Indefinite articles for abbreviations

Have you ever found yourself wondering whether a particular abbreviation is to be preceded by 𝗮/𝗮𝗻?

The trick

Use your ears (how it's pronounced ), instead of your eyes (NOT, how it's spelled)?

e.g. 𝗔 HIV patient

e.g. 𝗔𝗻 HIV patient

The abbreviation HIV begins with the consonant 'H', but here the pronunciation 'aitch eye vee' is to be considered; therefore '𝗮𝗻' should precede the abbreviation.