What is the prevalence of alloimmunized refractoriness to platelet transfusions?

Updated: Sep 08, 2017
  • Author: Douglas Blackall, MD, MPH; Chief Editor: Michael A Kaliner, MD  more...
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Answer

Approximately 20-85% of patients who receive multiple transfusions become immunized to platelet antigens (eg, HLA, HPA), and 30% of patients who are alloimmunized develop refractoriness to platelet transfusions.

Overall, platelet refractoriness occurs in approximately 20-70% of patients who receive multiple transfusions. In two-thirds of these patients, nonimmune factors (see Differentials) alone are the cause, whereas alloimmunization may be involved in one-third of refractory patients, often in combination with nonimmune causes.

HLA class I antibodies are implicated in most alloimmunization cases, while platelet-specific antigens (ie, HPA) may be involved in 10-20% of refractory cases. Combinations of both types of antibodies are seen in approximately 5% of cases. A single random RBC or platelet transfusion induces HLA antibodies in less than 10% of recipients (most likely related to the tolerogenic effect of blood transfusions). However, if patients receive more than 20 transfusions, they become sensitized in increasing proportions. As an example, after 50 transfusions, most patients (as many as 70%) have HLA antibodies. In addition, patients with RBC alloantibodies are more likely to have HLA antibodies.

The presence of HLA antibodies is better correlated with platelet refractoriness than antibodies directed against platelet-specific antigens. In those cases of platelet refractoriness due to HPA antibodies, HPA-1b, HPA-5b, and HPA-1a antibodies are most commonly implicated. The platelet-specific antigen systems are listed in Table 1.

Table 1. Human Platelet-Specific Antigen Systems (Open Table in a new window)

Platelet Antigen System

Protein Antigen

Synonyms

Alleles

Antigen Frequency

HPA-1

GPIIIa

PlA,Zw

HPA-1a = PlA1

HPA-1b = PlA2

97%

26%

HPA-2

GPIb

Ko, Sib

HPA-2A

HPA-2b

99%

14%

HPA-3

GPIIb

Bak, Lek

HPA-3a

HPA-3b

85%

66%

HPA-4

GPIIa

Pen, Yuk

HPA-4a

HPA-4b

>99%

< 1%

HPA-5

GPIa

Br, Hc, Zav

HPA-5a

HPA-5b

99%

20%


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