Diagnostic utility of light transmission platelet aggregometry: results from a prospective study of individuals referred for bleeding disorder assessments

Abstract

Summary. Background: Light transmission aggregometry (LTA) is commonly performed to assess individuals for bleeding disorders. Objectives: The goal was to evaluate the incidence and spectrum of platelet function abnormalities in a prospective cohort of individuals referred for bleeding disorder assessments after exclusion of thrombocytopenia and von Willebrand disease. Patients/methods: Subjects were healthy controls and patients from a prospective cohort of individuals referred for bleeding disorder assessments after exclusion of thrombocytopenia and von Willebrand disease. LTA was performed by standardized methods using platelet-rich plasma adjusted to 250 · 10 9 platelets L )1. Maximal aggregation data were analyzed to determine the likelihood of detecting a platelet function disorder by LTA, and the sensitivity and specificity of LTA for platelet disorders. Results: The incidence of false positive LTA among subjects excluded of having bleeding disorders was similar to healthy controls. Abnormal LTA was more common in subjects with bleeding disorders and the likelihood of a bleeding disorder was significantly increased (odds ratio 32) when maximal aggregation was reduced with two or more agonists. Receiver operator curve analyses indicated that LTA had high specificity and moderate sensitivity for detecting inherited defects in platelet function and that the LTA agonists 1.25 lg mL )1 collagen, 6 lM epinephrine, 1.6 mM arachidonic acid and 1.0 lM thromboxane analogue U44619 detected most inherited disorders with abnormal LTA. Conclusions: LTA is valuable for detecting platelet function abnormalities among individuals referred for bleeding problems, particularly when the test indicates abnormal responses to multiple agonists.

96-well plate-based aggregometry

“…It provides a way to measure platelet function in patients with bleeding disorders (4) and also to assess the efficacy of anti-platelet therapies (5). In addition, the two phases of platelet aggregation (a primary activation and secondary potentiation) as well as disaggregation can be visualized in real time, which are critical in understanding the effects of antagonists or weak agonists.…”

New developments in laboratory diagnosis and monitoring

“…Presently, the most common type of diagnostic assay used to investigate a known or suspected platelet function disorder is an assessment of platelet aggregation function, often by LTA [12,16,17]. Although some laboratories perform Ôscreening testsÕ [such as the bleeding time and Platelet Function Analyzer-100 Ò (Siemens/Dade-behing, Marburg, Germany) closure time] [19], neither the bleeding time nor the closure time has sufficient sensitivity to rule out common platelet function disorders [23,25]. LTA has considerable diagnostic utility when performed by rigorously standardized procedures [25,26] with validated reference intervals [27] on samples from individuals referred for bleeding problems.…”

“…Aggregation responses indicate a single agonist abnormality which is nondiagnostic and could represent a false positive Repeat aggregation testing Platelet ATP release and/or electron microscopy for dense granule deficiency have focused on LTA, and the diagnosis of dense granule deficiency is because standardized LTA and standardized assays for dense granule deficiency, when performed in accordance with guidelines, have important diagnostic utility for the assessment of common bleeding problems [25]. If a higher level of platelet function test standardization can be achieved, it would probably improve the diagnostic evaluation of platelet function disorders worldwide [12].…”

“…more highly predictive of a bleeding disorder than a single agonist abnormality [25]. In Canada, the Ontario Quality Management Program -Laboratory Services recently released consensus recommendations to guide performance of platelet function tests in diagnostic laboratories to promote best and standardized practices in assay performance and also to provide guidelines on LTA interpretation (Table 2) [21] which was not covered by Clinical and Laboratory Standards Institute (CLSI) guidelines [22].…”

“…Although some laboratories perform Ôscreening testsÕ [such as the bleeding time and Platelet Function Analyzer-100 Ò (Siemens/Dade-behing, Marburg, Germany) closure time] [19], neither the bleeding time nor the closure time has sufficient sensitivity to rule out common platelet function disorders [23,25]. LTA has considerable diagnostic utility when performed by rigorously standardized procedures [25,26] with validated reference intervals [27] on samples from individuals referred for bleeding problems. Laboratories need to consider the potential for false positives, as LTA abnormalities with two or more agonists are much …”