External quality assessment of platelet disorder investigations: results of international surveys on diagnostic tests for dense granule deficiency and platelet aggregometry interpretation.

The quality of platelet aggregation and dense granule deficiency testing is important for diagnosing platelet function disorders. After a successful pilot exercise on diagnosing platelet dense granule deficiency by electron microscopy (EM), the North American Specialized Coagulation Laboratory Association (NASCOLA) has launched regular external quality assurance (EQA) for dense granule EM, as well as for the interpretation of platelet aggregation findings. EQA records were analyzed to assess performance. For EM EQA, between 2009 and 2011, there was excellent performance in distinguishing normal from dense granule-deficient samples and good (>70%) agreement on classifying most electron dense structures in platelets. For aggregation EQA, some normal variants were misclassified and overall case interpretations were more acceptable for rare disorders than for common findings. NASCOLA experiences with these EQAs indicate that there is a need to improve the quality of platelet disorder evaluations. For aggregometry interpretations, deficits in performance could be addressed by translating guideline recommendations into practice.

Results of an external proficiency testing exercise on platelet dense-granule deficiency testing by whole mount electron microscopy.

Performance on specialized diagnostic tests for platelet disorders, including dense-granule deficiency, is rarely evaluated by external quality assessment (EQA). Members of the North American Specialized Coagulation Laboratory Association that evaluate platelet dense-granule deficiency commonly use whole-mount electron microscopy (EM) methods. This observation led us to develop a pilot EQA survey with standardized EM images and clinical samples on grids from a healthy control subject and a subject with dense-granule deficiency. The survey participants were 8 centers, including 2 with no experience in platelet whole mount EM. All participants, including inexperienced sites, correctly interpreted findings for the normal and dense-granule-deficient platelets. Among experienced sites, agreement was excellent (>82%) on platelet structures to count or not count as dense granules. Participants indicated that future EQA challenges should include clinical samples on grids and standardized images. This is the first report that platelet EM can be assessed by EQA.

Turnover and fate of fibrinogen and platelets at the rabbit aorta wall immediately after a balloon de-endothelializing injury in vivo.

A de-endothelializing injury to the artery wall in vivo results in a rapid procoagulant response at the surface of the exposed subendothelium. Activated tissue factor (TF)-bearing cells and hemostasis factors located at the site of injury respond by producing thrombin, and within minutes the principal thrombus-forming, blood-borne components (platelets, fibrinogen) accumulate at the site. To compare their behaviors, the rates of uptake and turnover of rabbit (51)Cr-platelets and rabbit (125)I-fibrinogen were quantified simultaneously during the initial 100-min interval after a balloon catheter injury to the rabbit aorta in vivo. Platelets ( approximately 70,000/mm(2)) and fibrin(ogen) ( approximately 2.8 pmol/cm(2)) saturated the ballooned aorta surface within five minutes after injury. Whereas the adherent platelet and fibrinogen concentrations remained steady at the aorta surface, fibrin(ogen)-related products continued to accumulate slowly in the tunica media (TM) for at least 100 minutes. A relatively small proportion (3.7%/min) of adhered platelets turned over at the ballooned aorta surface at 10 minutes, decreasing to 1.2%/min at 100 minutes. By contrast, a larger proportion of fibrin(ogen) ( approximately 20%/min) was turned over within the platelet layer at 10 minutes, decreasing to 6%/min at 100 minutes. As verified by immunostaining aorta sections and by protein analysis of TM extracts, the uptakes of platelets and fibrinogen at the site of injury contributed to an accumulation of products of platelet releasate and fibrin(ogen) degradation (FDPs) within the TM. These observations improve our understanding of the hemostatic processes and subsequent events that occur after an arterial injury in vivo.