Abstract
Platelet refractoriness continues to be a problem for thrombocytopenic patients because the risk of a major spontaneous or life-threatening bleed significantly increases when platelet counts drop below 10 × 109/L. The majority of patients have nonimmune causes driving the refractoriness, such as bleeding, medications, or diffuse intravascular coagulation; however, this article is dedicated to the diagnosis and support of patients with immune-based platelet refractoriness. Antibodies to class I HLA molecules (A and B alleles) are responsible for most immune-based refractory cases, with antibodies to platelet antigens seen much less frequently. Patients may be supported with either crossmatch-compatible or HLA-matched/compatible platelet units. When trying to select HLA units it can be difficult to find a perfect "4 of 4" match for the patient's class IA and IB alleles. In these cases, it is better to use the antibody specificity prediction method, which identifies compatible units that lack antigens recognized by the patient's anti-HLA antibodies. For an algorithmic approach to the patient with platelet refractoriness, see Visual Abstract.