Although short activated partial thromboplastin times (APTTs) are generally considered to be laboratory artefacts of problematic blood collections, there is mounting evidence that in some cases a short APTT may reflect a hypercoagulable state, potentially associated with increased thrombotic risk and adverse cardiovascular events. We prospectively evaluated the phenomenon of short APTTs in 113 consecutive samples compared with an equal number of age and sex-matched normal APTT samples. We found a significant difference in various test parameters including prothrombin time (PT), Factor (F) V, FVIII, FXI, FXII, von Willebrand factor (VWF) antigen and collagen-binding activity, and in the level of procoagulant phospholipids, as assessed using a novel assay procedure (XACT). Interestingly, there was a significant negative association for fibrinogen, and although elevated, there was no significant association for FIX. On the basis of identified consecutive samples having multiple low APTTs on several sequential days, a proportion of laboratory-defined short APTTs appear to represent in-vivo hypercoagulability. In conclusion, plasma from patients presenting with short APTTs is reflective of a complex hypercoagulant milieu that could feasibly contribute to thrombotic risk, and 20% or more of laboratory definable short APTTs appear to reflect in-vivo phenomenon.

We review the association between disorders of endocrine function and hemostasis. The content of more than 570 review articles were appraised to provide the core of 81 key articles referenced in this chapter. The search method used MEDLINE and EMBASE electronic databases and the key words e NDOCRINE DYSFUNCTION, DIABETES, GRAVES' DISEASE, HYPOTHYROIDISM, HYPERTHYROIDISM, THYROTOXICOSIS, VON WILLEBRAND DISEASE, VON WILLEBRAND FACTOR, BLEEDING DISORDERS, PLATELETS DYSFUNCTION, HEMOSTASIS DYSFUNCTION, and REVIEW. Abnormalities of hemostasis, platelets, and endothelium and the presence of microparticles, abnormal expression of adhesion molecules, and elevated von Willebrand factor are all associated with cardiovascular disease and are also features of various endocrine disorders, including diabetes and its complications, insulin resistance, polycystic ovary syndrome, and various thyroid disorders. Related causes and associated factors, including obesity, alcohol, hyperlipidemia, omega fatty acids, vitamin D, serotonin, insulin-like growth factors, angiotensin-converting enzyme, and C-reactive protein, are also discussed in this review.

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Short activated partial thromboplastin times (APTTs) are associated with thrombosis. However, what short APTTs actually represent in terms of possible mechanistic pathways is not well characterized. We have assessed thrombin generation as compared with levels of procoagulant factor (fibrinogen, V, VIII, IX, XI and XII) activities, von Willebrand factor level and activity using collagen binding, as well as procoagulant phospholipid activity, in 113 consecutive samples exhibiting a short APTT compared with an equal number of age-matched and sex-matched samples yielding a normal APTT. We found a significant difference in peak thrombin generation, velocity index and area under the curve between the two groups, and that thrombin generation markers correlated with the APTT, procoagulant phospholipid activity and several procoagulant clotting factors. We conclude that short APTTs represent a procoagulant milieu, as represented by heightened thrombin generation and several other heightened procoagulant activities, which may help explain the association with thrombosis.

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