How to Prepare for an Apolipoprotein B Test: The Rules
Apolipoprotein B, usually shortened to apoB, is increasingly recommended as a sharper measure of cardiovascular risk than LDL cholesterol alone. Good news for anyone booking the test: it is one of the more forgiving blood tests to prepare for. Still, a few simple rules make the result more reliable and comparable over time.
What apoB measures and why it matters
Every LDL, VLDL, IDL and lipoprotein(a) particle carries exactly one apoB molecule on its surface. Measuring apoB is therefore effectively a count of the particles capable of entering the artery wall and contributing to plaque.
LDL cholesterol measures how much cholesterol those particles carry, not how many particles there are. Usually the two track closely. In people with insulin resistance, high triglycerides, type 2 diabetes or obesity, however, LDL particles tend to be smaller and more numerous, so LDL cholesterol can underestimate risk.
Sniderman and colleagues summarised the evidence that apoB is a more accurate marker of atherogenic risk than LDL cholesterol or non-HDL cholesterol in such cases. The 2019 ESC/EAS dyslipidaemia guidelines recommend apoB for risk assessment, particularly in people with high triglycerides, diabetes, obesity or very low LDL cholesterol.
In the UK apoB is not part of the standard NHS lipid profile, but it can be requested by a clinician and is widely offered in private testing. Knowing how to prepare helps make sure the money and the needle are not wasted.
Do you need to fast?
The short answer is no, not usually. A joint consensus statement from the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine (Nordestgaard and colleagues, 2016) concluded that fasting is not routinely required for lipid profiles. ApoB changes very little after a typical meal.
Triglycerides are the component most affected by eating, rising for several hours after a fatty meal. Since apoB reflects particle number rather than triglyceride content, it is relatively stable. That makes it attractive for people who find fasting difficult, including athletes training early in the morning.
There are exceptions. If your previous non-fasting triglycerides were very high, or the test is part of an investigation for pancreatitis or a genetic lipid disorder, your clinician may still ask you to fast for 8–12 hours. In that case, water is allowed and should be drunk normally.
A practical compromise for most people is a normal, moderate breakfast rather than either a full fast or a very fatty fry-up. Whatever you choose, doing the same thing before each repeat test improves comparability.
Training, alcohol and lifestyle before the test
Hard exercise can temporarily alter blood lipids and plasma volume. Long endurance sessions dilute the blood slightly over the following day, and very intense sessions can shift values in either direction. The effect on apoB is modest, but it adds unnecessary noise.
The following checklist works well for most people:
- Avoid unusually long or intense training for 24–48 hours before the sample.
- Avoid alcohol for at least 24 hours; heavy drinking raises triglycerides and can affect particle composition.
- Do not change your diet dramatically in the week before the test; the aim is to measure your usual state.
- Drink water normally and arrive well hydrated.
- Sit quietly for a few minutes before the sample is taken.
A recent large change in body weight, for example during a contest preparation diet or a bulking phase, can alter lipids substantially. It is usually better to test during a period of stable weight to understand your baseline.
Smoking or vaping immediately before the test should also be avoided, as nicotine affects the circulation and may make venepuncture harder.
Illness, medicines and supplements
Acute illness, infection, surgery or a heart attack can lower lipid levels for several weeks. If you have been unwell recently, it is better to postpone a routine apoB test until you have recovered fully, unless your clinician says otherwise.
| Factor | Possible effect on apoB | What to do |
|---|---|---|
| Normal breakfast | Minimal | Acceptable unless told to fast |
| Heavy alcohol the night before | Can alter lipids | Avoid for 24 h or more |
| Recent infection or surgery | Temporary reduction | Wait several weeks after recovery |
| Starting a statin or ezetimibe | Reduction expected | Retest after 4–12 weeks as advised |
| Anabolic steroid use | Adverse lipid changes | Disclose to the clinician |
| Pregnancy | Physiological rise | Interpret with obstetric context |
Do not stop lipid-lowering medicines before the test unless instructed. Your clinician generally wants to see how well treatment is working, not what your levels would be without it.
Some medicines raise apoB, including certain retinoids, some antipsychotics, corticosteroids and some HIV medicines. Androgens, including anabolic steroids, typically lower HDL cholesterol and may raise LDL and apoB. Mentioning all medicines and substances you take helps the clinician interpret the result correctly.
Supplements such as plant sterols, psyllium, red yeast rice and high-dose fish oil can influence lipids. They do not need to be stopped before testing, but it is useful to note them on the request.
After the test: reading and repeating it
ApoB is usually reported in grams per litre (g/L) in the UK. Target values depend on your overall cardiovascular risk. European guidelines suggest lower targets for people at high and very high risk, and a clinician will compare your result with the appropriate goal.
Biological variability means a single result can differ from the "true" average by a small amount. If a decision depends on the value, a repeat test under similar conditions is reasonable.
After starting or changing lipid-lowering treatment, a repeat measurement is typically taken after a few weeks to a few months. Thereafter, annual testing is common in stable patients.
Ference and colleagues, writing for the European Atherosclerosis Society, described the cumulative nature of exposure to apoB-containing particles: the longer and higher the exposure, the greater the risk. That is why early testing and lifestyle changes in young adults with high values can have lasting benefits.
Conclusions of the editorial team
ApoB counts the particles that cause atherosclerosis and is especially useful for people with high triglycerides, diabetes or obesity.
Fasting is generally unnecessary, but avoiding alcohol, hard training and acute illness before the test helps produce a reliable, repeatable result.
Consistency is the golden rule: the same time of day, similar meals and similar training before each sample. Related articles on our site cover atorvastatin trials, ezetimibe interactions, and the FSH test for athletes.
References
- Sniderman AD, Thanassoulis G, Glavinovic T, et al. Apolipoprotein B particles and cardiovascular disease: a narrative review. JAMA Cardiol. 2019;4(12):1287–1295.
- Mach F, Baigent C, Catapano AL, et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk. Eur Heart J. 2020;41(1):111–188.
- Nordestgaard BG, Langsted A, Mora S, et al. Fasting is not routinely required for determination of a lipid profile: clinical and laboratory implications including flagging at desirable concentration cut-points—a joint consensus statement from the European Atherosclerosis Society and European Federation of Clinical Chemistry and Laboratory Medicine. Eur Heart J. 2016;37(25):1944–1958.
- Ference BA, Ginsberg HN, Graham I, et al. Low-density lipoproteins cause atherosclerotic cardiovascular disease. 1. Evidence from genetic, epidemiologic, and clinical studies. A consensus statement from the European Atherosclerosis Society Consensus Panel. Eur Heart J. 2017;38(32):2459–2472.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
