There is a good review of methods of evaluating the status of trace elements in the body for Nutrition
Ed Fairweather-Tait and Harvey
Micronutrients status methods Proceedings of the EURRECA Workshop and working party on new approaches for measuring micronutrient status.
BJN vol 99 Supplement 3 pp S1-80

Biomarkers of copper status: a brief update
Harvey and McArdle
Copper (Cu) deficiency in humans is associated with anaemia, hypercholes-terolaemia and bone malformations. Despite significant effort over several decades a sensitive and specific Cu status biomarker has yet to be identified.
Current biomarkers include a range of cuproenzymes such as the acute phase protein caeruloplasmin and Cu-Zn-super-oxide dismutase all of which are influenced by a range of other dietary and environmental factors. A recent development is the identification of’ the Cu chaperone, CCS as a potential biomarker; although its reliability has yet to be established.
Merhods to assess iron and iodine status
Zimmermann
Four methods are recommended for assessment of iodine nutrition: urinary iodine concentration,1 the goitre rate, and blood concentrations of thy¬roid stimulating hormone and thyroglobulin. These indicators are complementary, in that urinary iodine is a sensitive indicator of recent iodine intake (days) and thyroglobulin shows an intermediate response (weeks to months), whereas changes in the goitre rate reflect long-term iodine nutrition (months to years). Spot urinary iodine concentrations are highly variable from day-to-day and should not be used to classify iodine status of individuals. International reference, criteria for thyroid volume in children have recently been published and can be used for identifying even small goitres using thyroid ultrasound. Recent development of a dried blood spot thyroglobulin assay makes sample collection practical even in remote areas.
Serum ferritin remains the best indicator of iron stores in the absence of inflammation. Measures of iron-deficient erythropoiesis include transferrin iron saturation and erythrocyte zinc protopor-phyrin, but these often do not distinguish anaemia due to iron deficiency from the anaemia of chronic disease. The serum transferrin receptor is useful in this setting, but the assay requires standardization. In the absence of inflammation, a sensitive method to assess iron status is to combine the use of serum ferritin as a measure of iron stores and the serum transferrin receptor as a measure of tissue iron deficiency.

Update on the assessment of magnesium statue
Arnaud
There is no simple rapid and accurate method, only serum magnesium and use of loading dosage methods.

Indicators of zinc status at the p[population level: a review of the evidence.
Gibson, Hess, Hotz, Brown

There are few reliable methods, only serum zinc and the clinical sign of clinical runting in children. of

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