[HouseWannabe]

A 60-year-old man with recurrent bacterial sepsis is hospitalized in order to receive intravenous antibiotics. He is started on his fourth course of broad-spectrum antibiotics within the past month. Three days into the admission, his nurse notes that his venous access is oozing blood. Laboratory tests reveal a prolonged prothrombin time, a prolonged partial thromboplastin time, and a normal platelet count. Which of the following coagulation cofactors would be deficient first in this patient?


A. Factor II
B. Factor V
C. Factor VII
D. Factor VIII
E. Factor XI
F. Factor XII

 

[ath.pantelis]

Such rigorous and repetitive administration of antibiotics would definitely affect this patients normal intestinal flora, provoking a defect in the production of vitamin K.

Vitamin K is necessary for the production of factors II, VII, IX & X. So, the correct answer lies between options A & C.

Now, should factor VII have been affected, there would be disruption of PT only. This pt's abnormal PT & PTT indicates a defect in a factor of the common pathway, which makes factor II (choice A) the only correct answer among the available options.

 

[ashishkabir]

i find this one a little confusing - I'm thinking Factors II and VII but i can't choose between them...

 

[ath.pantelis]

Btw, I have made a mnemonic concerning the relation EXtrinsic pathway - PT prolongation - factors VII & III:

EX-PaTriot fought in the conflict of '73. (1973 is a paramount year in my homeland, hope at least it helps my fellow Greek students!)

 

[ashishkabir]

That makes much more sense! Thanks ath.pantelis...

multiple step reasoning... I need to grasp the material as well as you do. thanks for the help!

 

[Seetal]

ahh... makes sense

i was leaning towards factors II and V because they are common in both PT and PTT pathways. but after seeing how that it is related to a def in Vit. K, i see how factor II is the answer.

thanks dr.ath.pantelis. EXPT73!!

 

[HouseWannabe]

Such rigorous and repetitive administration of antibiotics would definitely affect this patients normal intestinal flora, provoking a defect in the production of vitamin K.

Vitamin K is necessary for the production of factors II, VII, IX & X. So, the correct answer lies between options A & C.

Now, should factor VII have been affected, there would be disruption of PT only. This pt's abnormal PT & PTT indicates a defect in a factor of the common pathway, which makes factor II (choice A) the only correct answer among the available options.

You're reasoning is excellent; however, you need to look at this in the simplest way possible the only factor that has the shortest half-life is factor VII.

 

[HouseWannabe]

Correct Answer: C

The correct answer is C. Vitamin K is synthesized by the intestinal flora; therefore long-term treatment with broad-spectrum antibiotics can induce a vitamin K deficiency by clearing intestinal flora. Vitamin K is a necessary cofactor for hepatic production of clotting factors II, VII, IX, and X and proteins C and S. Factor VII has the shortest half-life of all clotting factors (4-6 hours), which is why the prothrombin time is prolonged first in vitamin K deficiency.

Answer A is not correct. Factor II requires vitamin K as a cofactor, and early factor II deficiency would result in prolongation of prothrombin time and partial thromboplastin time. However, the half-life of factor II is 42-72 hours, and thus it would not be deficient before factor VII is deficient.

Answer B is not correct. Vitamin K is not required for factor V synthesis and would not be deficient in this patient.

Answer D is not correct. Factor VIII is not a vitamin K dependent clotting factor.

Answer E is not correct. Factor XI is not a vitamin K dependent clotting factor.

Answer F is not correct. Factor XII is not a vitamin K dependent clotting factor.

 

[ath.pantelis]

...and elevated PTT is due to the other factors affected?

Ok, got it... I'm losing it... I'll stop posting for a while, until I find myself back!

 

[Seetal]

...and elevated PTT is due to the other factors affected?

Ok, got it... I'm losing it... I'll stop posting for a while, until I find myself back!

no dont stop posting. u learnt best from yr mistakes. if u only want to learn from being right, there wont be much learning.