Dear Dave,
With HealthFrame you can already do that, by using a combination the User Defined Graph feature and the built-in customization support.
Please see the attached file for a sample HealthFrame personal health record with three Complete Blood Count (CBC) tests, one week apart. Please note in there are two user defined graphs that display (1) red vs. white blood count; (2) four measurements from the CBC (hemoglobin, MCH, Hematocrit level and MCV).
Thanks,
Support Team