Dr.S.Venkatesan MD

What happens to  bleeding time  with   antiplatlet drugs ?

1. Does not have any effect
2. Prolongs  it marginally  .(This can not be detected accurately by the conventional  Ivy  bleeding time)
3. BT is  significantly prolonged at therapeutic doses .Bleeding time is useful to monitor efficacy of these drugs.
4. Prolongs only with loading dose hence it has no clinical  utility .

Answer :

I have been struggling to find an answer in the literature .  Response 2 seems to be  correct .

Back to basics

We are taught reverently  in the first clinical year  at  medical schools ,   platelets are primarily responsible for   stopping  the capillary bleeding . Clot formation follows later . The coagulation cascade occurs over the platelet plug with number of mediators  from platelet  taking part in the clotting process.

If  anti-platelet drugs  functionally  paralyse the platelets ,  it  must  prolong the bleeding time . If that is so ,  why  we  are simply not bothered about measuring bleeding time  to assess the efficacy of anti-platelet drugs ?

Surgeons tell us every other  day about the  ooze in a patients pretreated with aspirin. In fact there is very good evidence for this . Following data is taken from  the journal  “Blood” in 1969 .

There are few  important reasons why bleeding time  is  not in vogue to monitor anti-platelet efficacy

• A marginal elevation (  say  . . .  from 6 minutes to  8 minutes  ) may not convey any  meaning (Is it really  so ?)
• The method of bleeding time measuring is  primitive one ( Ivy ) and it is time-consuming (Since the normal bleeding time can be up to 3-9 minutes   ,it is too long period for the  modern day cardiologist )
• A prick  has  to be made  and the patient  may  feel awkward.(While he can very  well tolerate  the nicks in radials and femorals !)
• Simple BT  costs nothing and can be readily done in bed side , while digital platelet  reactivity testing adds  spice ! It  would be humiliating  for   a  cardiologist  (who lands to the cath lab in  a Audi saloon )  to order for simple bleeding time

So what does the  newer platelet assay tools do ?

Ironically  , the currently available   sophisticated point of care platelet function test is   grossly error prone .Currently they are not recommended  for routine use . So what is the big deal ?  Modern  physicians  has no right to ridicule the  age-old tests ! . In fact  should try to  give a new lease of life  to  the conventional  BT .

I personally feel  there could be a role  for  conventional BT in    an  occasional   patient   after  complex angioplasties . Confirming the  adequacy  of  anti platelet  drug is critical   .  A simple   one time  monitoring of  bleeding time  24-48 hours  after  a PCI  with full dose of anti-platelet  drugs  should help us track and monitor the efficacy  these drugs .  My  guess is  it can be kept  at upper border of normal or slightly above it . If we know the basal  bleeding time it will be added advantage as one can prolong  it  more objectively.

We plan to undertake a simple study of effect of loading dose of clopidogrel  on the  bleeding time . The results will be reported .

Final message.

Ignoring age-old basic medical concepts is  a  serious  threat  facing  the  current   medical professionals . Can we afford to  ignore a  grossly elevated ESR   in a patient with fever , since it is cheap and primitive investigation . Similarly a   low bleeding time   in a patient with  dual anti-platelet therapy   and a drug eluting stent   would  convey a  serious message ,  (All is not well   In  terms of adequacy of platelet inhibition.   ! )

Reference

1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1995097/pdf/nhj1529900.pdf (Point of care instant platelet function testing)
2. http://bloodjournal.hematologylibrary.org/content/34/2/204.full.pdf
3. http://en.wikipedia.org/wiki/Bleeding_time