Platelets

Platelet transfusions are indicated for the prevention and treatment of haemorrhage in patients with thrombocytopenia or platelet function defects. Platelets for transfusion can be prepared by centrifuging a whole blood donation or collected by the process of plateletpheresis (platelet component donation). In this book the component is termed ‘platelet concentrate’. Platelets prepared by each method have similar efficacy, but use of apheresis platelets exposes the recipient to the blood of fewer donors. Currently platelet concentrates contain a substantial volume of plasma, required to maintain platelet function during storage, although the use of platelet additive solutions allows the amount of plasma to be reduced. Platelet function is best maintained by storage at 22°C with agitation. As this temperature favours growth of some bacteria, culture of platelet concentrates prior to release from storage is being introduced to reduce the small risk of a unit being contaminated with bacteria.

The usual dose unit for an adult is referred to as an ‘adult dose unit’. It should contain 2.5−3 x 10¹¹ platelets. In practice the dose is often defined in terms of the number of whole blood donations (typically four to six) that are pooled to provide the dose. Alternatively a single plateletpheresis procedure can provide an adult dose unit from a single donor.

Pathogen-reduced platelets

Platelet concentrates can be treated to reduce or inactivate microbial infectivity (not vCJD). Clinical trials have indicated that the product is efficacious. This process has not yet been introduced in the UK. A similar process has been developed for red cells, but the product has encountered problems during clinical trials.

Table 3 Platelets

From whole blood donations: platelets from 4 or 5 donations constitute an adult therapeutic dose (ATD) From apheresis: 1 donor collection provides 1 to 3 ATDs
From whole blood	mean	sd	95% CI	range
Number of donors	4
Volume ml	310	± 33	317−321	250−400
Platelets x 10⁹ (at least 240 x 10⁹)	330	± 50	329−332	180−400
Plasma ml	250
Anticoagulant ml	60
White cells per unit	0.3 x 10⁶ per pack
From apheresis	mean	sd	95% CI	range
Number of donors	1
Volume ml	215	± 53	206−207	180−300
Platelets x 10⁹	290	± 45	289−291	180−400
Plasma ml	180
Anticoagulant ml	35
White cells per unit	0.3 x 10⁶per pack
Storage	5 days at 22 ± 2°C on a special agitator rack (may be extended to 7 days if system is validated and in conjunction with bacterial testing)
Compatibility requirement	Preferably ABO and RhD identical with patient
Dosing guide	For a 70 kg adult, 1 ATD typically gives an immediate rise in platelet count of 20−40 x 10⁹ ml
Administration	Infuse through a standard blood administration set or a platelet infusion set − use a fresh set when administering each infusion of platelets
Cautions	RhD negative females with potential for childbearing must be given RhD negative platelets to avoid risk of Rh sensitisation (see RhD antigen and antibody) Plasma in the platelets can cause an ABO incompatibility reaction (see ABO blood groups and antibodies), TRALI (see TRALI) or allergic reaction (see Allergic reactions)
Source: NBS and SNBTS routine QA data

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