All of the following are true about the activated clotting time ...

[tingc95]

All of the following are true about the activated clotting time (ACT) except:
 
  a. It is useful for monitoring warfarin therapy.
  b. It can be performed in the clinic or at the patient's bedside.
  c. It uses diatomaceous earth as the clot activator.
  d. The clinical laboratory scientist inverts the tube until a clot forms.

Question 2

Low-molecular-weight heparin (LMWH):
 
  a. Is essentially as effective therapeutically as unfractionated heparin (UFH)
  b. Has the same anti-thrombin effect as UFH
  c. Can be monitored using the PTT.
  d. Has a shorter in vivo half-life than UFH

[lauravaras]

Answer to Question 1

ANS: A
The ACT can be used to monitor heparin therapy, not warfarin. Diatomaceous earth is used to activate clot formation, and the clinical laboratory scientist does invert the tube until a clot forms, noting the time needed for this to occur.

Answer to Question 2

ANS: A
LMWH has essentially the same therapeutic efficacy as UFH. Because of its lower molecular weight, it does not have the same bridging effect as UFH, and so the antithrombin effect is reduced (not the same). For this reason, the PTT cannot be used to monitor LMWH; it is not responsive. The chromogenic anti-Xa must be used. LMWH has a longer in vivo half-life than UFH; this is one of the advantages.