Learn Portuguese (Portugal): Ufa, ainda bem que o exame foi negativo! - Phew, it is a good thing that the exam was negative!

You are right that phrases expressing emotion usually trigger the subjunctive, like with que bom que. However, ainda bem que is a major exception in Portuguese. It always takes the indicative because it treats the event as a confirmed, established fact rather than a subjective feeling or possibility. Since the exam being negative is a confirmed reality, we use the normal past tense foi.

Does ainda bem que have a literal translation that makes sense?

Literally, it translates to something like 'still well that,' which does not map cleanly to English. It is best to memorize it as a fixed phrase meaning 'thank goodness that,' 'luckily,' or 'it is a good thing that.' It is the standard way to express relief about a favorable fact.

Why do we use foi (from ser) instead of esteve (from estar) for the test result? Isn't a person's health a temporary state?

While health can change, the result of a specific medical test or exam uses the verb ser. This is because the outcome of that exact test is a permanent, definitive classification of that specific event. That particular piece of paper or lab result will always be negative, so we use ser.

Is ufa a real word people say, or just a written sound effect?

Ufa is a very common and genuine interjection in spoken Portuguese. It is the direct equivalent of the English 'phew,' used exactly like it is here to express relief, exhaustion, or escaping a close call.