Variability of lipids in patients with Type 2 diabetes taking statin treatment: implications for target setting

To determine the biological variability of lipids in patients with Type 2 diabetes (T2DM) who are on statin treatment and then to assess any implications for current lipid targets.

A cross-over study of biological variation of lipids in 26 patients with T2DM taking either simvastatin 40 mg or atorvastatin 10 mg. After 3 months on one statin, fasting lipids were measured on 10 occasions over a 5-week period. Following 3 months on the other statin, 10 further samples were taken over 5 weeks. The main outcome measures were biological variability of total cholesterol (TC), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides.

The coefficient of variation (CV) of TC, LDL, HDL and triglycerides on simvastatin was 8.17, 13.11, 7.95 and 12.06%, respectively, whereas the CV on atorvastatin was 6.92, 10.30, 5.13 and 19.71%, respectively, with no statistically significant differences between statins. Treating to sustain a target TC < 5.0 mmol/l or LDL < 3.0 mmol/l means needing to maintain a mean TC of 4.3-4.4 mmol/l or LDL of 2.4-2.5 mmol/l. Treating to consistently achieve an LDL < 2.0 mmol/l means aiming for a mean of only 1.5-1.6 mmol/l.

In patients with T2DM taking either simvastatin or atorvastatin, the mean TC and LDL concentrations needed to consistently remain below a target are much lower than the target value itself. This means that guideline target limits extrapolated from the mean values of patients participating in clinical studies may overestimate the lipid reductions required.