Clinical and Laboratory Standards Institute C38—Control of Preexamination Variation in Trace Element Determinations
is intended for persons responsible for the collection and processing of samples used for trace, toxic, and essential
metal and metalloid determinations. The guideline covers patient preparation, as well as considerations for collection,
transport, and processing of specimens by element. Contamination control and quality assurance programs are also
discussed.

This guideline replaces CLSI C38-A, published in 1997. Several changes were made in this edition, including: 

• Adding information on indications, patient preparations, sample selection, transport and storage, reference intervals, and conversion factors for each element 

• Updating population reference intervals from the latest US National Health and Nutrition Examination Survey for most elements 

• Adding a chapter on analytical instrumentation, recommended reporting units (see Appendix C) and an extensive appendix on reference interval studies (see Appendix D)

C38 provides guidance for preexamination considerations for trace element analysis in biological matrixes (ie, body fluids, such as whole blood, urine, hair, nails, human milk, and tissues). This guidance includes applicable recommendations for patient preparation (such as diurnal variation, diet, medications including chelation therapy and mineral supplements; the use of alcohol and tobacco; time of collection relative to the above activities, including workplace schedules, and homeostasis), specimen collection (most appropriate specimen matrix for screening, diagnosis, or monitoring), use of anticoagulants and/or preservatives; good practices for collection procedures (including containers and devices), transport requirements, contamination monitoring and control (including water, reagents, and examination consumables), and specimen processing. Specific reference is made to those elements that are known to be essential or toxic for humans and are therefore likely to be measured for clinical reasons. 

This guideline will benefit those in the medical, public health, and environmental laboratories as well as manufacturers and regulatory and accreditation agencies. 

This guideline will not include an extensive review of examination protocols and postexamination considerations, lead (Pb) testing (see CLSI C40) or content that is not consistent with current practices and guidelines.