according to the child's age (minimum 5 ml)

Stability:

• At room temperature or at 4ºC: 3 days

Transport instructions: Preferably at room temperature
Reason for rejection:

• Sample very hemolyzed
• Samples received in tubes different from those specified in this data sheet.

Administrative information

BST Code: 4810
Test Description: Study of Autoimmune Thrombocytopenia
Synonyms: Study of anti-platelet autoantibodies
Section: Immunohematology
BST Rate: Check the updated rates here.

Profiles:

Test 4810 Study of Autoimmune Thrombocytopenia is not included in any profile.

References

• Heikal NM, Smock KJ. Laboratory testing for platelet antibodies. Am J Hematol. 2013;88(3):218-21.

• Muñiz-Diaz E, Canals C, Montero R, et al. Métodos para el diagnóstico de las citopenias inmunes. In: Vives Corrons JL, editor. Manual de técnicas de laboratorio en Hematología. 4th ed. Barcelona: Elsevier Masson; 2014.

• Goubran H, Hart C, Othman I, Seghatchian J. Flow cytometry and immune thrombocytopenic purpura. Transfus Apher Sci. 2018 Dec;57(6):800-803. doi: 10.1016/j.transci.2018.10.018.

• Provan D, Arnold DM, Bussel JB, Chong BH, Cooper N, Gernsheimer T, et al. Updated international consensus report on the investigation and management of primary immune thrombocytopenia. Blood Adv. 2019 Nov 26;3(22):3780-3817. doi: 10.1182/bloodadvances.2019000812.