#Istat chem 8 normal values verification#
Recent concepts for quality management systems require that laboratories pay more attention to identification and verification of reference limits.
However, most RLs varied significantly among laboratories, thus supporting the "old" plea for intra-laboratory RLs.Īccurate results for quantitative procedures can be useless if the reference limits for the interpretation of laboratory results are unreliable. Retrospective RLs derived from intra-laboratory data pools for the catalytic activity concentration of enzymes using a modified procedure plausibly agreed with published consensus values. Creatine kinase MB (CK-MB) values were not stratified owing to the low number of data available. For gamma-GT, further stratification for age in decades was necessary for males. Age stratification was only tested for two groups (18-49 and >or=50 years) and was significant for AST (females only), gamma-GT and lipase, not significant for amylase and inconsistent for AP, LDH and ALT. Gender stratification was necessary for alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutymaltransferse (gamma-GT), not significant for lipase and amylase and inconsistent among the laboratories for alkaline phosphatase (AP) and lactate dehydrogenase (LDH). Differences between laboratories were small but significant. The RLs obtained were similar to recently published consensus values. The model was applied to catalytic activity concentrations of several enzymes with data from different laboratories. The intersection point of the D(nd) and D(d) curves identified the RL with the highest diagnostic efficiency. The density function of the diseased subgroup (D(d)) was calculated by subtracting the non-diseased density function from D(mix) (D(d)=D(mix)-D(nd)). Percentiles were calculated to obtain retrospective RLs. This normal distribution was now considered the distribution of the non-diseased subgroup (D(nd)). It was assumed that the "central" part of the distribution represents the non-diseased population, which was defined and used to estimate a Gaussian distribution of either the original values or Box-Cox transformed data. In the current study, a bimodal method was developed to derive RLs from data stored in a laboratory information system without any assumption concerning the distribution of the diseased subgroup.Ī smoothed kernel density function (D(mix)) was estimated for the distribution of combined data for non-diseased and diseased adult subjects. The current recommendations for establishing intra-laboratory reference limits (RLs) cannot be fulfilled by most laboratories because of the expense involved. The field has evolved largely as the result of constructive international teamwork.
New developments such as reference changes are mentioned. The importance of using correct terminology, taking into consideration the aim of ordering the laboratory test and some neglected procedures (e.g., survival values) are emphasised. Subsequently international, regional and national societies established expert panels which produced recommendations covering the general principles and terminology of reference values, the concept of health, standardised specimen collection and preanalytical factors, statistical treatment of collected values, stratification of data, relating observed (patient) values to reference values, etc. Briefly, clinical measurements should be interpreted against values from proper control subjects. Saris a new concept of reference values was launched at a congress in 1969. The generally unrecognised phenomenon that laboratory results of the population tended to be lognormal instead of Gaussian attracted the attention of the author, who became sceptical of the concept of normal values because of its ambiguity. This manuscript reviews the introduction of the concept of reference values, the corresponding philosophy, and subsequent recommendations reflecting the different subtopics of the field.
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