What is the clinical significance of a positive aPL ab result? When should a physician suspect that a patient has APS?
Low-titer (usually IgM and transient) aCL abs are seen in 5% to 10% and LA in <1% of the normal healthy population.
Less than 1% will be persistently positive when retested a year later. aPL abs can occur de novo or be associated with an autoimmune disease, acute and chronic infections, medications, and neoplasms (especially lymphoma). Overall, the positive predictive value of an aPL ab predicting a future stroke, venous thrombosis, or recurrent fetal loss is between 10% and 25%, especially if the person is triple positive (LA, aCL, and anti-β2GPI), has LA or high-titer anti-β2GPI, has an autoimmune disease, and/or has cardiovascular risk factors (hypertension, smoking, diabetes, and hyperlipidemia).
APS should be suspected in any of the following situations:
- • Arterial thrombosis especially before the age of 50 years.
- • Unprovoked venous thrombosis especially before the age of 50 years.
- • Recurrent thrombosis.
- • Both arterial and venous thrombotic events in the same patient.
- • Thrombosis at unusual sites (e.g., renal, hepatic, cerebral sinuses, mesenteric, vena cava, retinal, and subclavian).
- • Obstetrical: fetal loss or recurrent miscarriages; early or severe preeclampsia; unexplained intrauterine growth restriction; HELLP syndrome.