HOW I DO – Preoperative, Preprocedure Testing – 6
HOW I DO – Preoperative/Preprocedure Tests PART – 6
(All the articles published in past are available at www.shyamhemoncclinic.com/blog/)
Question: In last part, we covered some important points related to transfusion. 1. Leucoreduction importance. Bedside using a filter versus at blood bank prestorage. Later is preferred. Leucoreduction makes febrile reactions rare. Also reduces risk of CMV infection. And risk of antibody formation – this is important for patients requiring long term transfusion support e.g. thalassemia major, MDS, aplastic anemia. 2. Irradiated, or Washed red cells have limited utility in routine medical practice. 3. FFP usual dose is 10-15 ml/kg i.e. 2-4 units for an average adult. Half life of most coagulation factors is around 6-8 hours or less. Hence in most patients, repeated dosing is required at least two to three times a day. 4. For some rare factor deficiencies, FFP is used electively for prevention, with frequency of once every 2-4 weeks. 5. Cryoprecipitates are used for replacement of fibrinogen mainly in DIC; vWF deficiency; Hemophilia A (now mostly factor 8 is used in our region as well). Standard adult dose of cryoprecipitate is at least 6-10 units at one time.
A common hematology issue for many doctors is preoperative testing. And surgical clearance especially when patient has abnormal cbc or coagulation tests, or they are on antiplatelets or anticoagulation. Can you guide us?
Answer: Most certainly. I think you have chosen a very relevant topic for day to day practice. Let us start with a seemingly normal person (no obvious bleeding disorder) due for surgery or procedures like angiography or angioplasty. How much evaluation is required?
Most important evaluation is actually HISTORY. Most basic questions to ask are: any surgery or procedure in past? Any injury requiring stitches? Any dental extraction? If patient did not have unusual bleeding during any one of these, chances are very low for a congenital bleeding disorder. On the other hand, if there is history of unusual bleeding with or without any of these procedures, such as recurrent large ecchymoses/bruises, need for blood products after procedure, prolonged bleeding requiring much longer than usual care or longer hospitalization, or reference to a hematologist etc, then there is a potential bleeding disorder.
Remember that most bleeding disorders are congenital. Acquired are very few e.g. liver disease, which are generally obvious from history or basic blood work up like LFT, Creatinine. List of congenital disorders is very long. Most are suspected based on proper history, aPTT, PT, CBC. But quite a few have normal screening blood work up and yet can cause major bleeding during surgery. These patients are suspected based on good basic history as above.
If history is suggestive of a bleeding disorder, but PT, aPTT, CBC are normal, you still should refer to a hematologist.
On the other hand, if there is history of previous surgery or tooth extraction with no issue, and recent PT, aPTT, CBC are normal, patient is ok. It is extremely unlikely in this case to have a bleeding disorder.
It is important to note here that BT, CT have no role in routine screening preoperatively. Clotting time is essentially a very crude form of aPTT and is unreliable. Most good laboratories don’t even offer this test any more. Bleeding time, the way it is done as part of preoperative work up is of practically no use. Correct BT is done by specialty hematology laboratories only, and that too by very select laboratories. As it requires very specific procedure, with a specified size of skin cut on forearm (not fingertip), with blood pressure maintained at 40 mm Hg using a BP cuff on that arm, and bleeding time is measured.
Also, bleeding time does not correlate with effect of antiplatelet agents well. Hence should not be used for this purpose either. There are plenty of published papers to confirm this fact.
Que: Thank you so much for this clarity. Importance of HISTORY, and no value of BT, CT. How important it is to have PT, aPTT in a good laboratory? And CBC too?
Ans: Yes. Very important. Among common blood tests, PT, aPTT are amongst the most difficult tests. They require daily standardization by using external controls, and high quality reagents and coagulation machine. Otherwise there is a high chance that report will not be accurate. This is precisely the reason why monitoring of patients on warfarin is difficult using PT, for patients who do not have access to a high quality laboratory such as those living far away from major city/town. Unfortunately, many laboratories in peripheral towns and villages, and some even in the cities do not follow strict quality criteria for coagulation tests. We must get into the practice of asking for a very good laboratory and demand quality. In addition, these tests need to be run on comparatively fresh samples. Hence cannot be sent from periphery to main city unlike many tests done from serum. Amount of blood in the tube should also be optimum, e.g. too little blood leads to inappropriate ratio of citrate to plasma. This can give false high coagulation tests. Similarly CBC especially platelet count number and morphology can give clue to a bleeding disorder. Hence you have to alert lab to look for platelet morphology specifically when you are asking for a CBC for this purpose.
December 14th , 2024 Dr Chirag A. Shah; M.D. Oncology/Hematology (USA), 9998084001. Diplomate American Board of Oncology and Hematology. Ahmedabad. drchiragashah@gmail.com www.shyamhemoncclinic.com