Fasting lipid specimen collection.

Q I was taught that the best specimen for a lipid profile is drawn in the early morning from a patient in the basal state who has been fasting for 10 to 12 hours. Upon researching this, I found mention of the fasting requirement, but I found no stipulation that the specimen should be drawn in the early morning. Are there no significant metabolic changes that might interfere with accurate lipid testing if, for instance, a fasting patient presents to the lab in the afternoon?

A We asked two experts in lipid chemistry to answer this question. Their answers reflect somewhat different perspectives on the issue.

--Dan Baer

Answer 1

There are three subquestions asked in this question. The first subquestion asks, "What is the basis for basal-state fasting for 10 to 12 hours?" A basal-state lipid profile fasting specimen determined by fasting overnight for nine to 12 hours is recommended for collection of a specimen for measurement of the lipid profile of total cholesterol, triglyceride, and HDL cholesterol, mainly because of the highly variable triglyceride diurnal variation. (1) In a study of the postprandial state after a fatty meal, it was observed that the individual plasma triglyceride levels after eight hours returned near to the fasting state in controls; however, in patients with coronary artery disease, triglyceride levels declined quickly, yet were still elevated. (2) The maximum daily rhythmic variation ranges from the daily mean to 63% for triglyceride concentration. (3)

Examination of cholesterol in fed and fasted states revealed that cholesterol concentrations measured in the fed individual differ significantly from those measured in the fasted individual and that plasma must be obtained after a minimum fasting time of 12 hours if an individual's risk of coronary heart disease is to be accurately assessed. (4) Long-term total fasting without glucose intake for three or more days results in ketosis that is associated with a large increase in serum total and LDL cholesterol. (5) Most clinical chemists assume that, in most patients, the minimal diurnal increases in VLDL cholesterol with a compensating small decrease in LDL cholesterol occurring after a meal usually do not appreciably affect the medical usefulness of the total cholesterol values.

The second subquestion asks, "What time in the afternoon is best to collect blood from patients who missed the morning fasting time or who work on night shifts?" Increased triglyceride levels were found in shift workers who followed a rotating morning, afternoon, and night shift for more than one year and whose blood was drawn between 7 a.m. and 8 a.m. at the beginning of a morning shift after a 12-hour fast. (6) In another study, which compared shift and day workers with a morning blood collection after a night's sleep and eight hours of fasting, it was confirmed that elevated triglycerides occurred in rotation-shift workers and that alcohol intake was not associated with the triglyceride elevation. (7)

Sleep deprivation (suspected to be part of the source causing elevated lipids in night-shift workers) was studied for five days and followed with blood sampling at 9 a.m. and 9 p.m. (8) Thus, plasma triglycerides and cholesterol, which gradually decreased over the first three days and decreased sharply over the fourth and fifth days of sleep deprivation, do not contribute to the elevated lipid levels of night-shift workers. For collection of cholesterol and lipoprotein serum specimen in the afternoon from night-shift workers, special basal-state conditions have been recommended for blood collection between 3 p.m. and 8 p.m. after a six-to nine-hour fast. (9) This recommendation also appears applicable to patients who miss the morning blood collection.

The third subquestion asks, "Do significant lipid and lipoprotein metabolic changes occur during the day that might interfere with accurate lipid testing?" Terpstra and colleagues demonstrated that patients who are meals at 9 a.m., 12 noon, and 5 p.m. had fasting triglyceride levels at minimum values between 3 a.m. and 5 a.m. After breakfast, a large rise continued until about 3 p.m. Then, a continuing overall fall occurred until triglyceride levels reached a basal value range between 1 a.m. and 7 a.m. They observed that a cholesterol pattern clearly followed the triglyceride pattern in patients with high triglycerides. (10) Samples taken hourly for eight hours from individuals who had eaten the same meal demonstrated that postprandial concentrations of triglycerides were higher for those who ate at night before 1 a.m. than for those who are during the day before 1 p.m. In contrast, mean cholesterol concentrations were lower after the night meal than after the day meal. (11)

Cohn and colleagues observed that the magnitude of postprandial triglyceridemia is dependent on age and sex and that many subjects have more than one triglyceride postprandial peak. (12) Sharrett and colleagues concluded that major determinants of fasting triglycerides are diabetes, obesity, insulin resistance, and gender; they also concluded that major determinants of postprandial triglycerides are fasting triglycerides, smoking, diet, creatinine, and alcohol. (13) Multiple other preanalytical biological, behavioral, and environmental factors influence variation in cholesterol and triglyceride fasting and postprandial values. (14)

In a telephone consultation with four clinical laboratory directors, concern was expressed about the patient who lives many miles from the lab failing to have blood collected and being sent home to return at a later date. They felt that applying some of the criteria for blood collection with the patient's interest at hand is needed. They suggest that, at such times, the blood should be collected and a note should be sent to the physician stating under what conditions the blood was collected.

In general, if a fasting patient presents to the laboratory in the afternoon, it appears reasonable to suggest that the blood be collected between 3 p.m. and 8 p.m. after at least a six- to nine-hour fast.

--Gerald R. Cooper, PhD, MD

Research Medical Officer

Clinical Chemistry Branch

Division of Laboratory Sciences, National Center for Environmental Health

Centers for Disease Control and Prevention 

Atlanta, GA

References

1. Stein EA, Myers GL. National cholesterol education program recommendations for triglyceride measurement; executive summary. Clin Chem. 1995;41:1421-1426.

2. Patsch JR, Miesenbock G, Hopferwieser T, et al. Relation of triglyceride metabolism and coronary artery disease. Studies in the postprandial state. Arterioscler Thromb. 1992;12:1336-1345.

3. Rivera-Coll A, Fuentes-Arderiu X, Diez-Noguera A. Circadian rhythmic variations in serum concentrations of clinically important lipids. Clin Chem. 1994;40:1549-1553.

4. Cohn JS, McNamara JR, Schaefer EJ. Lipoprotein cholesterol concentrations in the plasma of human subjects as measured in the fed and fasted states. Clin Chem. 1988;34:2456-2459.

5. Kartin BL, Man EF, Winkler AW, Peters JP. Blood ketones and serum lipids in starvation and water deprivation. J Clin Invest. 1944;23:824-835.

6. Romon M, Nuttens MC, Fievet C, et al. Increased triglyceride levels in shift workers. Am J Med. 1992;93:259-262.

7. Knutsson A. Relationships between serum triglycerides and gamma-glutamyltransferase among shift and day workers. J Intern Med. 1989;226:337-339.

8. Vondra K, Brodan V, Dobiasova M, Vitek V, Kopecka J. Effect of sleep deprivation on cholesterol metabolism and triglyceridaemia in male volunteers. Eur J Appl Physiol. 1986;55:83-87.

9. Emberson JR, Whincup PH, Walker M, Thomas M, Alberti KGMM. Biochemical measures in a population-based study: effect of fasting duration and time of day. Ann Clin Biochem. 2002;39:493-501.

10. Terpstra J, Hessel LW, Seepers J, Van Gent CM. The influence of meal frequency on diurnal lipid, glucose and cortisol levels in normal subjects. Eur J Clin Invest. 1978;8:61-66.

11. Romon M. Le Fur C, Lebel P, Edme JL, Fruchart JC, Dallongeville J. Circadian variation of postprandial lipemia. Am J Clin Nutr. 1997;65:934-940.

12. Cohn JS, McNamara JR, Cohn SD, Ordovas JM, Schaefer EJ. Postprandial plasma lipoprotein changes in human subjects of different ages. J Lipid Res. 1988;29:469-479.

13. Sharrett AR, Heiss G, Chambless LE, et al. Metabolic and lifestyle determinants of postprandial lipemia differ from those of fasting triglycerides. The Atherosclerosis Risk in Communities (ARIC) study. Arterioscler Thromb Vasc Biol. 2001;21:275-281.

14. Rifai N, Dufour DR, Cooper GR. Preanalytical variations in lipid, lipoprotein, and apolipoprotein testing. In Rifai N, Warnick GR, Dominiczak MH, eds. Handbook of Lipoprotein Testing. 2nd ed. Washington, DC: AACC Press; 2000:161-188.

Answer 2

There is no supporting evidence that the fasting blood specimen must come from an early morning draw. A draw in the afternoon is just as reliable. The diurnal variation in total cholesterol is small. It is estimated to be about 2.5%. (1) The exception to this rule is if the lipid abnormality is reflected in triglycerides (i.e., triglyceride-rich lipoproteins like VLDL). (2) The diurnal variation in fasting triglycerides can be rather large (i.e., 25%). It can be even larger in poorly controlled diabetics. Thus, the variations in VLDL can be large. (3,4)

All lipoproteins contain cholesterol, phospholipids, triglycerides, and apoproteins to maintain structural integrity. As the number of VLDL particles increases due to elevated triglycerides, so will the cholesterol concentration. For most patients, however, the variations in lipids (especially total cholesterol, LDL cholesterol, and HDL cholesterol) are rather small throughout the day. (5) In a clinical setting, patients in general, and diabetic and geriatric patients on medication in particular, do not like to be drawn in the afternoon because the overnight fasting times are too long and hunger pangs set in.

--Herbert K. Naito, PhD, MBA 

Chief, Ancillary Testing and Satellite Facilities

Louis Stokes Cleveland VA Medical Center

Cleveland, OH

References

1. Demacker PN, Schade RW, Jansen RT, Van't Laar A. Intra-individual variation of serum cholesterol, triglycerides, and high density lipoprotein cholesterol in normal humans. Atherosclerosis. 1982;45:259-266.

2. Cooper GR, Myers GL, Smith SJ, Sampson EJ. Standardization of lipid, lipoprotein, and apolipoprotein measurements. Clin Chem. 1988;34(8B):B95-B105.

3. Cooper GR, Myers GL, Smith SJ, Schlant RC. Blood lipid measurements. Variations and practical utility. JAMA. 1992;267:1652-1660.

4. Naito HK. Problems associated with lipid and lipoprotein analyses. In: Widhalm K, Naito HK, eds. Detection and Treatment of Lipid and Lipoprotein Disorders of Childhood. New York, NY: Alan R. Liss Inc.; 1985:19-61.

5. Mayer KH, Stamler J, Dyer AR, Stamler R, Berkson D. Epidemiologic findings on the relationship of time of day and time since last meal to five clinical variables: serum cholesterol, hematocrit, systolic and diastolic blood pressure, and heart rate. Prev Med. 1978;7:22-27.

Daniel M. Baer, MD, is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLO's editorial advisory board.

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Edited by Daniel M. Baer, MD

MLO's "Tips from the Clinical Experts" provides practical, up-to-date solutions to readers' technical and clinical issues from a panel of experts in various fields. Readers may send questions to Dan Baer by e-mail at [e-mail].