Immunonephelometric/turbidimetric apolipoprotein B assays for the clinical laboratory

Non-High-Density Lipoprotein Cholesterol and Guidelines for Cholesterol Lowering in Recent History

BACKGROUND

The National Cholesterol Education Program (NCEP) released guidelines for treating cholesterol in 1988, 1994, and 2002. After a hiatus, the guidelines were released again in 2013, 2016, 2017, and 2018.

METHODS

In this article, I review these guidelines, factors that affected their release, how they evolved, and why recommended treatment targets are reasonable. Also, to aid reader understanding, I briefly discuss biochemical mechanisms and the pathophysiology of beta-lipoproteins, focusing on the importance on non-high-density cholesterol (non-HDLC) in assessing risk and as a target for treatment. The concepts discussed are important to laboratory clinicians because those workers inscribe target values on the reports and may consult with medical staff members.

CONCLUSIONS

The newest recommendations, released in 2018, are an extension of the 2017 guidelines that defined non-HDLC as equivalent to low-density lipoprotein cholesterol (LDLC). For the reasons discussed herein, non-HDLC has advantages over LDLC. Laboratories reporting cholesterol results should include non-HDLC values and cutoffs in their reports.

Serum cholesterol and apolipoprotein B levels may reflect disease activity in ovarian cancer patients

Data in the literature demonstrates increased receptor-mediated uptake of low density lipoprotein (LDL) in many types of malignant cells compared with normal cells. In acute leukemia, an inverse correlation has been demonstrated between disease activity and plasma cholesterol. To explore whether this is true also for ovarian cancer a case-control study was performed. We serially collected blood samples and assayed serum cholesterol and apolipoprotein B (the receptor recognizing moiety of LDL) in 10 patients with ovarian cancer. At diagnosis, the patients had lower mean cholesterol levels compared with 6 healthy women. An increase was found after primary surgery and after successful initial chemotherapy. The 5 patients who are in complete remission after a mean follow-up time of 79 months had higher cholesterol and apolipoprotein B levels at their last visit than at diagnosis. In contrast, a reduction of the two analytes was found in the patients who died from their ovarian cancer 15 to 28 months after diagnosis. The results may open a possibility for targetted chemotherapy in ovarian cancer with LDL as a drug carrier.

Relationships between triglycerides, lipoproteins, glucose and coronary artery disease

We examined the relationship of apolipoprotein B (apo B), glucose, triglycerides and other lipoprotein lipids to coronary artery disease (CAD). Using receiver-operating characteristic curves (ROC), we noticed that the triglyceride ROC curve crossed above other lipoprotein curves at a triglycerides level of approximately 1.4 g/l. We examined subgroups of < 1.4 g/l and > 1.4 g/l. ANOVA (F = 18.9, P < 0.0001) and stepwise logistic regression (P = 0.0002) indicated that triglycerides were the best predictor in the < 1.4 g/l group. The best markers in the > 1.4 g/l group were low density lipoprotein cholesterol and apo B. Glucose did not appear to significantly alter the predictive power of triglycerides. These data suggest that triglyceride appears to be an overall significant univariate marker for CAD because of its effect at lower concentrations. The strong relationship between CAD and triglycerides at low triglyceride levels may reflect increased levels of very low density lipoprotein metabolites in some individuals. We conclude that some triglyceride-rich particles are independently atherogenic, that glucose did not alter this relationship and that when the samples were split into those with high and low levels of triglycerides, triglycerides and apo B but not HDLC was a significant predictor of CAD.