空腹状态对血脂测定影响很小

患者在抽取血液进行血脂测定之前必须忍受清晨饥饿的情况可能将成为历史。基于越来越多的证据，空腹对多数患者的血脂水平和治疗决策并无太大影响。对2011年中期的6个月间进行血脂谱测定的200,000余名卡尔加里居民的回顾分析显示，抽血前空腹时间与血脂水平的无相关性很小。

布里格姆妇女医院的Amit V. Khera和Samia Mora博士在随刊述评中写道：“来自观察性研究和他汀临床试验的越来越庞大的证据体系提示，非空腹或空腹抽血的血脂测定均可用于心血管风险评估和治疗决策制定，尤其是当感兴趣的血脂亚类不是低密度脂蛋白(LDL)胆固醇时。”(Arch. Int. Med. 2012 Nov. 12 [doi: 10.1001/2013.jamainternmed.263])。

研究数据来自卡尔加里实验室服务机构的记录，服务人群约为140万人。在2011年4~9月期间，对209,180人进行血脂测定，无论其空腹持续时间如何。

研究结果提示，血脂测定，包括总胆固醇和高密度脂蛋白(HDL)胆固醇，受空腹状态的影响很小。无论空腹持续时间如何，上述两种指标的变化幅度均不超过2%。无论空腹持续时间如何，LDL胆固醇的变化幅度不超过10%，甘油三酯的变化幅度不超过20%。

Christopher Naugler博士

卡尔加里大学的Davinder Sidhu博士和Christopher Naugler博士说：“对于常规血脂水平测定，空腹在很大程度上是没有必要的。”对于初始甘油三酯测定超过400 mg/dl的患者，可考虑进行空腹血脂测定或直接测定LDL胆固醇(Arch. Int. Med. 2012 [doi: 10.1001/archinternmed.2012.3708])。

上述研究者一致认为， “鉴于目前缺乏空腹血脂测定更具优势的证据，故对于多数进行常规临床访视的患者而言，在非空腹状态下接受血脂测定是合理的。”

Sidhu博士和Naugler博士披露无相关利益冲突。Mora医生披露担任辉瑞和Quest诊断公司的顾问，并接受了雅培、阿斯利康和国家血脂协会提供的演讲报酬，还接受了阿斯利康公司提供的研究支持。Khera医生披露无相关利益冲突。

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By: MITCHEL L. ZOLER, Cardiology News Digital Network

Hungry mornings – as patients wait to get their fasting blood lipids drawn – may come to an end, based on more evidence that fasting has little meaningful impact on lipid levels and management decisions for most patients.

A review of lipid test profiles drawn from more than 200,000 Calgary residents during 6 months in mid-2011 showed that fasting time prior to the blood draw had little association with lipid subclass levels.

"The results presented herein, combined with those of other recent studies, suggest that nonfasting determination of lipid subclasses is a reasonable alternative to fasting determinations," said Dr. Davinder Sidhu and Dr. Christopher Naugler of the University of Calgary (Alta.), in a report published on Nov. 12 (Arch. Int. Med. 2012 [doi: 10.1001/archinternmed.2012.3708]).

Fasting lipid measures or direct measurement of low-density lipoprotein (LDL) cholesterol could be considered for patients with an initial triglyceride measurement greater than 400 mg/dL, they added.

"A growing body of evidence from observational studies and statin clinical trials suggests that nonfasting or fasting blood draws may be used for cardiovascular risk assessment and therapeutic decisions," especially when the lipid subfractions of interest are not LDL cholesterol, wrote Dr. Amit V. Khera and Dr. Samia Mora, both from Brigham and Women’s Hospital in Boston, in an invited commentary published online along with the study report (Arch. Int. Med. 2012 Nov. 12 [doi: 10.1001/2013.jamainternmed.263]). Lipid measures that are not very variable by fasting status include total and high-density lipoprotein (HDL) cholesterol, which each varied by less than 2% regardless of fasting duration. LDL cholesterol varied by less than 10%, and triglycerides varied by less than 20%, regardless of fasting duration.

"Given the current lack of evidence for the superiority of fasting lipid testing, it is reasonable to consider nonfasting lipid testing in most individuals who present for a routine clinic visit," said Dr. Khera and Dr. Mora.

They also noted several limitations in the study reported by Dr. Sidhu and Naugler: Most of the blood specimens in the analysis were drawn after at least 9 hours of fasting; because the duration of fasting was not randomized, people who presented to their laboratory nonfasting may differ from those who were fasting in important ways; and the people included in the study were primarily at low risk based on their relatively young age – an average of 53 years – and low total cholesterol level, a mean of 183 mg/dL.

Data for the study came from the records of Calgary Laboratory Services, which is the sole supplier of laboratory services for Calgary, and a population of about 1.4 million people. During the period of April-September 2011, blood samples for lipid measurements were drawn from 209,180 people regardless of fasting duration.

The results of the study suggest that "fasting for routine lipid level determinations is largely unnecessary," concluded Dr. Sidhu and Dr. Naugler.

Dr. Sidhu and Dr. Naugler said they had no disclosures. Dr. Mora disclosed that he has been a consultant to Pfizer and Quest Diagnostics, that he has received speaking honoraria from Abbott, AstraZeneca, and the National Lipid Association, and that he has received research support from AstraZeneca. Dr. Khera had no disclosures.

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Nonfasting Lipid Profiles Become Standard of Care

Requiring patients to fast before a lipid-profile blood draw poses several logistical challenges and inefficiencies. Patients are often inconvenienced by having to return to a health care site to give blood when they are fasting, and they may not show up at all. Laboratories are burdened by the relatively large number of patients who show up in the morning.

The finding reported by Dr. Sidhu and Dr. Naugler that total and HDL cholesterol levels vary little is quite useful. For example, if the goal is to collect lipid levels to calculate a patient’s Framingham risk score, much of the predictive value of a lipid profile is captured in these two stable parameters. Even when the main goal of measurement is to determine whether to treat dyslipidemia, a modest degree of imprecision is tolerable. With minimal variation in total and HDL cholesterol levels, non-HDL cholesterol levels can be easily calculated and used to determine a threshold for starting treatment. Similarly, total and HDL cholesterol levels can monitor response to treatment.

When triglyceride levels are the focus, fasting levels may be preferable, but only a very small fraction of lipid profiles are drawn for this purpose.

Given the results reported by Dr. Sidhu and Dr. Naugler, the benefits of getting a patient’s lipid profile when he or she is in the office seem to dominate; the incremental gain from a fasting profile is exceedingly small. Nonfasting lipid levels are arguably the standard for managing most patients.

J. MICHAEL GAZIANO, M.D., is professor of medicine at Harvard Medical School and Brigham and Women’s Hospital in Boston. He said that he had no disclosures. He made these comments in an editorial (Arch. Int. Med. 2012 [doi: 10.1001/jamainternmed.2013.1771]).