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A Practical Guide to Haemostasis


Screening Tests: Summary

Introduction

The following table provides a summary of the results obtained using the PT, APTT, Fibrinogen and Thrombin Time in various disorders.



Platelet Count PT APTT TT Fibrinogen Interpretation
Normal

Normal

Normal

Normal

Normal

Normal profile
Factor XIII deficiency
Mild VWD
Qualitative platelet disorder
Connective tissue problem e.g. Ehlers Danlos
Mild coagulation factor deficiency
Normal

Normal

Normal

Normal

FVII deficiency
Normal

Normal

Normal

Normal

FVIII, FIX, FXI or FXII deficiency
VWD - if the FVIII level is reduced
Lupus anticoagulant - occasionally a very strong lupus anticoagulant or a lupus anticoagulant that has anti-Prothrombin [Anti-II] activity can result in a prolonged PT. Similarly a lupus anticoagulant can also be associated with thrombocytopaenia.]
Other contact factor deficiency e.g. HMWK, Pre-Kallakrein
Normal

Normal

Normal

'Common pathway' deficiency i.e. FII, FV or FX deficiency
Multiple clotting factor deficiencies e.g. combined FV and FVIII deficiency
Warfarin or vitamin K antagonist
Vitamin K deficiency or a mutation within one of the genes encoding key enzymes involved in VK metabolism.
Occasionally a very strong Lupus anticoagulant can cause these findings but it is unusual to see a prolongation of the PT with a LA due to the high concentration of PL used in the PT test.

DIC
Massive transfusion
Liver disease

Normal

Normal

Normal

Normal

Primary platelet problem e.g. ITP.
The Mean Platelet Volume [MPV] can be helpful in establishing the causes of thrombocytopaenia.
A raised MPV is often associated with increased peripheral destruction e.g. ITP - whereas a reduced MPV is often seen in association with bone marrow failure.
A raised MPV can also be found in a number of inherited qualitative platelet disorders.
Changes in the MPV are also seen in patients with various inherited platelet disorders e.g. Wiskott Aldrich syndrome in which the MPV is significantly decreased.

 

The two diagrams below summarise the investigation of a prolonged PT or APTT...

Investigation of a Prolonged PT



Investigation of a prolonged APTT



Anticoagulants and their Effects on Haemostatic Screening Tests 

The following table summarises the results of screening tests in patients who may be taking an anticoagulant.
See also the section on Direct Oral Anticoagulants [DOACs] under 'Useful Information' for further information on the effects of anticoagulants including the DOACs on a number of clotting tests.

Drug PT APTT TT Fibrinogen Comments
Warfarin and similar Vitamin K antagonists

↑/N

No significant effect
No effect

The APTT may be prolonged in patients whose INR on Warfarin is significantly prolonged
Unfractionated Heparin

No effect
 
Low Molecular Weight Heparin

No effect
No effect

May be prolonged

No effect
 
Dabigatran

↑ - test has low sensitivity and results vary with thromboplastin used in the test

↑ in a curvilinear manner but vary with reagents used in the test

No effect or factiously low A normal TT excludes significant Dabigatran levels
Apixaban

No significant effect No significant effect
Edoxaban

No significant effect

No significant effect
 
Rivaroxaban

↑ - results vary with thromboplastin used in the test
  No significant effect No significant effect  
Fondaparinux No effect No clinically significant effect No significant effect No significant effect