When to Use A or An Before Acronyms

Today’s lesson is a quick tip about how to choose the correct article (a/an, called “indefinite articles”) before an acronym. These articles are occasionally swapped, and it’s easy to see why! Choosing the article may seem simple based on whether the acronym stars with a consonant or vowel, but usage depends on how the subsequent word is pronounced, not spelled.

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What does this mean?

The patient underwent a/an MRI scan.

When we see MRI written, we mentally say each letter—em are eye—rather than “magnetic resonance imaging.” Which article should it get?

Since the letter M is pronounced starting with a vowel (em), we use the article that goes with vowel sounds: an.

The patient underwent an MRI scan.

And what if we didn’t use the acronym but wrote the term out?

The patient underwent a magnetic resonance imaging scan.

This time, the subsequent word (magnetic) starts with a consonant sound, so we use “a.” Make sense?

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Here are some other examples:

a nurse practitioner certification exam / an NP certification exam

a STEMI / an ST elevation myocardial infarction

a nonsteroidal anti-inflammatory drug / an NSAID

You get the idea!

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If you’re stuck with figuring out what article to use before an acronym (or any word), just say it out loud. Its pronunciation determines which article it receives—nice and straightforward.