In this study, prominently elevated levels of TG and RC were found in the non-fasting group when compared with those in the fasting one, which is similar to the finding of the studies with a large-scale general population in Denmark [8, 15, 16]. In those Danish studies, the comparison between fasting and non-fasting blood lipid levels was carried out in different subjects according to the time of visiting the clinics [15, 16]. The significant elevation of non-fasting TG and RC levels after a daily meal was also observed in 33 fasting outpatients with HBP in this study. Moreover, the mean TG level of the fasting outpatients was more than 1.7 mmol/L and that of the non-fasting outpatients exceeded 2.0 mmol/L, indicating the augmented synthesis and/or reduced elimination of TRLs and their remnants after a daily meal in Chinese patients with HBP.
Conversely, the non-fasting group had significantly lower levels of TC, LDL-C and non-HDL-C than the fasting group, which was similar to the finding of a Danish study carried out in different subjects according to the time of visiting the clinics . We recently observed the non-fasting reduction in levels of TC, LDL-C and non-HDL-C in the inpatients with overweight, coronary heart disease or not [17–19]. There were several possible explanations for the non-fasting reduction in those lipid parameters. First, the decrease in non-fasting levels of TC, LDL-C and non-HDL-C was likely due to hemodilution caused by dietary fluid intake [20, 21]. Second, increased TRLs and their remnants after a daily meal could activate cholesteryl ester transporter protein in the case of hypertriglyceridemia, which ultimately increased RC levels and decreased LDL-C through promoting the transfer of cholesteryl ester from LDL to TRLs and their remnants [22, 23]. It is noteworthy that there was no significant difference in HDL-C level between the two groups, which was consistent with the results of other researchers who confirmed that HDL-C level was not affected by food intake .
We recently reported that the non-fasting cut-off values to determine HTG or HRC in Chinese subjects were very close to those recommended by the EAS (12), which induced that the corresponding percentages of non-fasting HTG or HRC dependent on those values were also very similar. Compared with the fasting group, the non-fasting group exhibited higher percentages of HTG and HRC. Although the difference in the percentages of HTG or HRC between the non-fasting group and the fasting one could not be statistically analyzed, the higher percentage of HTG in the non-fasting group still suggested that non-fasting blood lipid test could increase the probability of detecting HTG in Chinese outpatients with HBP.
Interestingly, the difference in the percentages of fasting and non-fasting HTG was small and insignificant in 33 outpatients with HBP. In addition to the small sample size, another cause for this phenomenon could be the difference in the time of blood lipid test. We previously found that levels of TG and RC began to rise at 2 h and peaked at 4 h after a daily meal in Chinese in patients with coronary heart disease and HBP [13, 14]. For some patients who are used to a high-fat and high-calorie diet, the peak of TG level may be higher or later [24, 25]. It indicated that serum TG level at 4 h after a daily meal can better reflect the maximum ability to synthesize and metabolize TG in a certain individual, while serum TG level at 2 h after a daily meal should be a relatively closer value to fasting level in Chinese subjects . In the non-fasting group, about 44% outpatients (n=61) were tested at 2 h after a daily breakfast, about 56% (n=78) were tested later than 2 h after a daily breakfast or even after a daily lunch. It was consistent with the finding that the mean TG level in the non-fasting group was more than 3.0 mmol/L while that at 2 h in 33 outpatients was about 2.5mmol/L. Moreover, it was reported that the average TG level after a daily lunch is higher than that at 2 h after a daily breakfast in Chinese subjects , which could be attributed to the additive effect of increasing TG by breakfast and lunch. Thus, TG level at 2 h after a daily meal may substitute its fasting value to evaluate HTG according to the non-fasting cut-off value for some special patients who are prone to hypoglycemia and physical weakness, such as diabetics, pregnant women, the elderly and children. However, in order to improve the diagnostic positive rate of HTG or to detect the maximum response of TG increase after a daily meal, blood lipid test at 4 h after a daily lunch could be more appropriate.
Chinese outpatients had little knowledge of the concept of non-fasting blood lipid test. Among the surveyed outpatients, less than one in five ones chose non-fasting blood lipid test. The vast majority of them chose fasting testing, which shows that this view has been widely accepted. After brief communication and notification on non-fasting blood lipid test, nearly half of them turned to accept non-fasting lipid test although more than one-third of them still insisted on fasting blood lipid test. It was worth noting that about one third of the surveyed outpatients left the decision to receive fasting or non-fasting blood lipid test to their doctors. That is to say, the application of non-fasting test in those subjects depends on their doctors. It indicates that the concepts of both doctors and patients must be updated through education in order to promote non-fasting blood lipid test in clinical practice in China.
There were several limitations in this study. First, the sample size was relatively small, especially compared with large-scale population studies abroad [8, 9]. Second, given the crucial role of controlling LDL-C levels in the prevention of cardiovascular disease in HBP patients, non-fasting LDL-C levels also should be evaluated in HBP patients. Since the goal of LDL-C level in HBP patients depends on the corresponding cardiovascular risk determined by underlying diseases and risk factors, it will be more complex than the determination of non-fasting HTG or HRC. In the future, prospective studies about non-fasting LDL-C levels to assess the risk of cardiovascular diseases in Chinese patients with HBP and guide clinical therapeutics are needed.