Thrombocytopenia & Platelet Transfusions

1) Approach to Thrombocytopenia:

First, want to rule out pseudothrombocytopenia - an artifact from inadequate anticoagulation of the blood sample; also, 0.1% of the population has EDTA-dependent agglutinins (EDTA is the anticoagulant routinely used for CBCs) --> leads to platelet clumping.  So, look at manual smear, and if clumping, use another anticoagulant (sodium citrate).

 

 

Main categories of thrombocytopenia are increased destruction, decreased production, or abnormal distribution.

 

1.  Decreased production:
a) Hypocellular or Dysfunctional Marrow:  Chemotherapy/XRT, Viruses (Hep C, HIV, Parvovirus, EBV), Aplastic anemia, Myelodysplastic syndrome, Alcohol, Vitamin B12/Folate deficiency, Pure megakaryocyte aplasia
b) Marrow replacement - Leukemia/Lymphoma infiltration, Myelofibrosis

 

2.  Increased destruction:
a) Microangiopathic Hemolytic Anemias (MAHA): DIC, TTP/HUS, HELLP syndrome - see Ellen Eaton's recent MR summary for more
b) Immune-mediated: ITP, Heparin-induced thrombocytopenia, Drug-induced thrombocytopenia, Post-infectious, HIV, other autoimmune (lupus, antiphospholipid syndrome)

 

3.  Abnormal distribution:
a) Splenic Sequestration - from cirrhosis/portal HTN
b) Dilutional Thrombocytopenia - from massive PRBC transfusions (without platelets)

 

Looking at the list above, priorities should be to rule out immediately life-threatening causes of thrombocytopenia; namely the MAHAs (DIC, TTP/HUS, HELLP).

 

The first steps in workup should be:
1. Look at the rest of the CBC, and the smear --> If you have pancytopenia, more likely to be category 1 of decreased production (marrow issues), but still could be other things as well.  On smear, look for schistocytes (for MAHA) first and foremost, but also blasts (for leukemia), platelet clumps as described above for pseudothrombocytopenia, hypersegmented PMNs, etc.  Also check coags to evaluate for possible DIC.
2.  Find out all recent medications, including OTC supplements - basically, any drug can cause thrombocytopenia.  Especially look out for heparin for HIT.
3.  In women, rule out pregnancy --> this is because obstetric issues can lead to several of the catastrophic entities listed above: DIC, TTP, HELLP.  If pregnant, be even more worried! (this is probably a safe general rule of thumb anyways)

 

 

2) Basics of Platelet Transfusions:

Indications for transfusions:

• Platelet count < 10 k for anyone - due to risk of spontaneous bleeding
• Platelet count < 50 k and active bleeding, or major surgical procedure
• ? Serious Bleeding with any platelet count and on antiplatelet agents (ASA, Plavix) --> some evidence that platelet transfusions are helpful, as the patient's existing platelets are not really functional when on those meds

 

Six-pack of platelets vs Single Donor Apheresis

• The older method was to collect a unit of whole blood from a donor and separate out that into 1 unit PRBC, 1 platelets, 1 plasma.  6 such units would be combined to make a "6-pack" of platelets that we are familiar with.
• Newer method, used both at the VA and Stanford, involves Single Donor Apheresis - one "superdonor" is hooked up to a pheresis machine, which basically separates out the platelets only and concentrates them, and returns the other blood components to the donor.  The amount of platelets in a 6-pack and single donor apheresis unit are roughly equivalent and should raise the plt count by ~30k.  So, do not try to transfuse six single donor apheresis units. 
• Benefit to single donor apheresis is that 1) You don't suck the donors dry, and 2) You limit exposure to different donors for the transfused recipient, which can help prevent alloimmunization, and 3) Products are leukoreduced, leading to less risk of transfusion reactions.  

 

(Chanu Rhee MD, 8/31/10)