We have had a few worrisome incidents of American Foulbrood (AFB) in southern Maine this year and have found several pockets of European Foulbrood (EFB) as well. There is a different test for the different diseases. If you see cells where larvae are discolored or misshapen- before they are capped, that indicates EFB. Larval remains under sunken or perforated caps are an indication of American Foulbrood, particularly if the remains "rope" out when pulled with a toothpick.
These are great pieces of diagnostic equipment to have in your kit in case one of your hives starts to make you worry. Results in 3 minutes.