=======PT/aPTT abnormalities=======

======Causes======

^  Test result  ^^  Causes of test result pattern  ^
^  PT  ^  aPTT  ^ ::: ^
|  Prolonged  |  Normal  |  **Inherited**  |
| ::: | ::: | Factor VII deficiency |
| ::: | ::: |  **Acquired**  |
| ::: | ::: | Mild vitamin K deficiency |
| ::: | ::: | Liver disease |
| ::: | ::: | Warfarin |
| ::: | ::: | DIC |
|  Normal  |  Prolonged   |  **Inherited**  |
| ::: | ::: | Deficiency of factor VIII, IX, or XI |
| ::: | ::: | Deficiency of factor XII, prekallikrein, or HMW kininogen (not associated with a bleeding diathesis) |
| ::: | ::: | von Willebrand disease (variable) |
| ::: | ::: |  **Acquired**  |
| ::: | ::: | Heparin, dabigatran, argatroban, direct factor Xa inhibitors (variable) |
| ::: | ::: | Acquired inhibitor of factor VIII, IX, XI, or XII |
| ::: | ::: | Acquired von Willebrand syndrome |
| ::: | ::: | Lupus anticoagulant (more likely to be associated with thrombosis than bleeding) |
|  Prolonged  |  Prolonged  |  **Inherited**  |
| ::: | ::: | Deficiency of prothrombin, fibrinogen, factor V, or factor X |
| ::: | ::: | Combined factor deficiencies |
| ::: | ::: |  **Acquired**  |
| ::: | ::: | Liver disease |
| ::: | ::: | DIC |
| ::: | ::: | Severe vitamin K deficiency |
| ::: | ::: | Anticoagulants (supratherapeutic doses of many anticoagulants, combined heparin and warfarin, direct thrombin inhibitors, anticoagulant rodenticide poisoning)* |
| ::: | ::: | Acquired inhibitor of prothrombin, fibrinogen, factor V, or factor X |
| ::: | ::: | Amyloidosis-associated factor X deficiency |

======Anticoagulants======

^  Drug class  ^  Drug  ^  Brand name(s)   ^  PT  ^  aPTT  ^  Anti-factor Xa activity  ^
| Vitamin K antagonists | Warfarin | Jantoven | ↑ | ↑/– * | – |
| ::: | Acenocoumarol | Sintrom | ↑ | ↑/–<sup>*</sup> | – |
| Heparins | Unfractionated heparin | | –<sup>¶</sup> | ↑ | ↑ |
| ::: | LMW heparins \\ Enoxaparin \\ Dalteparin \\ Nadroparin | \\ Lovenox \\ Fragmin \\ Fraxiparine | – | ↑/– | ↑ |
| ::: | Fondaparinux | Arixtra | – | ↑/– | ↑ |
| Direct thrombin inhibitors | Argatroban | Acova | ↑ | ↑ | – |
| ::: | Dabigatran | Pradaxa | ↑/– | ↑ | – |
| Direct factor Xa inhibitors | Rivaroxaban | Xarelto | ↑/– | ↑/– | ↑<sup>Δ</sup> |
| ::: | Apixaban | Eliquis | ↑/– | ↑/– | ↑<sup>Δ</sup> |
| ::: | Edoxaban | Lixiana, Savaysa | | | ↑<sup>Δ</sup> |

* Warfarin has a weak effect on most aPTT reagents. However, warfarin use will increase the sensitivity of the aPTT to heparin effect.

¶ While heparin, LMW heparin, and fondaparinux should, in theory, prolong the PT as indirect thrombin inhibitors, in practice most PT reagents contain heparin-binding chemicals that block any heparin effect below a concentration of 1 unit/mL. Above concentrations of 1 unit/mL, heparin effect on the PT may be observed.

Δ Anti-factor Xa activity testing must be calibrated for the specific anticoagulant; this information should be verified with the clinical laboratory.

In principle, many anticoagulants affect common pathway factors and can prolong both the PT and the aPTT if present at high enough levels. As examples:

  - Warfarin typically prolongs the PT alone, but at high levels warfarin can prolong both tests.
  - Heparin typically prolongs the aPTT alone (because PT reagents contain heparin-binding agents that block heparin effect), but at high levels heparin can prolong both tests.
  - Direct thrombin inhibitors (argatroban, dabigatran) typically prolong both tests, but at low levels dabigatran may not prolong the PT.
  - Direct factor Xa inhibitors (apixaban, edoxaban, rivaroxaban) can prolong the PT and aPTT, although these effects are variable.

======Thrombophilia Testing======

^  Thrombophilic disorder  ^  Clinical settings and anticoagulants  ^^^^
^ ::: ^ Acute thrombosis ^ Heparin therapy ^ Warfarin ^ Direct oral anticoagulants ^
| Factor V Leiden | Unchanged | Unchanged | Unchanged | Unchanged |
| Prothrombin G20210A | Unchanged | Unchanged | Unchanged | Unchanged |
| Protein C (PC) deficiency | Unchanged | Unchanged | Cannot measure | Cannot measure using functional assays |
| Protein S (PS) deficiency | Can be lowered | Unchanged | Cannot measure | Cannot measure using functional assays |
| Antithrombin (AT) deficiency | Can be lowered | Lowered | Unchanged | Cannot measure using functional assays |
| Antiphospholipid antibodies | Unchanged | Unchanged | Unchanged | Unchanged |
| Lupus anticoagulant | Unchanged | Cannot measure | False positives possible | Cannot measure |
| Increased factor VIII activity | Acute phase reactant. Do not test while inflammation is still present. ||||
^  Acquired AT deficiency  ^^^^^
| Neonatal period; pregnancy; liver disease; DIC; nephrotic syndrome; major surgery; acute thrombosis; treatment with L-asparaginase, heparin, or estrogens |||||
^  Acquired protein C deficiency  ^^^^^
| Neonatal period; liver disease; vitamin K deficiency; DIC, chemotherapy with cyclophosphamide, methotrexate, and 5-fluorouracil; inflammation; treatment with warfarin or L-asparaginase |||||
^  Acquired protein S deficiency  ^^^^^
| Neonatal period; pregnancy; liver disease; vitamin K deficiency; DIC; treatment with warfarin, L-asparaginase, or estrogens |||||

=====Hepatic Synthesis=====

  * Factor I (fibrinogen)
  * Factor II (prothrombin)
  * Factor V
  * Factor VII
  * Factor IX
  * Factor X
  * Factor XII
  * Factor XIII