Can you think of any reason why blood cultures would come back with negative results within 2 hours even though antibiotics not commenced until hours after the results have come back.

Yes: IT HAPPENS ALL THE TIME! Since many infectious agents circulate in the blood at certain INTERVALS between which no organism can be detected! That is why MULTIPLE Blood Cultures are taken instead of ONE SAMPLE! Hope this helps! Dr Z

Unclear question: If the blood culture results were reported within 2 hours, then it could not have bee culture, as that takes at least 24 hours, longer depending on the type of organism and microbial load. It was probably some other test like CRP, not blood culture, that was reported within two hours of blood collection. It may help to talk to the pathologist in-charge of the laboratory.