According to the Dietary Reference Intake review, neither plasma nor urine concentrations can serve as useful clinical indicators of<unk>  status. Before<unk>  became a standard ingredient in total parenteral nutrition (TPN), people getting TPN as their sole source of nutrition developed symptoms that were reversed within two-week after<unk>  was added.
Chromium deficiency
Fluorine deficiency
Boron deficiency 
Biotin deficiency
Metal toxicity
Lead poisoning
Fluoride toxicity
Selenium deficiency