Confused, need some clarification. Re: Liver function & coagulation & PT/PTT.

[Knicks]

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I was studying from a source that I'll leave nameless, and I came across a piece of text that confused me.

In a nut-shell, it said that measuring the PT is the most important test when one wants to assess liver function, since all coagulation factors are made in the liver (besides Factor 8); so in liver disease, the PT would increase (which is true).


But shouldn't the PTT be the most important test?, since it follows more of the coagulation factors?

PT <---> Extrinsic <---> we're mainly concerned with Factor 7.

PTT <---> Intrinsic <---> more coagulation factors involved (12, 11, 9 are specific for the intrinsic pathway; that's three extra coagulation factors).


Thanks in advance.

 

[MeRLin443]

So you are right in that both PTT and INR (PT) go up in liver dz, but INR is the best test because it goes up sooner. The reason INR goes up before PTT is because factor VII has the shortest half-life of coagulation factors, so in Vit K deficiency or liver dz VII drops first.

 

[Knicks]

^^ Brilliant.

Thanks a lot!

 

[VCU07]

So you are right in that both PTT and INR (PT) go up in liver dz, but INR is the best test because it goes up sooner. The reason INR goes up before PTT is because factor VII has the shortest half-life of coagulation factors, so in Vit K deficiency or liver dz VII drops first.

I too, was taught that INR is the best measure of liver fx.

 

[werd]

but keep in mind that function has to be pretty bad before any lab abnormalities develop. normal labs don't equal normal liver.

 

[clinicallabguy]

So an INR increases before total bilirubin or unconjugated bilirubin increases?
If so, how much longer before bilirubin is affected?