Coagulation

The BCPS offers a range of routine and specialised coagulation testing, including factor assays, vWF activity and antigen and thrombophilia testing (including in house prothrombin gene mutation and factor V Leiden testing).

All sites within the BCPS can perform routine coagulation testing with specialised testing centralised at the hub site. Refer to the table below:

Each of the haematology laboratories across the BCPS utalise Werfen TOP analysers. The Hub also has an additional immunoassay analyser for some of the specialist coagulation testing.

Hub: 2 x ACL TOP 550s + ACL Acustar Immunoassay.

ESLs: 2 x ACL TOP 350s

Coagulation sample collection information

For all specialised coagulation tests, three citrate tubes are required (although other sample types may be required) – please see test directory for specific tests. For difficult to bleed patients and paediatric patients 1ml citrate sample tubes are available.

Please ensure that there is no possibility of contamination of sample with heparin or other IV fluids – e.g. flushed from venflons etc.

Please collect coagulation samples before all other sample types with a minimum of stasis or delay. Do not top up coagulation tubes from other samples.

Please ensure each tube is correctly filled – under or over-filled samples give unreliable results and will not be tested.

All coagulation samples must be received and assayed within six hours of collection.

All specialist coagulation tests are vetted prior to testing to ensure that the tests requested are relevant. Please ensure that relevant clinical information is included in the clinical details to help ensure that the samples are processed and not delayed. Please also include in the clinical details any current anticoagulation. For any urgent specialised coagulation testing, please contact the laboratory directly. For any further help and advice, please contact the on-call haematologist through the various hospital switch boards.

General guidance for interpretation of Routine coagulation test

Raised INR

• Patient taking oral anticoagulants.
• Consider acquired coagulation disorder e.g. Liver disease, DIC.
• Consider hereditary coagulation disorder (rare).

Raised APTT ratio

• Patient on unfractionated heparin.
• Consider Acquired coagulation disorder e.g. Liver Disease, DIC
• Consider Hereditary coagulation disorder e.g. haemophilia (FVIII deficiency), Christmas disease (FIX deficiency), von Willebrands Disease, Lupus inhibitor.

D-Dimer advice

D-Dimer is a useful diagnostic test as a negative predictor for deep vein thrombosis (DVT) and pulmonary embolus (PE). It can be used when these conditions are suspected to prevent unnecessary anticoagulant therapy and invasive diagnostic tests.

The D-Dimer should only be used when the pre-test probability score (Wells score) is low.

However, many clinical states are associated with an elevated D-Dimer level and so in the following situations the D-Dimer is of no value:

• Pregnancy
• Post-natal
• Post-operative
• Post-trauma
• Myocardial infarction
• Peripheral arterial disease
• Thrombolytic therapy
• Malignancy including leukaemia.
• Sickle cell crisis
• Newborn infants
• Liver and renal disease
• Gram-negative bacteraemia

Anticoagulant therapy has the effect of changing the D-Dimer level and so tests should not be performed on patients receiving either heparin or warfarin.