Yes, it is considered three articles. The comma after the second to last article in the list is considered optional, but most people use it for clarity. For example, the following is correct also:
I have ordered a complete blood count, a pap smear and a lipid panel.
The problem with this is the reader may not know whether the pap smear and a lipid panel are together considered one article (together are "one thing"). To eliminate confusion, it is always best to use commas after the second to last article, except if there are just two articles in total. For example, you wouldn't use a comma in this case:
I own a dog, and a cat
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