APS and INR

Q: In patients with Anti-Phospholipid Syndrome (APS), PT/INR can be? - select one

A) falsely elevated

B) falsely lowered

Answer: A

Many patients with APS may have prolonged baseline PT/INR values. This is due to the effect of lupus anticoagulant. This is an in vitro artifact. 

This effect is further enhanced in aPTT measurement. Ideally, these patients should be monitored during anticoagulation therapy using alternative assays rather than standard PT and INR, such as an alternative thromboplastin reagent. 

The hematology service should be consulted, and the lab should be notified in such instances.

#rheumatology

#hematology

References:

1. Kasthuri RS, Roubey RA. Warfarin and the antiphospholipid syndrome: does one size fit all? Arthritis Rheum 2007; 57:1346.

2. Tripodi A, de Laat B, Wahl D, et al. Monitoring patients with the lupus anticoagulant while treated with vitamin K antagonists: communication from the SSC of the ISTH. J Thromb Haemost 2016; 14:2304.

3. Robert A, Le Querrec A, Delahousse B, et al. Control of oral anticoagulation in patients with the antiphospholipid syndrome--influence of the lupus anticoagulant on International Normalized Ratio. Groupe Méthodologie en Hémostase du Groupe d'Etudes sur l'Hémostases et la Thrombose. Thromb Haemost 1998; 80:99.

4. Tripodi A, Chantarangkul V, Clerici M, et al. Laboratory control of oral anticoagulant treatment by the INR system in patients with the antiphospholipid syndrome and lupus anticoagulant. Results of a collaborative study involving nine commercial thromboplastins. Br J Haematol 2001; 115:672.