It’s an HDL. The abbreviation HDL is typically pronounced as individual letters. Since the first letter, the h, starts with a vowel sound (aich), it takes the article "an".

It’s an HDL. The abbreviation HDL (High-Density Lipoprotein) is typically pronounced as individual letters. Since the first letter, the h, starts with a vowel sound (eich), it takes the article "an".

Experts usually recommend an HDL level of 60 milligrams per deciliter or above.

Experts usually recommend a HDL level of 60 milligrams per deciliter or above.

Remember, the rule for using "a" or "an" is based on the initial sound of the following word, and not on how it's spelled.

An HDL cholesterol particle takes the lipids and cholesterol to the liver for excretion or destruction.

Similarly, we say "an LDL level" (not "a LDL level").

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

Follow the same convention with other characters and abbreviations that start with H and are pronounced as separate letters. For example, we say: an H, an HDMI cable, an HIV test, an HPV infection, an HDD (a Hard Disk Drive), an HTML document, or an HTTP server.

I need to buy an HDMI cable.