DIFFERENCE BETWEEN PTT AND APTT

We know ,there are two pathways involved in blood coagulation process ,the intrinsic system and the extrinsic system

Common coagulation pathway is the Intrinsic pathway which is now called as Contact activation pathway

PTT (partial thrombloplastin time) and APTT
(activated partial thromboplastin time) Measures the efficiency of Intrinsic pathway (any deficiency in F2,F5,F8,F9,F11 and F13).whereas the efficiency of extrinsic pathway is measured using PT(prothrombin time)

There is a trick to remember these.

PeT  PiTT bull. (PT-extrinsic and PTT-intrinsic)

What is PTT ?

           It is the time from the activation of factor 12 by silica or phospholipid to the formation of fibrin clot.

Method of checking PTT 

COLLECTION BOTTLE

      Blood is collected in a vaccum tube with oxalate or citrate(to prevent clotting by binding with calcium ion.-------to this, in order to activate intrinsic pathway ,phospholipid is added along with calcium to reverse the effect of oxalate or citrate------then time is measured till clot forms

It is called partial because of absense of tissue factor

                      PTT(normal=30-40sec) is commonly used for patients on heparin therapy.but  its heparin sensitivity is low ,as it is insufficient in detecting minor deficiencies in clotting factors, especially  F8 andF11

                          So in order to cover this,we are now using APTT(normal=25-38sec and in heparin therapy=1.5 to 2 times of normal value,that is60-70sec).Addition of chemicals such as 'contact activators' for example kaolin to the reagent of PTT like silica or phospholipid,which helps to activate F12 rapidly and consistently.Sos APTT is more sensitive to the effects of heparin and so to the deficiencies in F8 andF11 than PTT.

 For a patient with heparin, we measure APTT and for oral anticoyagulants,we use PT values to know the coagulation status

One trick to remember 

Sum of ten

PT+coumadin=10(2 letter+8 letter)

PTT+heparin=10 (3 letter+7letter)