What is the workup for a prolonged activated partial thromboplastin time (aPTT) in a 2-year-old child?

From the Guidelines

The workup for a prolonged activated partial thromboplastin time (aPTT) in a 2-year-old should begin with a thorough history and physical examination, followed by a repeat aPTT, prothrombin time (PT), complete blood count (CBC), and mixing study, using age, analyzer, and reagent appropriate reference ranges, as recommended by 1. The initial evaluation should focus on identifying potential causes of the prolonged aPTT, including bleeding symptoms, family history of bleeding disorders, and medication use.

• Key laboratory tests include:
  • Repeat aPTT to confirm the abnormality
  • Prothrombin time (PT) to assess the extrinsic coagulation pathway
  • Complete blood count (CBC) to evaluate for thrombocytopenia or other cytopenias
  • Mixing study to differentiate between factor deficiencies and inhibitors, as described in 1
• If the aPTT corrects with normal plasma, a factor deficiency is likely, while persistent prolongation suggests an inhibitor.
• Specific factor assays should then be performed, particularly for factors VIII, IX, XI, and XII, as deficiencies in these are common causes of isolated aPTT prolongation, as noted in 1.
• Von Willebrand factor (vWF) antigen and activity should also be measured, as von Willebrand disease can present with prolonged aPTT.
• If an inhibitor is suspected, a Bethesda assay can quantify factor VIII inhibitors, as recommended in 1.
• Lupus anticoagulant testing may be warranted, even in young children, as it can cause a prolonged aPTT without bleeding symptoms. The timing of blood draws is crucial, as crying and struggling can activate coagulation factors and affect results, highlighting the importance of using age-appropriate reference ranges, as emphasized in 1.
• Consultation with a pediatric hematologist is recommended for interpretation of results and management planning, especially if a significant bleeding disorder is identified.

From the Research

Workup for Prolonged aPTT in a 2-Year-Old

• The workup for prolonged activated partial thromboplastin time (aPTT) in a 2-year-old involves several steps to determine the underlying cause of the prolongation 2, 3, 4, 5, 6.
• The aPTT test is used to screen for intrinsic coagulation factor deficiency, and prolongation of the aPTT suggests a bleeding tendency or the presence of lupus anticoagulant (LA) 2.
• A cross-mixing test can be used to detect LA and differentiate it from factor deficiencies 2, 3, 6.
• The cross-mixing test involves mixing patient plasma with normal plasma at various ratios and measuring the aPTT value 2.
• If the aPTT value corrects with the addition of normal plasma, it suggests a factor deficiency, while a lack of correction suggests the presence of an inhibitor such as LA 3, 4.
• The index of circulating anticoagulant (ICA) can also be used to predict the presence of LA, with a cutoff value of 11% having high sensitivity and specificity 4.
• Mixing studies can be useful in identifying the underlying cause of prolonged aPTT, but may not always be necessary and can occasionally be omitted 6.
• The choice of test and interpretation of results should be guided by clinical context and laboratory expertise 3, 4, 5, 6.