Haematology

Specialised Coagulation Services

Coagulation is often described as one of the most complex biochemical pathway and, as such, the investigation of bleeding and thrombotic disorders often require specialised testing to ensure correct diagnosis.

Special Coagulation Assays

Bleeding Disorders investigations

The Coagulation laboratories offer comprehensive testing for the diagnosis of Haemophilia (A & B) as well as other bleeding disorders such as von Willebrand’s Disease and platelet disorders. Specialised test used in the diagnosis of a bleeding disorder include:

• Platelet Function Analyser (PFA)
• von Willebrand screen including:
  • Factor VIII (8)
  • vWF antigen
  • vWF activity, Ricof, collagen Binding assay
  • vWFMultimers
  • Platelet aggregation studies

Further investigations may include:

• Rotem analysis (see below)
  
  

Thrombophilia investigations

The laboratories offerdiagnostic test for patients who have had thrombotic events such Deep Vein Thrombosis and Pulmonary Emboli. These patients will have a thrombophilia screen, including

• Antithrombin Activity
• Protein C Activity
• Protein S Free antigen
• Factor V Leiden
• Prothrombin Gene mutation
• Lupus Anticoagulant
• Anticardiolipin Antibodies
• Anti-Beta-2 Glycoprotein Antibodies

Haemophilia investigations

The correct diagnosis of Haemophila is very important and accurate determination of Factor VIII (8) or Factor IX (9) levels are important so that the clinicians can give optimal treatment.

There are two main types of factor assay used to measure Factor VIII (8):

• One stage Factor VIII (8) Assays using factor deficient plasma
• And Chromogenic Factor VIII (8) assays

Haemophilia patients treated with Factor VIII (8) of Factor IX (9) are at risk of producing inhibitors (antibodies against the treatment drug), these patients will have regular inhibitor screens.

Clotting Factor Assays

The laboratories offer (in addition to Factor VIII (8)) testing to identify the levels of individual clotting factors circulating in the patient’s plasma, these are:

Factor II (2); Factor V (5); Factor VII (7); Factor IX (9); Factor X (10); Factor XI (11); Factor XII (12)

Platelet Disorders

Vascular damage or injury results in platelet adhesion and aggregation at the site of damage, leading to the formation of a haemostatic plug. The inability to form such a plug can be linked to both inherited and acquired disorders, or induced by platelet inhibiting drugs or agents.

Platelet Function Analysis

The PFA-100 system is sensitive to platelet adherence and aggregation abnormalities and is dependent on normal von Willebrand factor, glycoprotein Ib and glycoprotein IIb/IIIa levels but not on plasma fibrinogen. Unlike aggregometry, the PFA-100 system measures the performance of platelets under flow conditions that simulate conditions in a damaged blood vessel.

Platelet aggregation studies

The platelet aggregation test checks to see how well platelets, a part of blood, clump together and cause blood clotting. Platelet aggregation disorders, where platelets fail to aggregate, may results in a serious bleeding disorder. The laboratories have several methodologies available to assess the platelet aggregation function, these include:

Lumi aggregation

As well as looking at how platelets aggregate the Lumi aggregation technique can measure what is released from platelets to promote aggregation. The Lumi aggregation test can be performed on a whole blood sample.

VWF Multimers

VWF multimeric analysis is a method for analysing the concentration and distribution of VWF multimers present in plasma. VWF multimer analysis is usually performed after functional and immunological VWF assays indicate an abnormality. Multimers can be used to classify VWD in to different sub-groups (Type I, Type 2 a,b,m) and Type 3).

Rotem

Occasionally despite intensive investigation no abnormality is found and then, depending on clinical presentation, a Rotem test may be performed. The Rotem test can be performedon a whole bloodand is more physiological than testing citrated plasma alone. The Rotem method can test the effectiveness and quality of platelet aggregation

HITT screening

Heparin Induced Thrombocytopenia and Thrombosis (HITT) is the development of thrombocytopenia (a low platelet count), due to the administration of various forms ofan anticoagulant called heparin. HITT predisposes to thrombosis, the abnormal formation of blood clots inside a blood vessel, and when thrombosis is identified the condition is called heparin-induced thrombocytopenia and thrombosis (HITT). HIT is caused by the formation of abnormal antibodies that activate platelets.

If someone receiving heparin develops new or worsening thrombosis, or if the platelet count falls, HIT can be confirmed with specific coagulation tests such as:

• A Rapid heparin / PF4 antibody screen
• A specific IgG antibody assay such as ELISA or Acustar

Research and Development

The laboratories are involved in a continuous process of evaluating new tests and techniques with field of coagulation. The Coagulation laboratories are currently reviewing the ACL AcuStar with a view to introducing this platform to the diagnostic analyser repertoire.

AcuStar

The ACL AcuStar is the first specialty-test analyser that offers full automation of highly sensitive immunoassays for the haemostasis lab. Labour-intensive specialty tests that previously required specialized training and up to two hours to perform, can now be performed in as little as 25 minutes, with no special training required.

The Acustar uses Chemiluminescence technology as an analytical technique with a wide working range and ability to detect very low concentrations of analytes. With chemiluminescent assays, the tracer (such as an antibody covalently linked to isoluminol) binds specifically to the target of the assay, emitting light when an oxidizer and catalyst are added. The light detector in the ACL AcuStar is highly sensitive and detects extremely low levels of light, significantly increasing the linearity (or working range) versus typical colorimetric assays.

This technique can be used to measure the following:

• Antibodies (IgG) responsible for Heparin induced Thrombocytopenia
  

Future assays

The Coagulation laboratory managers continue to assess the extensive repertoire of tests provided in an effort to meet the requirements of the service user.