Triglyceride-dependent discordance in routine LDL cholesterol reporting during postprandial lipaemia: a self-controlled repeated-measures study

Background Non-fasting lipid testing is increasingly used in clinical practice, but postprandial triglyceride-rich lipoproteins may affect calculated low-density lipoprotein cholesterol (LDL-C). This study evaluated triglyceride-dependent discordance among routine LDL-C reporting methods during postprandial lipaemia.Methods Sixty-two Chinese adults underwent lipid profiling under three conditions: fasting, 4h after a habitual mixed meal test, and 4h after a standardised oral fat tolerance test. LDL-C measured by a homogeneous chemical masking assay was used as a routine comparator, not a reference method. Friedewald, Vujovic and Sampson estimates were compared with LDL-CCM using ±12% concordance, bias and triglyceride-stratified analyses. As a secondary analysis, non-HDL-C and apolipoprotein B were assessed for within-participant stability during the oral fat tolerance test.Results Median triglyceride concentrations increased from 1.23 mmol/L fasting to 2.16 mmol/L after the mixed meal test and 3.46 mmol/L after the oral fat tolerance test. Concordance between calculated LDL-C and LDL-CCM declined as triglycerides increased and was lowest after oral fat loading. Agreement was relatively preserved at triglycerides <2.0 mmol/L, decreased substantially at 2.0–4.52 mmol/L and was poor above formula applicability ranges. Non-HDL-C and apolipoprotein B showed limited median changes from fasting to 4h after the oral fat tolerance test (+2.1% and −4.3%, respectively).Conclusions Postprandial lipaemia was associated with triglyceride-dependent discordance among routine LDL-C reporting methods. Without a reference LDL-C method, these findings indicate inter-method discordance rather than absolute measurement error. Triglyceride concentration and formula applicability limits should be considered when interpreting LDL-C in lipaemic samples, with non-HDL-C and apolipoprotein B providing complementary information.