Conservation du tube primaire sur le site de dialyse en vue du dosage différé de la PTH : quels tubes ? Quelle température ?

Influence of exogenous and endogenous factors on the quality of the preanalytical stage of laboratory tests (review of literature)

A literature review in the article presents an analysis of the influence of endogenous and exogenous factors on quality of preanalytical phase of laboratory testing. The review shows significance of external and internal factors influencing blood samples at preanalytical phase of laboratory testing. Among the exogenous factors considered: phlebotomy, test tubes for samples, transportation and storage. A number of factors exist at this phase that significantly affect test results. We examined these aspects of phlebotomy process: staff training, disinfectant contamination, needle diameter, needle material contamination. The review considers possible contamination with tube components and the importance of choosing the right anticoagulants and excipients. Transportation and storage of biological samples can be a source of errors at the preanalytical phase of laboratory testing. We analyzed the problem of determining the stability of analytes during storage and aspects of transportation samples by modern means. Among the endogenous factors considered: hemolysis, lipemia, icterricity, cell metabolism.. Hemolysis is one of the most frequent consequences of errors at the preanalytical phase. We analyzed importance of choosing a method for identifying hemolized tubes and the heterogeneity of bias results on different analytical systems. The review shows contribution of various classes of lipoproteins to turbidity of sample, possible preanalytical errors and impact on analytical tests. We examined possible effects of high bilirubin concentrations on analyte measurements. In the review, we also examined metabolism of some cells and its effect on samples.

Evaluating sample stability in the clinical laboratory with the help of linear and non-linear regression analysis

As it is common practice for laboratories to store patient samples for a predefined period, allowing clinicians to request additional tests on previously collected samples, knowledge about sample stability is indispensable for the laboratorian. A common approach to estimating the maximum storage time is to use a discrete study design, measuring the analyte of interest at various time-points and then checking for significant differences with the help of a statistical test, such as Student's t-test, Wilcoxon's test or an analysis of variance (ANOVA) test. Because only discrete time intervals are considered, stability data can just be approximated. Alternatively, a continuous study design, as described by the Clinical and Laboratory Standards Institute (CLSI) for performing stability experiments for in vitro diagnostic reagents, can also be adopted by the clinical laboratory to evaluate the stability of biological samples. The major advantage of this approach is that it allows laboratories to define individual stability limits for different medical situations and offers more flexibility when choosing time-points for measurements. The intent of this paper is to demonstrate the evaluation of sample stability in the clinical laboratory with a continuous study design implemented with linear or non-linear regression analysis. Appropriate statistical modeling and acceptance criteria are presented, stability functions are described briefly, and checking the overall validity of the results is discussed.

Stability study of 81 analytes in human whole blood, in serum and in plasma

OBJECTIVE

We studied the pre-analytical stability of 81 analytes based on the variables of delay before processing, storage as whole blood or serum/plasma, the storage temperature and the type of tube the sample was stored in.

DESIGN AND METHODS

The mean difference between assays for samples from 10 subjects was calculated with the samples being kept under different storage conditions and for different times between sampling time and analysis: up to 24h for biochemistry, coagulation and hematology, and up to 72 h for hormonology. This difference was compared to the acceptable limits derived from the analytical and the intra individual biological variation.

RESULTS

Most of the analytes investigated remained stable up to 24h under all storage conditions prior to centrifugation. However, some analytes were significantly affected either by delay, tube type or temperature, such as potassium, inorganic phosphorus, magnesium, LD, glucose, lactate, mean corpuscular volume, mean corpuscular hemoglobin, activated partial thromboplastin time, insulin, C-peptide, PTH, osteocalcin, C-telopeptide and ACTH.

CONCLUSION

This study may be useful to help define acceptable delay times and storage conditions when a short time between sample collection and processing is not possible.