Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1059 page)

   Consensus panel recommendations are for Lp-PLA
₂
assessment in moderate-risk individuals for CHD either independently or in conjunction with hsCRP.

   Interpretation

   Concentrations ≥235 ng/mL are associated with increased risk of cardiovascular events, including myocardial infarction and ischemic stroke, and are predictive of short-term mortality in myocardial infarction patients.

   Elevated Lp-PLA
₂
has been found to be associated with ischemic stroke and may be useful in risk assessment.

   Limitations

   Smoking increases Lp-PLA
₂
measurements.

Suggested Reading

Corson MA, Jones PH, Davidson MH. Review of the evidence for the clinical utility of lipoprotein-associated phospholipase A2 as a cardiovascular risk marker.
Am J Cardiol.
2008;101(12A):41F–50F.

LUPUS ANTICOAGULANT (LA)
*

   Definition

   LAs are heterogeneous IgG or IgM autoantibodies that inhibit phospholipid-dependent assays of blood coagulation. Because phospholipid is essential for several steps in the coagulation cascade, the presence of LAs can prolong various phospholipid-dependent clotting times, such as PTT, PT, and the dilute Russell viper venom time (dRVVT, see p. 927).

   Use

   None of the tests mentioned in the Definition discussion is sufficiently sensitive to detect all LAs; therefore,
two screening tests
are required before LA can be excluded.

   The most commonly used screening tests are PT (1:100 diluted) and dRVVT. (Kaolin or micronized silica clotting time is no longer in use.) A positive screening test (prolonged dilute PT or dRVVT) requires confirmation by adding excess phospholipids in the test.

   Interpretation