Interpretation of Your Coagulation Results

What Does This Pattern Mean?

1. Factor VII Deficiency (most specific cause)

• Factor VII is the only clotting factor that belongs exclusively to the extrinsic pathway
• A prolonged PT + normal aPTT localizes the defect precisely to the extrinsic pathway
• It is the most common autosomal recessive coagulation factor deficiency
• Importantly, there is poor correlation between Factor VII levels and bleeding severity - some patients with very low levels bleed minimally
• Confirmed by specific Factor VII assay showing reduced activity
• Mixing study (adding normal plasma) will correct the PT if it is a true deficiency rather than an inhibitor
• Quick Compendium of Clinical Pathology, 5th Ed.

2. Early Vitamin K Deficiency

• Factor VII has the shortest half-life (~4-6 hours) of all the vitamin K-dependent factors (II, VII, IX, X)
• When vitamin K becomes deficient, Factor VII drops first, causing isolated PT prolongation before aPTT is affected
• Later, as deficiency deepens, Factors II, IX, and X also fall, prolonging aPTT as well
• Causes include: poor diet, malabsorption (fat-malabsorption syndromes, bile duct obstruction), prolonged antibiotic use (destroys gut flora that produce vitamin K)
• Harrison's Principles of Internal Medicine, 22nd Ed.

3. Warfarin / Oral Anticoagulant Effect (Low Dose)

• Warfarin inhibits vitamin K-dependent clotting factors; at low doses, it first prolongs PT/INR
• If the patient is on warfarin or recently started it, this would explain the picture

4. Direct Factor Xa Inhibitors (e.g., rivaroxaban, edoxaban)

• Can prolong PT; notably apixaban may show a normal PT
• Worth ruling out if patient is on anticoagulant medication

5. Liver Disease (Mild/Early)

• The liver produces clotting factors; early liver dysfunction reduces Factor VII first due to its short half-life
• However, your question states all other investigations are normal, making this less likely

Summary Table (Harrison's, Table 69-3)

Most Likely Diagnosis in Your Case

1. Early Vitamin K deficiency - most common acquired cause
2. Congenital Factor VII deficiency - if no identifiable acquired cause
3. Low-dose warfarin effect - if on medications

Next Step

• Administer Vitamin K (oral or IV) and repeat PT/INR in 24-48 hours - if it corrects, vitamin K deficiency is confirmed
• If it does not correct, send a Factor VII activity assay for congenital deficiency
• Check medication history, diet, fat malabsorption symptoms

Sources: Harrison's Principles of Internal Medicine 22E, Goldman-Cecil Medicine, Quick Compendium of Clinical Pathology 5th Ed., Tintinalli's Emergency Medicine