Causes of False Thrombocytopenia

In patients with polycythemia, using standard amounts of anticoagulant with reduced plasma volume can cause falsely low platelet counts, according to the American Heart Association, with a recommendation to adjust anticoagulant volume 1

Clinical Conditions That Can Mimic Thrombocytopenia

In cyanotic congenital heart disease, increased hematocrit reduces plasma volume, requiring adjustment of anticoagulant volume to avoid falsely low platelet counts, as suggested by the American College of Cardiology 1

False-negative results in testing for platelet alloantibodies can occur due to delayed appearance of antibodies or low-affinity antibodies, as reported by the International Society on Thrombosis and Haemostasis 2, 3
Testing for drug-induced thrombocytopenia may yield false-negative results if testing is performed after thrombocytopenia resolves or if a metabolite rather than the parent drug is responsible, according to the British Society for Haematology 4

Heparin-induced thrombocytopenia (HIT) has a characteristic temporal pattern (typically 5-10 days after starting heparin) and may be associated with thrombotic events, as described by the American Society of Anesthesiologists 5

La pseudotrombocitopenia es principalmente causada por la aglutinación plaquetaria in vitro dependiente de EDTA, que debe excluirse mediante el examen del frotis de sangre periférica antes de iniciar cualquier investigación o tratamiento para trombocitopenia verdadera 6, 7

Debe distinguirse de la trombocitopenia inducida por heparina (HIT), que presenta un patrón temporal característico y puede asociarse con eventos trombóticos 8, 9
Otras causas de trombocitopenia verdadera incluyen trombocitopenia inmune primaria (PTI) 6, 10
Infecciones como HIV y HCV pueden causar trombocitopenia verdadera 7, 10
Enfermedades autoinmunes como el lupus eritematoso sistémico pueden causar trombocitopenia 6, 7
Trastornos linfoproliferativos pueden causar trombocitopenia 6
Trombocitopenia inducida por fármacos es otra causa de trombocitopenia verdadera 7
Enfermedades de la médula ósea pueden causar trombocitopenia 7

The American Society of Hematology recommends that pseudothrombocytopenia be excluded by peripheral blood smear examination before initiating any investigation or treatment for true thrombocytopenia, as it is a laboratory artifact caused primarily by EDTA-dependent platelet agglutination in vitro 11, 12, 13
Evaluation of the peripheral blood smear by a qualified hematologist or pathologist is paramount and must be performed to exclude pseudothrombocytopenia before any further workup, according to the American College of Pathology 11, 12, 13, 14

The American College of Physicians recommends HIV and HCV testing in all adults with suspected immune thrombocytopenia regardless of risk factors, as well as H. pylori testing in adults where eradication may have clinical impact 11, 12, 14
Bone marrow examination is indicated for patients older than 60 years, those with systemic symptoms, or when splenectomy is considered, as recommended by the American Society of Hematology 11, 12, 14
A comprehensive drug history must be taken, including prescription medications, over-the-counter drugs, herbal supplements, quinine-containing beverages, and recent heparin exposure, according to the National Institutes of Health 13, 14