Hemato-Oncology-49-Thrombocytopenia spurious myths procedures 3
HEMATO-ONCOLOGY PART-49
(All the articles published in past are available at www.shyamhemoncclinic.com)
Question: Dr. Chiragbhai, thank you for explaining in last part about serious diagnoses leading to thrombocytopenia which must not be missed; importance of good microscope use for diagnosis; when NOT to transfuse platelets; and use of SDP vs RDP.
Ans: Before we go ahead, let me also mention the need to identify false or spurious thrombocytopenia. This can happen in following instances:
1. Platelet clumps – generally due to difficult blood sampling such as thin vein; occasionally aCL antibodies.
2. Satellitism – EDTA associated antibodies which cause platelets to adhere to white cells in tube.
3. Giant platelets – some people, more commonly from India’s eastern states have large platelets, which are not counted by machine, but in peripheral smear they are seen. Many of these patients have mild thrombocytopenia even with manual count.
4. Dilutional – such as collection from a cvp line without stopping iv fluids.
Que: You had mentioned earlier about myths related to thrombocytopenia. Can you clarify?
Ans: Yes. Following are the most common myths:
1. Aspirin causes low platelets = it only causes platelet dysfunction. Number does not reduce.
2. Renal failure leads to low platelets = as above, only dysfunction.
3. LMWH does not cause HITT and can be used in HITT = it can cause HITT, although at lower frequency than unfractionated heparin. Must not be used in HITT as antibodies cross react.
4. Platelets are absolutely contraindicated in ITP or TTP = in both these conditions, platelets have less effectiveness but can be used in patients with major bleeding. However they should not be given to raise platelets in patients without major bleeding.
5. SDP is more effective than RDP in raising platelet count = both are equally effective, but right dose need to be given. One SDP is equal to about 8 RDPs.
Que: That is amazing. Even I was not clear about some of these points. One other practical question is about safe count for performing procedures in patients with low platelets.
Ans: Yes, important question. A number of misconceptions around this lead to unnecessary platelet transfusions or withholding important procedures.
1. <10,000 – bone marrow biopsy, CVP line placement (by an expert – routinely done at our center) 2. 20-50,000 – Lumbar puncture by expert (if expert not available, over 50,000), minor procedures e.g. paracentesis 3. > 50,000 – minor surgery, lymph node biopsy
4. >100,000 – any major surgery, including CABG etc (no need for platelet above 150,000)
Above platelet numbers are not applicable if there is associated coagulopathy i.e. high PT, aPTT or other. Except for ascitic tap (paracentesis) where there is no need to check for coagulopathy.
Que: What other interesting facts can you share with us about platelets?
Ans: Well there are many things. Such as ITP, immune thrombocytopenic purpura, commonest cause of low platelets, is due to destruction of platelets by antibodies. This is what we have been thinking for decades. However some sophisticated laboratory studies in last decade showed that in a sizable number of ITP patients there is actually low production of platelets. This led to the development of a medicine for chronic ITP which actually increases platelet production. This drug is Eltrombopag, a TPO receptor agonist. These are receptors on megakaryocytes, where this drug binds, and stimulates them to produce more platelets.
Romiplostim is another such medicine which works in the same way as above, i.e. a TPO receptor agonist.
So we have two medicines approved for use in ITP, which work by increasing platelet production. What we were always taught was that platelet production is always very good in ITP, but it is the destruction which is problem. So many secrets of nature to find !!!
March 12th 2014.
Dr. Chirag A. Shah; M.D. Oncology/Hematology (USA), 079 26754001. Diplomate American Board of Oncology and Hematology. Ahmedabad. drchiragashah@gmail.com Shyam Hem-Onc Clinic. 402 Galaxy, Near Shivranjani, Opp Jhansi ki Rani BRTS, Ahmedabad. www.shyamhemoncclinic.com