Characterization of PLAC® Tests in the Quantization of Lipoprotein Associated Phospholipase A for Assessment of Cardiovascular Diseases

Background: PLAC® mass test (diaDexus, Inc.) does not detect all Lp-PLA proteins in the circulation. The total circulating Lp-PLA mass can be quantized by using the CHAPS modified PLAC® mass test. To compare the difference of the PLAC® mass, CHAPS modified PLAC® mass and PLAC® activity tests in risk assessment of CVD, the 3 Lp-PLA quantization methods were characterized using a collection of serum and plasma from CVD patents and matched non-symptomatic controls. Improvement on risk assessment for ischemic stroke by Lp-PLA and lipids were also investigated.

Methods: Ninety one human sera and plasma from elderly patients with first CVD incidents and 78 matched controls were collected at clinics. Lp-PLA was assessed by PLAC® mass, CHAPS modified PLAC® mass and PLAC® activity tests and data were subjected to statistical analyses. Correlation with lipid cholesterols or Apo proteins was compared for all formats of PLAC® tests. Ratios of Lp-PLA by different PLAC® tests to different lipids were assessed for synergistic enhancement in the indication of ischemic stroke.

Results: The PLAC® mass test was superior to other formats of PLAC® tests in the assessment of CVD and is independent of lipids. The Lp-PLA by the CHAPS modified PLAC® mass test has no separation between the CVD and control groups.

Conclusions: Both PLAC® mass and PLAC® activity tests are effective but the CHAPS modified PLAC® mass test has no or less utility in the risk assessment of CVD. The ratio of Lp-PLA by either PLAC® mass or PLAC® activity over ApoA1 or (Apo A1 + Apo B) synergistically enhance the risk assessment power for ischemic stroke.