How to prepare for the 'Triglycerides' test: rules for taking it

Triglycerides are the main form in which the body stores and transports fat. Unlike cholesterol, their level in the blood can change several-fold within just a few hours after eating. That is precisely why the triglyceride test suffers most from improper preparation. The editorial team explains how to take it so that the result reflects your real metabolism and not last night's dinner.

Why triglycerides are so variable

Triglycerides enter the blood from two sources. The first is dietary fat: after absorption in the intestine it is packaged into chylomicrons and enters the bloodstream via the lymph. The second is the liver, which synthesizes triglycerides from excess carbohydrates and fatty acids and releases them within very-low-density lipoproteins (VLDL).

After a meal containing fat, the triglyceride concentration gradually rises, usually peaks after 3–4 hours and returns to baseline after 6–8 hours or longer, depending on the composition of the food and individual metabolism. In people with insulin resistance, obesity or hereditary disorders, the «tail» after a meal is significantly longer.

Because of these dynamics, triglycerides are the key indicator for which the «fasting or postprandial» format truly matters. The 2016 consensus of the European Atherosclerosis Society allows taking a lipid profile without fasting for general risk assessment, but separately notes that after an ordinary meal triglycerides are on average about 0.3 mmol/L higher, and after a fatty meal — significantly more.

The conclusion is simple: if triglycerides are the main purpose of the test (suspected hypertriglyceridemia, treatment monitoring, assessment of metabolic syndrome), preparation must be stricter than for routine cholesterol screening.

Fasting: how long and how to do it properly

The standard interval for a fasting test is 10–12 hours without food. A shorter interval risks capturing the «tail» of dinner, especially if it was late and fatty. On the other hand, excessively long fasting (over 14–16 hours) is also undesirable: the body ramps up lipolysis, and the values no longer reflect the usual state.

During fasting you are allowed to drink plain still water. Tea, coffee with milk, juices, smoothies, sugared chewing gum, sports drinks and BCAAs with sweeteners are better postponed until the blood draw. Black coffee without sugar formally contains no fat but can affect stress hormones, so for comparability of results we advise going without it.

It is important that not only the last dinner matters, but also the diet over the previous 2–3 days. If you abruptly «went on a diet» before the test or, on the contrary, threw a feast, you will get a result that is not characteristic of your usual regimen. The purpose of the test is to capture the typical state, not the best or the worst.

The optimal time for the draw is in the morning, roughly between 7 and 10 o'clock. People who work night shifts should agree with their doctor on the timing of the test, taking into account their own sleep and eating schedule, so that the interval without food is sufficient.

Food, alcohol and supplements

Alcohol is one of the strongest stimulators of triglyceride synthesis in the liver. Even moderate consumption the day before can raise the result, and in people prone to hypertriglyceridemia — several-fold. We advise abstaining from alcohol for at least 48–72 hours before the test.

Simple sugars, especially fructose in sweet drinks, juices and desserts, stimulate hepatic lipogenesis. A high-carbohydrate diet the day before can raise triglycerides no less than fatty food. Conversely, very low-carbohydrate eating patterns often lower them, so an abrupt change in diet before the test distorts the picture in both directions.

Regarding supplements: omega-3 fatty acids (EPA and DHA) in high doses lower triglycerides, and this effect is used in medicine. If you take them regularly — continue and inform your doctor. If you plan to assess the effect, take a follow-up test no earlier than 6–8 weeks of regular use.

Medications also matter. Triglycerides can be raised by corticosteroids, oral estrogens, retinoids, some antipsychotics, thiazide diuretics and beta-blockers; and lowered by fibrates, statins and omega-3. Prescribed drugs must not be discontinued on your own — it is enough to note them on the referral.

Training, glycerol and laboratory traps

A single intense or prolonged training session activates lipolysis and alters triglyceride metabolism over the following several hours and even for a day. Regular aerobic activity lowers triglycerides in the long term, but a separate «killer» session the day before makes the result atypical. Therefore, for 24–48 hours before the test it is better to limit yourself to light activity.

A trap specific to athletes is glycerol. Most laboratories determine triglycerides by an enzymatic method that in fact measures glycerol after the triglycerides are broken down. Free glycerol in the blood, for example after taking glycerol supplements for a «pump» or hyperhydration, can be perceived by the analyzer as triglycerides, and the result will be falsely elevated.

Another laboratory trap is lipemia. If triglycerides are very high, the serum becomes cloudy, «milky». This interferes with the optical measurement of other indicators, so sometimes the laboratory asks you to redo the blood draw after fasting. This situation is in itself already an important diagnostic finding.

Finally, acute conditions. Infections, injuries and inflammatory processes alter lipid metabolism, and triglycerides during sepsis or severe illness can rise. A routine test is better postponed until after full recovery.

How to read the result

For a fasting test, a triglyceride level below 1.7 mmol/L (150 mg/dL) is considered optimal. For a non-fasting test, the 2016 consensus proposes considering a level from 2.0 mmol/L (175 mg/dL) as elevated. That is why it is important to see on the report exactly how the blood was taken, and it is worth informing the doctor about this.

Moderately elevated triglycerides are often a marker of insulin resistance, excess calories, alcohol or a sedentary lifestyle, and are also associated with increased cardiovascular risk. Very high values, roughly above 10 mmol/L, are linked to the risk of acute pancreatitis and require urgent medical attention.

When to retake the test:

• if the non-fasting result exceeds 5 mmol/L — repeat while fasting;
• after a change in diet or the start of treatment — in 6–8 weeks;
• if the test was taken during illness or after a feast — after the regimen normalizes.

Triglycerides also affect the calculation of LDL cholesterol by the Friedewald formula. At high values the calculation becomes inaccurate, so the doctor may suggest direct LDL or determination of apolipoprotein B.

Editorial conclusions

Triglycerides are the most «capricious» indicator of the lipid profile: their level depends on the last meal, alcohol, recent workouts and even on supplements containing glycerol.

For an accurate test, follow a simple standard: 10–12 hours without food, no alcohol for 2–3 days, your usual diet and no heavy exertion the day before.

If the result is high, do not jump to conclusions — first make sure the preparation was correct, and if necessary repeat the test.

The editorial team also recommends reading our materials on preparing for the HDL and LDL test, on apolipoprotein B, and on fasting glucose as a marker of carbohydrate metabolism.

References

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