It is difficult to say because it is unclear what the population here is that you base your test on, and what your data look like.
I mean: is 4 more than 3? yes. but is it significant? well, then it depends on the population you drew your 4 and 3 from, and how you determined what "4" is.
It looks like you have only 2 observations, namely number of diagnoses at T1 and T2. You cannot infer anything from 2 observations.
Or maybe you can, and you have more than 2 observations. for instance, you have 100 hospitals, each have a number of diagnosis in year 1 and year 2, and you want to see if the average number of observations differs.
But to know whether or not you can actually do anything with statistics, we need to know more about your data.