Comparison of Two Nuclear Magnetic Resonance Spectroscopy Methods for the Measurement of Lipoprotein Particle Concentrations

Triglyceride/HDL cholesterol ratio and lipoprotein insulin resistance Score: Associations with subclinical atherosclerosis and incident cardiovascular disease

BACKGROUND

The triglyceride/HDL cholesterol (TG/HDL-C) ratio and the Lipoprotein Insulin Resistance (LP-IR) score are lipid markers of insulin resistance. Their associations with carotid intima media thickness (cIMT; subclinical atherosclerosis) and incident cardiovascular disease (CVD) have not been thoroughly investigated.

METHODS

In a cross-sectional cohort (89 subjects without type 2 diabetes (T2D) and 81 subjects with T2D we determined cIMT (ultrasound), homeostasis model assessment of insulin resistance (HOMA-IR) and the TG/HDL-C ratio. The LP-IR score, based on 6 lipoprotein characteristics determined by nuclear magnetic resonance spectroscopy, was measured in 123 participants. A prospective study was carried out among 6232 participants (Prevention of REnal and Vascular ENd-stage Disease study).

RESULTS

Cross-sectionally, the adjusted associations of HOMA-IR, the TG/HDL-C ratio and the LP-IR score with cIMT were approximately similar (standardized β = 0.34 (95 % CI 0.19-0.48), 0.24 (95 % CI 0.09-039) and 0.41 (95 % CI 0.23--0.59), respectively). Prospectively, 507 new cases of CVD were observed after a median follow-up of 8.2 (interquartile range 7.5-8.8) years. HOMA-IR, the TG/HDL-C ratio and LP-IR were each associated with incident CVD independent of potential confounders (HR 1.12, 95 % CI 1.02-1.24;1.22, 95 % CI 1.11-1.35 and 1.15. 95 % CI 1.01-1.31, respectively). The association of the TG/HDL-C ratio with incident CVD was somewhat stronger than that of HOMA-IR.

CONCLUSION

Lipoprotein-based markers of insulin resistance are at least as strongly associated with subclinical atherosclerosis and clinical atherosclerosis development as HOMA-IR, obviating the need to measure insulin to determine the impact of insulin resistance. For practical purposes, the easily obtainable TG/HDL-C ratio may suffice.

[Laboratory diagnostics of lipid metabolism disorders]

Clinically, disorders of lipid metabolism often remain without symptoms. Typical skin lesions, however, can be indicative. Secondary hyperlipoproteinemias (HLP) are more common than primary hyperlipoproteinemias; they can (partially) be improved by treating the underlying disease. Basic diagnostics consist of the determination of cholesterol, triglycerides, LDL cholesterol and HDL cholesterol. To exclude secondary HLP, glucose, HbA1C, TSH, transaminases, creatinine, urea, protein and protein in the urine are useful. Since virtually all routine methods for LDL-C are biased by high triglycerides, lipoprotein electrophoresis is indicated for triglycerides above 400 mg/dl (4.7 mmol/l). Primary HLPs have known or yet unknown genetic causes. Primary hyperlipidemias should be taken into consideration especially in young patients with an LDL cholesterol concentration are above 190 mg/dl (4.9 mmol/l) and/or triglycerides above 400 mg/dl (10 mmol/l) and secondary HLP (obesity, alcohol, diabetes mellitus, kidney disease) is excluded. The basic diagnostics is meaningfully extended by the measurement of lipoprotein (a) (Lp(a)). It is indicated in moderate and high risk of vascular disease, progression of atherosclerosis in "well-controlled" LDL cholesterol, familial clustering of atherosclerosis or high Lp(a), evidence for elevated Lp(a) coming from lipoprotein electrophoresis, aortic stenosis and in patients in whom statins have a poor effect. Genetic diagnostics needs to be considered if primary HLP is suspected. It is most frequently conducted for suspected familial hypercholesterolemia and has already been recommended in guidelines.