Is it possible that you create an object of bloodtest when you open the page and then another one in the datasource microflow?
The fact that they dissapear is because you created the objects, but never commit them. In the save microflow you retrieve the objects from the database and commit that list, however the bloodtest you just created is not in the database yet, since it hasn't been commited to the database yet.
In addition when opening the page where you fill in the bloodtest information, I would create a new bloodtest object. I would than pass the bloodtest object to the page, instead of the patientdetails.
Hope this helps!