Partial Thromboplastin Time (PTT)

PTT (partial thromboplastin time) is a control parameter of blood clotting. The name PTT is actually obsolete because today the test is performed with the addition of a contact activator, in contrast to an earlier variant. The current designation is therefore activated partial thromboplastin time (aPTT). As a so-called global test of plasmatic blood coagulation, it detects several reaction steps of blood coagulation including the binding ability of coagulation factors to phospholipid surfaces. The determination of aPTT is done to monitor therapy with heparin or to detect various congenital or acquired coagulation disorders (clotting disorders).

The procedure

Material Needed

  • Citrate blood

Preparation of the patient

  • Not known

Disruptive factors

  • None known

PTT

Value Meaning
20-38 sec Normal blood clotting
< 20 sec
> 38 sec
  • Hemophilia (hemophilia) – deficiency of factor VIII.
  • Congenital coagulation disorders – deficiency of coagulation factors IX, XI or XII.
  • Consumptive coagulopathy – consumption of clotting factors and platelets/platelets that can lead to a bleeding tendency.
  • Neonatal
  • Heparin therapy
  • Vitamin K deficiency
  • Lupus anticoagulant (antiphospholipid antibody; factor present in about a quarter of patients with systemic lupus erythematosus (SLE)

Indications

  • Detection of hereditary (congenital) or acquired coagulation factor defects.
  • Monitoring of therapy with unfractionated heparin.
  • Clarification of a lupus anticoagulant (antiphospholipid antibody).
  • Preoperative screening for coagulopathy.

Interpretation

See above table. * When anticoagulant therapy with heparin is used, aim for a PTT that is prolonged 1.5-2-fold.

Differential diagnosis of Quick value and PTT

Constellation Interpretation
Quick value decreased, PTT in normal range Suspected diagnoses:

  • Isolated reduction in factor VII activity.
  • Isolated slight decrease in factor V and X activity.
Quick value decreased, PTT prolonged, bleeding symptoms. Overdose of unfractionated heparin must be ruled out first! Suspected diagnoses:

  • Isolated factor deficiency states
  • Reduced synthesis capacity of the liver* .
  • Vitamin K deficiency
  • Consumptive coagulopathy (disseminated intravascular coagulation; see clinical situation).

* Liver synthesis disorders are more likely to be indicated by the Quick test than by the PTT.
Quick value in normal range, PTT prolonged, bleeding symptoms. Suspected diagnoses:

  • Hemophilia A (reduction in factor VIII activity).
  • Hemophilia B (decrease in factor IX activity).
  • Von Willebrand disease (moderately decreased factor VIII activity).