Platelets also known as thrombocytes are an essential component of blood. Platelets have no cell nucleus; they are fragments of cytoplasm derived from the megakaryocytes. Its main function is to clot blood. When there is a deficiency of platelets there are bleeding manifestations. Sometimes they may be fatal like intracranial hemorrhage. Bleeding disorders are broadly classified into 3 categories such as vascular defects, platelet defects, and coagulation defects. There are many reasons for low platelet count. Sometimes platelet transfusion is needed to save lives.

Platelet Disorders

Platelets are fragments of the cytoplasm of the megakaryocyte, hence they are non-nucleated and formed in the bone marrow. The megakaryoblasts are derived from pluripotent stem cells. They can undergo an unusual form of mitosis in which the nucleus, but not the cells, divide. This is called endomitosis, and with each nuclear division, there is a membrane formation and appearance of all the characteristic features of the platelet eg membrane glycoprotein, platelet-specific granules, and lysosomes. The fully mature megakaryocyte can produce as many as 3000 platelets. Morphologically platelets are biconvex discs with a diameter of 2 to 4μm and a volume of 5 to 8fl. Platelet count normally ranges between 150,000 and 450,000/ul of blood. A count below 150,000/μl of blood is generally called thrombocytopenia. Platelets play a significant role in the arrest of bleeding through homeostatic plugs and activation of the intrinsic pathway of coagulation. Their lifespan is about 8-10 days (Average 7 days).

Guideline for Platelet Transfusion

There are many reasons for low platelet count. Sometimes platelet transfusions are needed to save lives.

Non-bleeding patients:

Platelet count <10,000/mm3
Invasive procedure with platelet count < 50000/mm3

Bleeding Patient :

Disseminated intravascular coagulation (DIC) with platelet count < 50000/mm3
Massive transfusion and platelet count <50000/mm3
Active bleeding and platelet count <50,000/mm3
Diffuse bleeding following cardiopulmonary bypass and platelet count not yet available or <100,000/mm3
Platelet function defect, regardless of platelet count.

Indications in Paediatric practice:

Platelet count <10,000/mm 3 without/ low-risk for bleeding.
Platelet count <20,000/mm 3 with hemorrhagic risk factors (infection, organ failure,
clotting abnormalities, minor skin or mucosal bleeding, anemia, GVHD, etc.)
Platelet count 20,000-50,000/mm 3 but the patient has prolonged bleeding like epistaxis, GI
or CNS bleeding.
The patient is scheduled for a major invasive procedure & the platelet count
<50,000/mm 3. (for minor procedures transfusion is considered in <25,000/mm 3 )

Guidelines for platelet transfusion in Neonates

• Platelet count <30,000/cubic mm: Transfuse all neonates even if asymptomatic.
• Platelet count 30,000 to 50,000/cubic mm: Consider transfusion in:
– Clinically unstable
– Newborns <1000 gm and <1 week of age
– Previous major bleeding (IVH grade 3-4)
– Current minor bleeding (petechiae)
– Concurrent coagulopathy
– Requiring surgery or exchange transfusion
– Platelet count falling and likely to fall below 30,000
• Platelet count >50,000 to 99,000/cubic mm: Transfuse only if actively bleeding.

Amount of platelets to be given:

The usual recommended dose of platelets for neonates is 10-20 ml/kg.
The predicted rise in platelet count would be 20 to 60,000 /cubic mm.

When platelets can not be given

Relative Contraindication :

Thrombotic Thrombocytopenic Purpura (TTP)
Heparin-induced thrombocytopenia (HIT)
Idiopathic Thrombocytopenic Purpura (ITP)
Thrombocytopenia associated with Septicemia or in case of Hypersplenism.

Platelet Concentrate Preparation:

From Whole Blood (RDP):

PRP method
Buffy coat method

By Apheresis (SDP):

From Single blood donor

Random donor platelet (RDP):

The volume of 50–60 ml plasma (from a single whole blood donation) should contain:

Platelets : 5.5 x 10^10/l
Red cells : <1.2 x 10^9/l
Leucocytes : <0.12 x 10^9/l

Platelets are prepared from 4 to 6 donor units (‘pooled’ platelets). 1 unit RDP should raise the PLT count by 5 x 109 to 10 x 109 /L. Platelet patients when given 1 unit RDP, they act as SDP transfusion.

Single donor platelet (SDP) / Apheretic Platelet:

A plateletpheresis component is prepared from one donor by the apheresis method.

1 SDP: 1 therapeutic dose
One platelet pheresis should increase the adult patient’s platelet count to 40 x 10^9 – 60 x 10^9/L

Parameters	Amount
Volume	200 – 400 ml
Platelet count	>300 x 109/L
pH	≥ 6.2 (at the end of the labeled storage )
Leucocytes	<5 x 106 (Leuco-reduced)
Red cells	Trace to 0.5 ml

Advantages of SDP over RDP:

Reduction in transfusion frequency
Prevention of alloimmunization
Leuco-reduced platelet
One SDP = one therapeutic dose

Comparison between RDP and SDP

	RDP	SDP
Preparation	By Centrifugation	By apheresis
Volume	50-60 ml	200-400 ml
Platelet count	4.5-5.5 x 10^10/L	3-5 x 10^11/L
Red cell count	Negligible	May be considerable
Leucocyte count	<1.5 x 10^9/L	<.5 x 10^6/L
Risk of Bacterial contamination	High	Low
Risk of Alloimmunization	High	Low
Transfusion frequency	More	Less
Post transfusion increment	Lower	Higher
Cost	Less	High
Main potential risk	Bacterial contamination	Circulatory overload

How to store Platelet concentrate:

Stored at 20°C to 24°C with continuous agitation for 5 days.
Platelets lose their hemostatic function within 24 hours in whole blood when stored at 4°C (lose discoid shape)
Should be transfused within 30 minutes of issuing.

All kinds of blood and blood components are prepared and managed by the Department of Transfusion Medicine at BSMMU.