Establishment of reference intervals of some clinical chemistry analytes in an indirect mode partitioned by sampling times

The establishment of reference intervals of clinical laboratory tests performed in is not possible for all clinical laboratories. Indirect estimation of reference intervals is being popular over direct methods which are time-consuming, expensive and sometimes not feasible for resource-limited laboratories.This study tries to establish (in a indirect, nonrandom and aposteriori mode) reference intervals of total of 14 clinical chemistry analytes measured in serum specimens of patients who were in our medical center as outpatients between 2009 and 2010 years. This is the first study which describes the time of sample drawing as a subgruoping factor in establishment of reference intervals indirectly. The aim of this study is at last establishment of local reference intervals in Malatya Province with special emphasis on establishment of reference intervals partitioned with sampling time. The analytes which were incorporated in our study were having diurnal rithm ones with a total of 7 analytes and remaining ones which are not associated with diurnal rithm in scientific literature. Six of them namely serum iron, TSH, total calcium, inorganic phosphate, prolactin, and total cortizol had a significant difference between their means of different sampling times. Except for serum total calcium we determined certain reference intervals based on these sampling times (p<0,05). In addition we compared all of newly establish reference intervals with reference intervals which are originated from direct methodologies, reference books and manufacturer recommendations by using analyte-specific reference change values (RCVs). For most analytes, there were significant differerences between our reference limits and other methods?limits. But for some analytes such as TSH, total calcium, inorganic phosphate, PTH, folate, there were no significant differences between lower and upper reference limits. Our study underlines the importance of preanalytical factors in establishing reference intervals and lets us to understand that transferring reference intervals of manufacturer-based or reference book-based is not always a true reference.Currently, indirect establishment of reference intervals in clinical laboratories which has not yet accepted beyond just complemantary, confirmative, or corrective properties is not replaced with direct methods. Making indirect methods more standardized in the issues of outlier detection and subgrouping and more applicable is compulsory for future.