title: Validation of whole blood impedance aggregometry as a new diagnostic tool for HIT: results of a large Australian study.
abstract: Heparin-induced thrombocytopenia (HIT) remains a challenge, with diagnosis confirmed only by functional assays. The gold standard 14C-serotonin release assay (SRA) is highly sensitive but technically challenging and unsuitable for routine use. We conducted a large study to validate whole blood impedance aggregometry (WBIA) as a suitable diagnostic tool for HIT. WBIA and SRA were used to test 181 samples positive for H-PF4 antibodies by PaGIA or ELISA. Using the same high responder donor, 77 samples were positive by WBIA (aggregation with low-dose but not high-dose heparin). Using the strict definition for SRA positivity, 72 samples were true HIT. In nine samples, serotonin release with high-dose heparin dropped by > 50% but was still >20%; these were retested after a one-half dilution and 8/9 became positive. Ten other samples were discrepant between the two assays: one strongly positive (89% release) and six weakly positive samples by SRA (average release 56%) were WBIA negative. When these samples were retested using a random donor, only two remained SRA positive. Three samples were strongly WBIA positive but SRA negative; two were retested by SRA with 0.5IU/ml heparin and one became positive. Under controlled conditions, using the same selected high-responder donor, WBIA and SRA performed similarly with slightly increased sensitivity of the WBIA when using the strict definition of SRA positivity. WBIA is easy to perform with rapid turn-around time and warrants a multi-laboratory trial to complete its validation as a confirmatory assay for platelet-activating HIT antibodies.
authors.affiliation: Northern Blood Research Centre, Kolling Institute of Medical Research, University of Sydney, Sydney, Australia. marie-christine.kopp@sydney.edu.au
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Morel-Kopp
authors.forename: Chee Wee
authors.initials: CW
authors.lastname: Tan
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Brighton
authors.forename: Simon
authors.initials: S
authors.lastname: McRae
authors.forename: Ross
authors.initials: R
authors.lastname: Baker
authors.forename: Huyen
authors.initials: H
authors.lastname: Tran
authors.forename: Peter
authors.initials: P
authors.lastname: Mollee
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Kershaw
authors.forename: Joanne
authors.initials: J
authors.lastname: Joseph
authors.forename: Christopher
authors.initials: C
authors.lastname: Ward
mesh_terms: D000328:Adult; D000906:Antibodies / Q000097:blood; D001315:Australia; D003947:Diagnostic Techniques, Radioisotope / Q000706:statistics & numerical data; D003955:Diagnostic Tests, Routine; D017097:Electric Impedance; D005240:Feasibility Studies; D005260:Female; D006403:Hematologic Tests / Q000379:methods; D006493:Heparin / Q000008:administration & dosage / Q000009:adverse effects* / Q000031:analogs & derivatives; D006801:Humans; D008297:Male; D015588:Observer Variation; D010974:Platelet Aggregation; D010978:Platelet Factor 4 / Q000276:immunology; D010979:Platelet Function Tests; D012680:Sensitivity and Specificity; D012701:Serotonin / Q000378:metabolism; D013921:Thrombocytopenia / Q000139:chemically induced / Q000175:diagnosis* / Q000276:immunology
chemical_list: D000906:Antibodies; D012701:Serotonin; D010978:Platelet Factor 4; D006493:Heparin