By 'scrolling between items' items i suppose you mean the different tests. It was my first impression that this could be confusing. If I understand correctly it is the users task is to input those test rather than have an overview over them in detail.
Since a user will only input one test at a time it might not be necessary to have them all in one scrollable view. Also having a modal for each field is not very efficient since the user has to tap on the field, enter the text then close the modal and tap on the next field.
So what I would suggest is to have a list of the tests. A tap on one test opens the whole form for this test. In the modal all fields are editable and the user can jump to the next field using 'Enter' on the keyboard after each field. For the severity I might provide a choice of given severities. Depending on the amount of severities this could be done with a segmented control.
Test detail -form
As always: test those solutions with actual users. Only this way you will see which solution is the most efficient and usable for your users.