Screening techniques are a real problem if their false positive rate is high. Any significant increase in the work up rate will be a real burden on the health system (so you had better see a corresponding benefit). Worse, gold standard for follow up is going to vary by disease and location, but if it is say a biopsy and you are screening a large population you are often going to start killing people without the disease. Not many, of course, but you have to balance that against the putative improvements.