indefinite article with initialisms

Match a or an to the first sound you speak, whether you read the letters or say the form as a word. An initialism (letter by letter) takes an when the first letter’s name begins with a vowel sound: an FBI agent (eff), an MRI, an NPR report (en). It takes a when that name begins with a consonant sound: a CIA brief (see), a UFO sighting (you). An acronym (spoken as a word) follows the word’s first sound: a NASA flight (nass), a UNICEF grant (you-nuh). When both readings are current, match the one you use: an FAQ page if you say eff-ay-cue; a FAQ page if you say fack.