I see at least 1 syntax error
var rpt = new LabReport()
{
ref_id = "" + count, <===== ref_id is defined as an int. This won't work
t_name=e.lab_test.t_name,
result=sublist
};
Also if your classes of LabReport and LabSubReport are entities within Entity Framework and ref_id is supposed to be a Foreign Key, you might try adding the decorator for the Foreign Key to prevent LabSubReport from generating a ref_id when it's constructed.
public class LabSubReport
{
[ForeignKey("ref_id")]
public int ref_id { get; set; }
public String l_test { get; set; }
public String t_value { get; set; }
}