HIT, OD and SRA

Q: In the diagnosis of Heparin Induced Thrombocytopenia (HIT), Optical-Density (OD) corelates with the probability of Serotonin release assay (SRA) positivity?

 A) True

B) False

Answer: A

SRA is considered as a gold standard for the diagnosis of HIT but is not widely available. At least one large study has shown a good correlation between anti-platelet factor 4 (PF4)/heparin antibodies and SRA. OD signifies the level of titer of antibody in patient's serum.

• OD <0.40 – SRA positive in 0.0-0.1 percent
• OD 0.40 to <1.00 – SRA positive in 1-5 percent
• OD 1.00 to <1.40 – SRA positive in 18-30 percent
• OD 1.40 to <2.00 – SRA positive in 50-58 percent
• OD >2.00 – SRA positive in 89-100 percent

#hematology

References:

1. Warkentin TE, Sheppard JI, Moore JC, et al. Quantitative interpretation of optical density measurements using PF4-dependent enzyme-immunoassays. J Thromb Haemost 2008; 6:1304. 

2. Whitlatch NL, Kong DF, Metjian AD, et al. Validation of the high-dose heparin confirmatory step for the diagnosis of heparin-induced thrombocytopenia. Blood 2010; 116:1761.

3. Baroletti S, Hurwitz S, Conti NA, et al. Thrombosis in suspected heparin-induced thrombocytopenia occurs more often with high antibody levels. Am J Med 2012; 125:44.