What is the initial approach to testing for clotting disorders?

From the Guidelines

The initial approach to testing for clotting disorders should begin with a thorough medical history and physical examination, followed by first-line laboratory tests, including a complete blood count (CBC), prothrombin time (PT), and activated partial thromboplastin time (aPTT), as recommended by the 2008 NHLBI/NIH guidelines 1. These initial tests help identify abnormalities in the coagulation pathway and screen for platelet abnormalities.

• A CBC is essential to evaluate for thrombocytopenia or thrombocytosis, which can be a cause of bleeding or clotting disorders.
• PT and aPTT are critical for assessing the extrinsic and intrinsic pathways of coagulation, respectively. If the initial clinical evaluation suggests a bleeding disorder, such as von Willebrand disease (VWD), additional tests, including VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo), and factor VIII coagulant activity (FVIII), should be considered 1. It is also important to note that the timing of testing is crucial, as acute thrombotic events or ongoing anticoagulant therapy can affect results, so testing should ideally be performed when the patient is not in an acute phase and, if possible, after temporary discontinuation of anticoagulants (when safe to do so). In cases where the initial tests reveal abnormalities or if clinical suspicion remains high despite normal results, more specialized second-tier testing can be ordered based on the suspected disorder, such as specific factor assays or genetic testing for inherited thrombophilias 1.

From the Research

Initial Approach to Testing for Clotting Disorders

The initial approach to testing for clotting disorders typically involves a combination of laboratory tests to evaluate the coagulation pathway.

• The prothrombin time (PT) and activated partial thromboplastin time (APTT) are among the most commonly ordered coagulation tests 2.
• These tests are used to measure the clotting ability of plasma and are essential in evaluating patients suffering from bleeding disorders 3.
• The PT and APTT tests can help identify deficiencies in coagulation factors, such as factors VIII, IX, and XI, which are commonly associated with bleeding disorders 4.

Interpretation of Test Results

• Abnormal results from these tests, such as prolonged PT and APTT, may pose a diagnostic dilemma, especially in patients with multiple mild coagulation factor deficiencies 5.
• In such cases, the PT and APTT values may not always correlate with the severity of the bleeding disorder, and further testing may be necessary to determine the underlying cause of the abnormal results 6.
• A good understanding of the sensitivity of APTT reagents to heparin, lupus anticoagulant, and clotting factors is essential in interpreting test results and guiding further investigation 4.

Common Indications for Testing

• The most common indications for ordering PT and APTT tests include anticoagulant monitoring, initial evaluation of hemorrhage, and preoperative screening 2.
• However, the use of these tests as a routine preoperative screening tool is not generally recommended, as abnormal results may not always be clinically significant 6.
• In patients with suspected bleeding disorders, a combination of PT, APTT, and other specialized tests, such as factor assays, may be necessary to establish a definitive diagnosis 3, 4.