Summary:Abnormalities that have been reported for platelet indices and function, coagulation factors and tests, and the fibrinolytic system in hypothyroidism are reviewed. These abnormalities, although usually of limited importance clinically, may occasionally lead to major bleeding episodes and to diagnostic confusion.

To improve the appropriateness of blood-component prescribing, a mandatory haematologist pretransfusion approval programme of all non-red-cell components was instituted. This was associated with a 33% decrease in the units of fresh frozen plama (FFP) transfused. Platelet transfusions increased but utilization of both platelets and FFP are now the lowest of the six comparable blood transfusion regions in New Zealand. A subsequent concurrent audit, using preset criteria, of FFP, cryoprecipitate and platelet usage over a 3-month period showed that further reductions in blood component usage could still be achieved, despite the continuing pretransfusion approval policy. This audit showed that 33% of FFP and 30% of cryoprecipitate units transfused were inappropriately given, despite prior haematologist approval. Hospital transfusion practices can be improved by mandatory blood-component pretransfusion approval but concurrent auditing of this programme is required to identify and correct continuing inappropriate blood-component prescribing. Haematologists need to agree on blood-component indications prior to instituting a pretransfusion approval programme in order to provide optimal management.

In 28 unselected patients with hyperthyroidism, platelet count, platelet hematocrit, mean platelet volume, and platelet distribution width were measured at the time of presentation and again when the patients were euthyroid. On return to the euthyroid state, there were highly significant falls in the mean values of the mean platelet volume (16% decline, P less than 0.001) and the platelet hematocrit (16% decline, P less than 0.001) and a slight but highly significant increase in the mean value of the platelet distribution width (2% increase, P less than 0.01). A decline in mean platelet volume was observed in 24 of 28 patients (86%); three patients showed no change. There was no significant change in the mean value of the platelet count. The observed effects of thyrotoxicosis on platelets appeared to be largely independent of the well-known effects on erythrocytes and white blood cells. An increase in mean platelet volume is a regular feature of hyperthyroidism that has not previously been described.

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare acquired haemolytic anaemia. Cardiac bypass surgery in patients with PNH may be complicated by aggravation of haemolysis in addition to increased risk of infection, renal failure, bleeding and thrombosis. We describe a case of uncomplicated cardiopulmonary bypass surgery for aortic valve replacement and aortoplasty in a patient with PNH and discuss some recommendations to reduce the risk of peri-operative complications.

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