when should i suspect my cholesterol test is wrong

According to the Clinical Practice Guidelines developed by the U.S. Department of Veterans Affairs, healthcare decisions should not be made until an individual has had two cholesterol tests.

Between one and eight weeks should separate each blood test. If the results of the two tests vary by 30 mg/dL or more, something may well be amiss and the tests should be repeated.

The most common underlying reason for surprising cholesterol lab results is a temporary change in your body’s chemistry. Here are some examples of how and why your cholesterol results could temporarily be less than an accurate mirror of what is usually going on in your body:

A recent cardiac event, such as a heart attack or stroke, can temporarily lower lipid levels.
Surgeries and infections can also temporarily lower your cholesterol levels.
Certain medications, such as corticosteroids and estrogens, can raise your lipid levels. Ask your doctor for a full list of medications that might affect your test results. Make sure you are clear about how long you need to be off a given medication to ensure accurate results.

Pregnancy can increase cholesterol levels, so a cholesterol test should not be considered reliable until a woman is about 4 months postpartum.
When cholesterol is tested as part of a lipid profile, you will be instructed to fast with only water for 9-12 hours before your blood is drawn. If you are unable to fast prior to your cholesterol test, tell your doctor. And if you had a slip-up and consumed something prior to your test, let your doctor know. Food in your system can alter your cholesterol levels.
Alcohol consumption can also affect your test results. Most experts agree that you should avoid any alcoholic beverages for 24 hours prior to testing.
Human error can also affect your test. It’s uncommon, but lab mistakes and reporting mistakes do happen. Make sure that the person drawing your blood asks for your identification, and then labels the tubes with your information. There are other ways that laboratory errors happen, but misidentification is one you can help prevent.