Abstract Aims Examine whether the low-density lipoprotein cholesterol (LDL -C) determination method influences the rate of statin initiation for primary prevention of cardiovascular disease. Methods and results We conducted a register-based retrospective study in the Region of Southern Denmark. Two hospital-based laboratories in the region directly measure LDL -C whereas four laboratories calculate LDL -C using Friedewald's formula. Physicians do not choose which method is used. We included all statin-naïve patients ≥40 years with no history of cardiovascular disease, diabetes, or chronic kidney disease, who had their LDL -C determined during 2018–2019. There were 202 807 people who had LDL -C determined during the study period (median age 59 years, 44% women) of which 37% had a direct LDL -C measurement. The median reported LDL -C was 3.40 mmol/L [interquartile range (IQR) 2.90–4.00] for those with a direct measurement vs. 3.00 mmol/L (IQR 2.40–3.50) for those with calculated LDL -C. For those with direct measurement, re-calculated LDL -C (using Friedewald's formula) was 0.35 mmol/L lower than the reported direct LDL -C measurement. Among those with directly measured LDL -C, 3.6% initiated statins compared with 2.7% of those with a calculated LDL -C. Direct LDL -C measurement led to higher odds of having a statin initiated compared with calculated LDL -C (adjusted odds ratio 1.23, 95% CI 1.17–1.30); for those with triglycerides >1.7 mmol/L the adjusted odds ratio was 1.41 (95% CI 1.30–1.52). Conclusion Differences in the reporting of LDL -C from laboratories using different methods have a substantial influence on physician's decisions to prescribe statins.