More testing is not better testing. Most micronutrient markers move slowly, so the useful question is which numbers change fast enough to be worth watching.
A realistic cadence
Twice a year: vitamin D (25-OH-D) and ferritin. Vitamin D swings seasonally - a level that looks fine in September can be depleted by March. Ferritin responds to training load, diet shifts and, for women, menstruation.
Once a year: B12, folate, zinc, a standard metabolic panel. These drift over months, not weeks.
After a change: re-test the specific marker eight to twelve weeks after you start supplementing it. Earlier than that you are mostly measuring noise - red blood cells turn over on a roughly 120-day cycle.
Reading the results
Lab reference ranges flag disease, not performance. 30 ng/mL of vitamin D clears the deficiency bar, while most research on energy and immunity clusters benefits around 40-60 ng/mL. Ferritin of 20 is technically normal and still consistent with heavy legs and flat training.
This is why the blood-based plans tune doses to your actual numbers and re-check on a schedule - it turns supplementation from a guess into a feedback loop.