It’s an LDL. Because the initial letter of the abbreviation LDL (High-Density Lipoprotein) has a vowel sound (an L), we use the indefinite article "an".

It’s an LDL. Because the initial letter of the abbreviation LDL (High-Density Lipoprotein) has a vowel sound (an L), we use the indefinite article "an".

You should study the structure and composition of an LDL particle.

You should study the structure and composition of a LDL particle.

Keep in mind that LDL is usually pronounced as individual letters, and the rule for using a or an is based on pronunciation (not spelling). Consequently, the abbreviation LDL takes the article "an".

Doctors generally recommend an LDL level below 70 mg/dl.

An LDL cholesterol test can be used to check the amount of LDL cholesterol in your blood.

Follow the same convention with the acronym HDL (High-Density Lipoprotein) and other abbreviations that start with a vowel sound. For example, we say an L-shaped building, an LGBT group, etc.

The average American man has an HDL level of about 42.

I have an L-shaped room that is too small.