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Febrile non-hemolytic transfusion reaction (FNHTR) is the most common type of transfusion reaction. It is a benign occurrence with symptoms that include fever but not directly related with hemolysis. [1] It is caused by cytokine release from leukocytes within the donor product as a consequence of white blood cell breakdown.
If the platelet count is not known then assisted forms of delivery, for example forceps or ventouse, should be avoided to reduce the risk of harm. [19] If the delivery has been planned then antigen negative platelets should be available in case the infant's platelet count is low on a cord blood sample.
One common definition of thrombocytopenia requiring emergency treatment is a platelet count below 50,000/μL. [5] Thrombocytopenia can be contrasted with the conditions associated with an abnormally high level of platelets in the blood – thrombocythemia (when the cause is unknown), and thrombocytosis (when the cause is known). [6] [7]
For example, a PI of 25,000 platelets/μL, a BSA of 1.8m 2 and a PD of 4x10 11 gives a CCI of 11,250 platelets*m 2 /10 11 μL At 1 hour post-transfusion a CCI greater than 7500 indicates a sufficient post-transfusion increment, whereas a CCI less than 7500 is considered diagnostic of platelet refractoriness. [ 10 ]
Higher platelet transfusion thresholds have been used in premature neonates, but this has been based on limited evidence. [19] There is now evidence that using a high platelet count threshold (50 x 10 9 /L) increases the risk of death or bleeding compared to a lower platelet count threshold (25 x 10 9 /L) in premature neonates. [20]
In a typical set of rules, a platelet donor must weigh at least 50 kg (110 lb) and have a platelet count of at least 150 x 10 9 /L (150,000 platelets per mm³). [2] One unit has greater than 3×10 11 platelets. Therefore, it takes 2 liters of blood having a platelet count of 150,000/mm³ to produce one unit of platelets.
A pseudothrombocytopenia false-positive result may occur when automated platelet counting devices are used. As a means of double checking the results, the patient's blood sample is often examined under a microscope. If the clumping is visible and the number of platelets appears normal, pseudothrombocytopenia may be concluded.
This results in platelet activation and the formation of platelet microparticles, which initiate the formation of blood clots; the platelet count falls as a result, leading to thrombocytopenia. [1] [7] In addition, the reticuloendothelial system (mostly the spleen) removes the antibody-coated platelets, further contributing to the thrombocytopenia.