How often should you get your blood tested for metal posioning ?

2 of my old bf's had rods. They never got them checked so I never thought of checking into that. I looked it up now that you ask and this is what I found. I didn't see how often but I do see there are lawsuits. What did your doctors tell you about how often?
https://www.google.com/search?q=metal+poisoning+from+hip+replacement&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb