Sometimes hyphenated compound words become so well established that the hyphen is dropped and the words are joined together without a hyphen. When such a word can be used either as a noun, adjective, or verb, the noun and adjective forms are joined without a hyphen, but the verb form remains two separate words if one of them is a preposition.
noun or adjective verb
checkup check up
followup follow up
workup work up
followthrough follow through
The patient was lost to followup (noun).
Followup exam will be in 3 weeks (adjective with a noun following)
I will follow up with the patient in 2 weeks (verb)
I will work up her symptoms with a CT scan.
Her workup revealed no abnormalities.
Diane Gilmore, CMT, AHDI-F
Director of Education/Instructor