Clinical and Laboratory Standards Institute guideline C49—Analysis of Body Fluids in Clinical Chemistry provides guidance to the medical laboratory for evaluating measurement procedures, as well as a strategy to characterize assay performance, when applied to body fluid matrixes. Key concepts that apply to the entire test cycle, including preexamination, examination, and postexamination phases of body fluid testing are discussed. This guideline does not consider serum, plasma, whole blood, or fluids for which measurement procedures typically have performance claims in the measurement procedure documentation. Appendix A provides didactic content on the anatomy, physiology, and pathophysiology of fluid accumulation. Appendix B provides the medical rationale for quantifying measurands in body fluids and the interpretation of results in the context of disease. Appendix C provides the user with a quick reference guide to the suggested utility of fluid and measurand combinations.

This guideline replaces the previous edition of the approved guideline, C49-A, published in April 2007. This second edition of C49 provides medical laboratories with a strategy to evaluate method performance, as well as guidance on which measurands have clinical relevance when measured in body fluid matrixes. Several changes were made in this edition, including: 

• Providing medical laboratories with a workflow that: 

– Outlines important preexamination conditions to consider when validating and performing body fluid testing (see Chapter 3) 

– Discusses key concepts for body fluid matrix considerations and measurement procedure selection (see Chapter 4) 

– Offers strategies for developing a measurement procedure validation plan to provide meaningful and accurate results for appropriate and timely patient management (see Chapter 5) 

– Offers recommendations for reporting body fluid tests to aid in the diagnostic interpretation of results (see Chapter 6) 

– Covers general laboratory QA activities to support ongoing body fluid testing (see Chapter 7) 

• Assisting laboratories in minimizing patient risk and maximizing diagnostic return by: 

– Providing general information related to body fluid composition and pathogenic processes that lead to accumulation of body fluids (see Appendix A) 

– Defining the measurands and their expected concentrations that have diagnostic utility when measured in body fluids (see Appendix B)

C49 provides guidance to medical laboratories for the appropriate application of measurement procedures for body fluid testing and for reporting results. This guideline primarily focuses on the recommended practice for verification of measurement procedures for measurands in body fluids and is applicable for laboratory testing requests on body fluids that do not have performance claims in the manufacturer’s package insert or an equivalent validated laboratory-developed test. C49 does not cover serum, plasma, whole blood, urine, or fluids (eg, CSF) for which measurement procedures typically have performance claims in the manufacturer’s package insert.