Lipid Re-screening: What Is the Best Measure and Interval?

Osamu Takahashi ^1*, Paul P Glasziou ¹, Rafael Perera ¹, Takuro Shimbo ², Jiro Suwa ³, Sonoe Hiramatsu ³ and Tsuguya Fukui ⁴

¹ Department of Primary Health Care, University of Oxford, United Kingdom
² Department of Clinical Research and Informatics, International Medical Centre of Japan, Japan
³ Centre for Preventive Medicine, St. Luke's International Hospital, Japan
⁴ Division of General Internal Medicin, Department of Medicine, St. Luke's International Hospital, Japan

^* To whom correspondence should be addressed. E-mail: otakahas{at}gmail.com.

Accepted 2 June 2009

Abstract

Objectives: To estimate the long-term true change variation ("signal") and short-term within-person variation ("noise") of the different lipids measures and evaluate the best measure and the optimal interval for lipid re-screening.

Design: Retrospective cohort study from 2005 to 2008.

Setting: Centre for Preventive Medicine at a teaching hospital in Tokyo, Japan.

Participants: 15810 adults not taking cholesterol-lowering medications at baseline.

Main outcome measures: Annual measurement of the serum total cholesterol (TC), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and calculated the ratio of TC/HDL and LDL/HDL. We estimated the ratio of long-term drift ("signal") to the short-term within-person variation ("noise") for each measure.

Results: At baseline, participants (53% male) with a mean age of 49 years old (range: 21 to 92) and a mean TC level of 5.3 mmol/L (SD, 0.9 mmol/L) had annual check-ups over 4 years. Short-term within-person variations of TC, LDL, HDL, TC/HDL, and LDL/HDL were 0.12 (coefficient of variation (CV), 6.4%), 0.08 (CV: 9.4%), 0.02 (CV: 8.0%), 0.08 (CV: 7.9%) and 0.05(CV: 10.6%) mmol²/L² respectively. The ratio of signal to noise at 3 years was largest for TC/HDL (1.6), followed by LDL/HDL (1.5), LDL (0.99), TC (0.8), and HDL (0.7), suggesting cholesterol ratios are more sensitive re-screening measures.

Conclusion: The signal-to-noise ratios of standard single lipid measures (TC, LDL, and HDL) are weak over 3 years and decisions based on these measures are potentially misleading. The ratio, TC/HDL and LDL/HDL, appears to be better measure for monitoring assessments. The lipid re-screening interval should be more than 3 years for those not taking cholesterol-lowering drugs.