I too required the same thing as yours and came out with a solution. Think it may solve your purpose..
1.Create a Calculated Field with any name (Say MedRecord )and give
str([MedRecNum]) + ' - ' + str([PtAdmitDate]) + ' - ' + str([PtDischDate])
in formula field.
2. Create another Calculated Field with Name Count_MedicalRecord and use COUNTD() to count the previous calculated field... as
(Keep this in formula field)
ant this Count_MedicalRecord will give you the number of times the patient has visited.