Lab Testing Of Coag Disorders (Schalm 88)

Question 1

What is the typical blood to citrate ratio for coagulation testing? Under what condition is it occasionally adjusted for some human tests?

Answer 1

1 part citrate (3.2% or 3.8%) to 9 parts blood
May be adjusted for high hematocrit in some human tests

Question 2

What is the trigger reagent for aPTT assays? What factor is first activated with this test?

Answer 2

Phospholipid and negatively charged particles
Factor XII and subsequently prekallikrein; the contact pathway

Question 3

What factor deficiency won’t be noted by prolonged aPTT? What non-factor specific influences is it more susceptible to?

Answer 3

Factor VII
It is more susceptible to platelet count, hematocrit, and plasma protease activity because it lacks exogenous phosphlipid

Question 4

What is the trigger reagent for prothrombin time? Through what factors does it initiate coagulation?

Answer 4

Tissue factor, phospholipids, and calcium
Initiates coagulation through activation of factor VII

Question 5

What test is used to characterize hypofibrinogenemia or dysfibrinogenemia?

Answer 5

Reptilase time
Also thrombin time

Question 6

What substance is a direct activator of factor X? What species is this test particularly useful for?

Answer 6

Russell’s viper venom
Useful in birds to test for vitamin k dependent coagulopathy and avoids the need for avian-source thromboplastin

Question 7

What may result in prolonged thrombin time?

Answer 7

Fibrinogen deficiency or dysfunction
Fibrinogen inhibitors
Presence of heparin and thrombin inhibitory drugs