Follow up versus followup

I cannot say how many times I have mixed up these two words while typing my medical reports.  I have finally found a way to tell which word I should actually be using, and I wanted to pass along this trick because I think it is an awesome way to understand which form of the word to use.

followup is a noun (adj)
follow up is a verb

Here is the trick.  Since follow up (2 words) is a verb, exchange out follow up for another verb and see if it still makes sense.  Substitute eat for follow up.  If you cannot substitute another verb then you use the combined word form followup.

The first example, the form should be the combined word form, followup because if you substitute the verb, it does not make sense.

Example 1:  The patient will have home health followup for more......
                  The patient will have home health eat for more......

Now lets try it with a sentence that you can substitute the verb with.

Example 2:  The patient will follow up on Tuesday.
                    The patient will eat on Tuesday.
                 
 Example 3:  We are going to follow up her tumor.....
                     We are going to eat her tumor........
Now that is a little gross but I just wanted to make my point.

I wish I had known about this sooner but now that I do, I never get the words mixed up.