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INTRODUCTION

Laboratory tests provide valuable information necessary to evaluate a patient’s condition and to monitor recommended treatment. Chemistry and hematology test results are compared with those of healthy individuals or those undergoing similar therapeutic treatment to determine clinical status and progress. In the past, the term normal ranges conveyed some ambiguity because, statistically, the term normal also implied a specific (Gaussian or normal) distribution and, epidemiologically, it implied the state of the majority, which is not necessarily the desirable or targeted population. This is most apparent in cholesterol levels, where values greater than 200 mg/dL are common but not desirable. Use of the term reference range or reference interval is therefore recommended by the International Federation of Clinical Chemistry (IFCC) and the Clinical and Laboratory Standards Institute (CLSI) to indicate that the values relate to a reference population and clinical condition.

Reference ranges are established for a specific age, biological sex, and level of sexual maturity; they are also defined for dietary restrictions, a specific pharmacologic status, and stimulation protocol. Similarly, diurnal variation is a factor, as is degree of obesity. Some reference ranges are particularly meaningful when combined with other test results (eg, parathyroid hormone and calcium) or when an entire set of substances being measured by clinical tests, commonly termed analytes, is evaluated.

Laboratory tests are becoming more specific and measure much lower concentrations than ever before. Therefore, reference ranges should reflect the analytical procedure as well as reagents and instrumentation used for a specific analysis. As test methodology continues to evolve, reference ranges are modified and updated.

CHALLENGES IN DETERMINING & INTERPRETING PEDIATRIC REFERENCE INTERVALS

The establishment of reference ranges is a complex process. However, the pediatric environment is particularly challenging for reference interval determination since growth and developmental stages do not have distinct and finite boundaries by which test results can be tabulated. Reference ranges may overlap and, in many cases, complicate diagnosis and treatment. Additionally, ethical concerns may exist related to blood draws in infants and young children to establish these reference ranges. A particular difficulty also lies in establishing pediatric reference ranges for analytes whose levels are changed under scheduled stimulation conditions. The common glucose tolerance test is such an example, but more complex endocrinology tests require skill and extensive experience to interpret in pediatric populations. Reference ranges for these serial tests are established over a long period of time and are not easily transferable between test methodologies. Despite these challenges, there have been multicenter studies to improve the quality and availability of pediatric reference ranges for laboratory testing. These efforts are important as clinical test instrument manufacturers routinely conduct large studies to identify reference intervals, but often focus on adult populations.

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Adeli  K: Special issue on laboratory reference intervals. eJIFCC. September 2008. http://www.ifcc.org/PDF/190201200801.pdf.
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C28A3: Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory: Approved ...

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