Improving the specificity of the PF4 ELISA in diagnosing heparin-induced thrombocytopenia.

Heparin induced thrombocytopenia (HIT) is a serious complication of heparin therapy. The PF4 ELISA is a serologic assay that provides laboratory support for the clinical diagnosis of HIT, but it is often positive in patients who do not have the syndrome. We examined whether the specificity of the PF4 ELISA can be improved by 1) taking antibody potency into consideration, 2) by measuring only IgG antibodies, and 3) by utilizing a high concentration heparin inhibition step. We reviewed clinical information on 116 patients whose samples were referred for HIT antibody testing and assigned each a clinical score related to the likelihood of the patient having HIT. The scores were then correlated with serologic findings. Patients with strongly positive PF4ELISA results (OD ≥ 1.0) using both versions of the assay (IgG/A/M and IgG only) had clinical scores and SRA activity that were significantly higher than those having reactive or negative results. When the IgG-only PF4 ELISA was used, only the strongly positive result group had significantly higher clinical scores and SRA release, and fewer samples were classified as weakly positive or reactive, suggesting that detection of IgG only in the PF4 ELISA improves the assay's specificity. The heparin inhibition step identified "reactive" samples that were associated with clinical scores and SRA release indistinguishable from the "negative" result groups, confirming that this step further improves specificity of the test. This study supports utilizing these 3 modifications of the PF4 ELISA to improve specificity in supporting the clinical diagnosis of HIT.

A novel family of mobile genetic elements is limited to the germline genome in Tetrahymena thermophila.

In the ciliated protozoan Tetrahymena thermophila, extensive DNA elimination is associated with differentiation of the somatic macronucleus from the germline micronucleus. This study describes the isolation and complete characterization of Tlr elements, a family of approximately 30 micronuclear DNA sequences that are efficiently eliminated from the developing macronucleus. The data indicate that Tlr elements are comprised of an approximately 22 kb internal region flanked by complex and variable termini. The Tlr internal region is highly conserved among family members and contains 15 open reading frames, some of which resemble genes encoded by transposons and viruses. The Tlr termini appear to be long inverted repeats consisting of (i) a variable region containing multiple direct repeats which differ in number and sequence from element to element and (ii) a conserved terminal 47 bp sequence. Taken together, these results suggest that Tlr elements comprise a novel family of mobile genetic elements that are confined to the Tetrahymena germline genome. Possible mechanisms of developmentally programmed Tlr elimination are discussed.

Neonatal alloimmune thrombocytopenia associated with maternal-fetal incompatibility for blood group B.

BACKGROUND: Blood group A and B antigens are expressed only weakly on platelets (PLTs) of most individuals but are very strongly expressed on PLTs from approximately 1 percent of normal subjects (Type II high expressers). The implications of this trait for transfusion medicine are undefined. STUDY DESIGN AND METHODS: A family was studied in which two Group B infants were born with neonatal thrombocytopenia, whereas a third infant whose blood group was A(2) had a normal PLT count at birth. RESULTS: Serologic studies demonstrated a maternal antibody that reacted strongly with PLTs from the father and the two group B children in flow cytometry and with GPIIb/IIIa from their PLTs in solid-phase assays. No PLT-specific antibodies were detected in maternal serum sample, but it contained a high-titer immunoglobulin G antibody specific for blood group B. All PLT-reactive antibody in the mother's serum was removed by absorption with pooled, washed group A and B red cells (RBCs). Studies with monoclonal anti-B and measurement of serum B-glycosyltransferase activity showed that the father and both group B children were Type II high expressers of blood group B. CONCLUSIONS: The findings indicate that high-titer blood group antibodies acquired from the mother can cause thrombocytopenia in infants possessing the Type II high-expresser phenotype despite competition for antibody binding by blood group antigens expressed on RBCs and other tissues.