Cholesterol
Cholesterol: Variations in Practice
Project Leads: Dr Helen Doll, Maria Vazquez Montes and Dr Rafael Perera
Monitoring of cholesterol levels has become an extremely common activity in primary care. What we do not yet know is the optimal interval for cholesterol monitoring. In a recent paper we estimated the variation in initial response to treatment and the long-term drift from initial response in patients receiving cholesterol-lowering medications. We also looked at the detectability of long-term changes in on-treatment cholesterol level ("signal") given short-term, within-person variation ("noise"). We found that the signal-noise ratio in cholesterol level monitoring is weak. The signal of a small increase in cholesterol level is difficult to detect against the background of a short-term variability of 7%. In annual re-checks in adherent patients, many apparent increases in cholesterol level may be false positive. These findings suggest that the interval for monitoring patients who are receiving stable cholesterol-lowering treatment could be lengthened.
Cholesterol Monitoring in Oxfordshire
Project Lead: Dr Helen Doll
The use of laboratory tests has increased dramatically over the last decades. To assess the rise in use of lipid measurements, and to determine how much of the testing was repeat testing, we analysed the rates of lipid testing (total cholesterol, HDL, and triglyceride) in Oxfordshire during the last 20 years. All tests which were the third or more in a three-year period were considered to be for monitoring. A substantial rise in the number of tests was observed during the past 10 to 15 years, with much of this appearing to be for monitoring purposes rather than for case finding or risk assessment. Mean cholesterol levels generally increased with increasing number of tests performed during each three year period until 1999-2001, but decreased with every repeat test in later years; this may reflect the effectiveness of statins in reducing serum cholesterol and the rise in later years of the use of monitoring during such treatment.
Optimal Cholesterol Monitoring (re-analysis of LIPID trial data)
Investigators: Paul Glasziou
Cholesterol level monitoring is a common clinical activity, but the optimal monitoring interval is unknown and practice varies. We aimed to estimate, in patients receiving cholesterol-lowering medication, the variation in initial response to treatment, the long-term drift from initial response, and the detectability of long-term changes in on-treatment cholesterol level ("signal") given short-term, within-person variation ("noise").
Cholesterol pre-treatment
Investigators: Paul Glasziou, Rafael Perera, Carl Heneghan
To evaluate the best measure and the optimal interval for lipid re-screening, we used a retrospective cohort study at a teaching hospital in Tokyo, Japan of 15810 adults not taking cholesterol-lowering medications at baseline. 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. 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%) mmol(2)/L(2) respectively. The ratio of signal to noise at three 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.