Moll and Ortel identified problems with the use of the prothrombin time (PT) and International Normalized Ratio (INR) for monitoring warfarin therapy in a patient with a lupus anticoagulant. Warfarin therapy in these patients should be monitored with an alternative method, since the PT may be unreliable. The authors are from Duke University.

Patient selection: presence of a lupus anticoagulant


Indications for monitoring the patient with an alternative method:

(1) prolongation of the PT in the absence of oral anticoagulation and Factor VII deficiency (some patients with a lupus anticoagulant will show an elevation in the PT in addition to the usual increase in the PTT)

(2) variation in the INR reported by different laboratories while on stable warfarin therapy (due to differing sensitivities to the anticoagulant shown by the different thromboplastins)

(3) discordance between clinical status and reported INR (bleeding with low INR, thrombosis with high INR)


Alternative methods that are less affected by the anticoagulant:

(1) chromogenic Factor X

(2) prothrombin-proconvertin time

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