Both things matter, and you need to consider what the follow-up test might be and what it would cost not just financially but also in terms of pain, lost time,

Both things matter, and you need to consider what the follow-up test might be and what it would cost not just financially but also in terms of pain, lost time, risk of harm and so on. There are medical tests which have such a high rate of false positives that in practice in the absence of other indications you would ignore a positive result, because the only possible follow-up test would be a non-risk-free biopsy, and therefore, for your peace of mind, it's probably better not to do the first test at all.