Revista del Laboratorio Clínico最新文献

Within the analytical quality system of the clinical analysis laboratories, it is usual to calculate Total Error (ET) and Six sigma (6Sigma). The estimation of the measurement uncertainty (U) is a parameter that should be incorporated as part of the quality management, and is a requirement of ISO 15189. The U provides a range of probable values where the true value of a measurement result can be obtained, providing a quantitative value of the level of doubt for each value. The objective of this work is to evaluate the performance of 16 analytical methods using the calculation of the ET and the 6Sigma, as well as the U, based on an approximation model of the Nordtest guide. Internal (CCI) and external quality control (EQA) data were used. Quality requirements (ETa) based on CLIA and biological variability (BV) were used to evaluate the performance of the methods. The 16 methods presented acceptable performance, with the ET values obtained being lower than the proposed ETa and the 6Sigma values ≥ 3. Three methods have values of 6Sigma between 3 and 4, 2 methods between 4 and 5Sigma, five values between 5 and 6Sigma, and six had 6Sigmas greater than 6. The uncertainties associated with all measurements provide complementary information about the range of values in which the true value is found.

Introduction

Flow cytometry has shown to be useful for ruling out urinary tract infection over the last few years. Its integration into the Microbiology Laboratories could avoid the urine culture of 60% of the samples. The aim of this study is to evaluate the usefulness of flow cytometry in the universal screening, as well as to improve its efficacy by using specific cut-off points in different groups.

Material and methods

A total of 1338 urine samples were analysed by flow cytometry (Sysmex UF-1000i), as well as a urine culture in CPS agar. Cultures with one or two pathogens and more than 10,000 CFU/ml, and special cases with less counts but just one pathogen, were considered as positive.

Results

A cut-off of > 17.1 bacteria/μl or > 29.5 leucocytes/μl resulted with a sensitivity of 95.15% and a screening yield of 32.14%. Eleven false negative were obtained, but six of them showed low counts, and another was due to Candida glabrata. On the other hand, statistically significant variations were found as regards gender and origin of the patients. The cut-off of male samples was lower than female ones. However, it remained stable in the samples from Primary Care, and it decreased notably in those from the hospital. The negative predictive value always remained over 95%.

Conclusion

Automated flow cytometry can avoid the culture of 32% of samples, even after applying tight positive criteria. In the study hospital, it would have avoided the culture of 13,705 urine samples in the year 2016. These results could improve by combining cut-off points, gender, and origin of patients.

Introduction

As too many laboratory tests may not represent significant improvements, their efficient use should be considered. Bilirubin is a classical biochemical marker of hepatic alterations, and the icteric index is an indirect measure for the semi-quantitative determination of jaundice.

Objectives

To evaluate the use of the icteric index in the identification of patients with serum bilirubin concentrations with values higher or lower than 1.20 mg/dL, as well as to assess the determination of bilirubin, and to evaluate the savings that the application of this algorithm would represent.

Material and methods

A retrospective study was performed to determine the relationship between icteric index and total bilirubin. A regression analysis was also performed. The diagnostic efficiency of the index was studied using a Receiver Operating Characteristic curve to determine the cut-off value that would allow to distinguish bilirubin values higher and lower than 1.20 mg/dL. The sensitivity and specificity, positive predictive value and negative predictive value were also calculated.

Results and discussion

The statistical analysis showed a high correlation between both variables. The study of diagnostic efficacy showed that to use an icteric index equal to 2 as a cut-off point yields a high negative predictive value, sensitivity and specificity.

Conclusions

Icteric index values are well correlated with bilirubin, which allows filtering for hyperbilirubinaemia. Therefore, 89.72% of bilirubin requests would not be needed. With those samples with icteric index ≤ 1 subsequently being reported as < 1.20 mg/dL, thus representing a savings to the laboratory.

Collection and transport of semen samples can have an influence on the laboratory analysis results. The design and implementation of a protocol suitable for the pre-analytical phase is required in order to offer accurate results. This document is intended to provide a series of recommendations on the information that should be included in the instructions to the patients. Furthermore, it mentions pre-analytical confounders, such as the period of sexual abstinence, the location where the semen sample was obtain, as well as explanatory variables, included in a sample reception checklist.

Biological reference intervals do not provide sufficient information for the interpretation of a change between two consecutive measured values of a biological quantity because, for the vast majority of quantities, the intra-individual biological variability is smaller than the inter-individual biological variability. Taking into account this situation, the laboratory could provide, in conjunction with the reference intervals, additional information to objectively estimate the significance of a change in the values of a biological quantity. In this sense, the most adequate way to interpret the change must be made on the basis of the uncertainty concept, since it allows taking into account all the possible sources of variation to which the measured values are subjected. This document, based on national and international guidelines, describes a procedure for the interpretation of a change between two consecutive values of a biological quantity, based on the study of the various sources of uncertainty that affect it.

Phosphorus is the second most important mineral in the body. Its homeostasis is maintained through several mechanisms mediated mainly by the kidney, intestine, and bone. Interferences have been described in the measurement of phosphorus that could suggest a pseudo-hyperphosphataemia. The most frequent cause was the presence of a paraprotein in the serum of patients with multiple myeloma, Waldenström macroglobulinaemia, or monoclonal gammopathy of uncertain significance, was described as the most frequent cause of interference in phosphorus assay using liquid chemistry autoanalysers. When hyperphosphataemia is present, and no apparent cause can justify it, it is important to consider the possibility of a pseudo-hyperphosphataemia caused mainly by the presence of a paraprotein. The Vitros® 5600 multilayer system can be used as a fast and reliable method to avoid this interference.