Just from quickly skimming the literature, it looks like you can measure it in vivo with X-ray fluorescence. Getting access to one of those would be hard, but y

Just from quickly skimming the literature, it looks like you can measure it in vivo with X-ray fluorescence. Getting access to one of those would be hard, but you might be able to persuade a researcher to use you in a trial? I imagine you've already looked into this a fair bit. Are you on medication to help with the (diagnosed) bipolar disorder? Do you find that e.g. lithium eases your symptoms? If so, I'd be inclined to think you're bipolar -- irrespective of whether you also have low-level lead poisoning.