The reference change value: a proposal to interpret laboratory reports in serial testing based on biological variation.

BACKGROUND: A proposal to calculate and use the reference change value (RCV) as an objective guide for interpreting the numerical results obtained in clinical laboratory serial testing is introduced in this study. METHODS: A database showing the results of a compilation of 191 publications on biological variation and including information on a number of analytes provided the standardized criterion based on biology for calculating the RCVs. RESULTS: For each of the 261 analytes included in the study, the RCV was determined using Harris's formula, replacing analytical imprecision with the desirable specification of analytical quality based on half the within-subject biological variation at 95% probability levels. The result is a guide for a common criterion to identify clinically significant changes in serial results. CONCLUSIONS: The RCV concept is an approach that can be offered by laboratories to assess changes in serial results. The RCV data in this study are presented as a point of departure for a widely applicable objective guide to interpret changes in serial results.

Are equally spaced specimen collections necessary to assess biological variation? Evidence from renal transplant recipients.

The established method for determining the components of biological variation (BV) requires equispaced time intervals between samplings. In a previous study, we determined BV in renal post transplantation patients, taking advantage of the samples obtained within their clinical treatment protocol (not necessarily equispaced). To confirm the validity of this practice, we sought to determine if the use of varying sampling intervals has an effect on the results obtained in such biological variation studies. The study included two phases: comparison of the results found with identical and non-identical sampling intervals and correlation between the within-subject BV and the length of the sampling interval. There were no differences in within-subject BV between the groups or correlations with sampling intervals for any of the constituents studied. We conclude that samples acquired within established clinical protocols for kidney transplant recipients can be used for estimating BV.

Commutability and traceability: their repercussions on analytical bias and inaccuracy.

The commutability of calibrators and accuracy control materials affects the traceable link between patient sample results and standards. We sought to identify the repercussions of commutability on various aspects of laboratory practice (calibration, control of bias and accuracy assessment) and to discover the solutions that can reduce the problems produced by non-commutability with presently available resources. Ten serum constituents, ten comparison procedures and 37 analytical procedures were studied. The information concerning accuracy and bias provided from materials found to be commutable in previous works was challenged with native serum results for each routine and reference method compared, using Passing-Bablok regression and decision limits derived from biological variation. We found that: (1) Use of commutable control materials did not assure reliable information on the bias (systematic component of analytical error) of analytical procedures, and (2) Results from native serum and commutable controls were very highly concordant, indicating that these materials provide a good indication of the inaccuracy (total analytical error) of results. We suggest that the performance of individual laboratories would be better evaluated by occasional use of native sera with values assigned by reference methods in EQAS schemes. Moreover, our findings support the idea that manufacturers should assign values to calibrators using reference methods and native sera to reduce matrix effects and promote traceability.

Current databases on biological variation: pros, cons and progress.

A database with reliable information to derive definitive analytical quality specifications for a large number of clinical laboratory tests was prepared in this work. This was achieved by comparing and correlating descriptive data and relevant observations with the biological variation information, an approach that had not been used in the previous efforts of this type. The material compiled in the database was obtained from published articles referenced in BIOS, CURRENT CONTENTS, EMBASE and MEDLINE using "biological variation & laboratory medicine" as key words, as well as books and doctoral theses provided by their authors. The database covers 316 quantities and reviews 191 articles, fewer than 10 of which had to be rejected. The within- and between-subject coefficients of variation and the subsequent desirable quality specifications for precision, bias and total error for all the quantities accepted are presented. Sex-related stratification of results was justified for only four quantities and, in these cases, quality specifications were derived from the group with lower within-subject variation. For certain quantities, biological variation in pathological states was higher than in the healthy state. In these cases, quality specifications were derived only from the healthy population (most stringent). Several quantities (particularly hormones) have been treated in very few articles and the results found are highly discrepant. Therefore, professionals in laboratory medicine should be strongly encouraged to study the quantities for which results are discrepant, the 90 quantities described in only one paper and the numerous quantities that have not been the subject of study.

Commutability between stabilized materials and fresh human serum to improve laboratory performance.

With the recent advances in laboratory technology, many quality-related problems have been improved. However, the issue of commutability, a factor that greatly affects daily decisions concerning patient status, still remains to be solved. This paper determines the commutability between 27 stabilized materials (controls and calibrators) and clinical specimens for five serum quantities, using carrier-bound reagent chemistry and conventional wet methods. Our aim was to pinpoint the specific problems related to non-commutable calibrators and controls in our setting, and minimize their effect in daily practice. We found major difficulties in selecting appropriate accuracy controls in carrier-bound reagent techniques, and in finding materials commutable for several analytes simultaneously. Several suggestions for reducing problems related to non-commutability, such as procedures for assigning values to multicalibrators, are proposed. We explain the apparent incongruencies observed in daily quality surveillance, when data from different control materials (internal quality control and external quality assessment) are evaluated. The conclusions emphasize the need for a combined effort (manufacturers, organizers of external quality assessment schemes and individual laboratories) to find the cause of, and eliminate, the negative repercussions on laboratory performance produced by non-commutability.

Procedure for studying commutability validated by biological variation.

In the field of laboratory medicine, the two quantitative approaches designed to identify the stabilized materials that produce results that are commutable with results from patients' samples were found to differ. In commutability evaluations, the responses of each material and each method studied are specific, thus, it is vital to standardise the procedure used for determining this characteristic. We incorporated statistical components from the two described methods that seemed to be consistent, and added a new element based on biological variation, to validate the criterion of acceptability that determines whether or not a material is commutable. The three methods for studying commutability (using the confidence interval [alpha = 0.05], the +/- 2s(yx) formula, and the limit based on biological variation as acceptability criteria) were applied to creatinine results from 31 stabilised materials and serum samples analysed with seven instruments, when compared against a reference method for creatinine analysis. Over the wide range of concentrations studied, the confidence interval limit and the biological variation limit coincided in the identification of commutable materials, whereas the +/- 2s(yx) was excessively permissive at normal and low concentration levels. We therefore recommend the use of Passing-Bablok regression with its confidence interval (alpha = 0.05) in studies concerning commutability. Using this method, commutability is simple to calculate with available software and, as validated by biological variation, results are reliable.

New indices from the H*2 analyser improve differentiation between heterozygous beta or delta beta thalassaemia and iron-deficiency anaemia.

The two main causes of microcytic and hypochromic anaemia are iron deficiency (IDA) and thalassaemia (THAL) traits. In the Mediterranean area there is a high prevalence of beta and delta-beta THAL minor. The differentiation between these causes of microcytosis can be significantly improved with two new indices, percentage of microcytes (%Mi) and percentage of hypochromic red blood cells (%Hy), and the direct determination of MCHC, provided by the technological advances of the H*2 analyser. Our discriminant analysis, based on the minimization of Wilk's lambda (lambda) criterion, was used to select the best predictive variables to differentiate between IDA and THAL and has resulted in the highest diagnostic efficiency published to date. The discriminant function obtained is a simple linear combination of the following variables: D = 1.145 RBC-0.174 MCV + 0.091 MCHC + 0.787 square root of (%Hy/%Mi)-22.119. The overall correct classification was 97.6% on the training sample (79 THAL and 90 IDA) and 96.7% on a validation sample of microcytic patients (72 THAL and 80 IDA). The sensitivity and diagnostic specificity were 97.5% and 97.8%, respectively, for the training sample, and 95.8% and 97.5% for the control group.

[Transferability of results in hematologic determinations]. / Transferibilidad de los resultados en determinaciones hematológicas.

PURPOSE: To evaluate inaccuracy of the results attained in several Servei Catalá de la Salut laboratories in order to assess if quality purposes are accomplished and results are transferable between them. MATERIAL AND METHODS: Two types of haematological analysers are used: those based upon volumetric measurements and those using light dispersion for particle counting. Inaccuracy was ascertained in accordance to the inter-laboratory quality control programme. The inter-series study was performed with commercial control material in each laboratory with their own data, the monthly coefficient of variation being found, and the mean of the CV of 12 months was then calculated. Intra-series inaccuracy with commercial control material was assessed in each laboratory three times a day for 10 days, and the inaccuracy with fresh patient blood was examined daily in triplicate. The analytical inaccuracy attained in patient samples was also compared with that attained with stabilized control materials. RESULTS: The inaccuracy quality limits were exceeded in the haematological constituents under study. Quality objectives were accomplished in the inter-series inaccuracy study for red cell count, white cell count, MCV, granulocytes and lymphocytes. Repeat fresh patient-blood assays can be used to assess intra-series inaccuracy for red and white cell counts, but not for platelet count. CONCLUSIONS: Inaccuracy of the blood constituents studied is not transferable. Inaccuracy for the commonest haematological values is transferable between laboratories. Intra-series inaccuracy for red and white cell counts can be assessed by repeated use of fresh patient-blood when control material is not available. Patient samples are not advisable as a control of the white cell differential count for intra-series inaccuracy studies in those systems using volumetric principles.

Biological variation in urine samples used for analyte measurements.

To determine the influence of biological variation on the reliability of data from different types of urine specimens, we measured nine analytes in first-morning, randomly collected, and 24-h samples of urine from 53 healthy individuals (14 men and 39 women). The urines were collected once a week for 10 weeks. The data obtained were used as a basis for specimen collection and to gain insight into the influence of urine quantities in the diagnosis, screening, and monitoring of patients. We found that 24-h urine expressed in output rather than concentration units is the most reliable specimen for diagnosis and monitoring for most of the analytes studied. On the basis of the ratio between estimated within- and between-subject variation, the tests with greatest medical usefulness for diagnosis and screening of specific pathologies are those measuring protein and sodium. Moreover, the results indicate that urine creatinine may be a poor test for diagnosis, monitoring, and screening.

Usefulness of reference limits and evaluation of significant differences. An example of the biological variation of serum rheumatoid factors.

To establish analytical quality standards based on biological variations and to evaluate the usefulness of reference values for rheumatoid factors (RF), analytical and biological variations in samples from 34 volunteers between 23 and 46 years old were estimated at monthly intervals for six months. The samples were processed in duplicate on a Hitachi 717 automatic analyzer using the manufacturer's reagents. The within- and between-subject coefficients of variation associated with RF were 8.5% and 24.5% respectively, and the individuality index was 0.45, indicating the high individuality of this parameter. The analytical standards of quality estimated as coefficients of variation (%) were: imprecision, 4.2% and inaccuracy, 6.5%. The heterogeneity index of the within-subject variances was 0.17, thus not rejecting the homogeneity hypothesis. The RF may be considered useful for monitoring purposes because of their high individuality and relatively small critical difference (25% for alpha = 0.10). However, when RF levels are normal it is difficult to interpret them because of their high between-subject variability.

Iron-deficiency anemia and thalassemia trait differentiated by simple hematological tests and serum iron concentrations.

The diagnostic value of common hematology tests in differentiating between thalassemia trait and iron-deficiency anemia (IDA) was assessed. Serum iron concentration was included in a second stage of the diagnostic model and its predictive contribution was determined. After applying discriminant analysis to the data, minimization of Wilks's lambda (lambda) criterion was used to select the best predictive variables. A training sample of 754 subjects previously classified as either IDA (428) or thalassemia trait (326) was used to determine the classification rule. When serum iron concentrations were included, the model showed a higher predictive capacity than that constructed from hematological variables only (D = 2.342 RBC - 0.079 Hb + 3.627 log[Fe] - 6.459, where D = discriminant score). The sensitivity, specificity, and diagnostic efficiency associated with this model, as assessed on a control sample of 256 patients (137 thalassemia and 119 IDA), were 94.2%, 91.6%, and 93.0%, respectively. This model, when compared with those of other authors, has the highest diagnostic efficiency.

Approaches for providing target values to improve usefulness of external quality assessment scheme. The Spanish experience.

The aim of this communication is to highlight the specific aspects of external quality assessment schemes that need to be discussed in a European context: target values, transferability of results and accredit of laboratories. The Spanish situation is presented here. The most reliable way to provide target values is to analyse the control samples by reference methods. However, it is not possible for the majority of national schemes and other approaches are presently used: the verification of consensus means is a practicable solution adopted in Spain. An initial network involving selected routine laboratories has been developed, to attain transferability of results. The traceability of routine calibrators from certified reference materials should be demonstrated. To accredit laboratories for licensing is a complex activity that should consider many aspects, results from the national quality assessment scheme bring one. A scoring system is being used in Spain for guidance, and the complete guidelines are under preparation.

[Importance of salivary levels of theophylline in monitoring pediatric asthmatic patients]. / Interés de los niveles salivares de teofilina en la monitorización de pacientes asmáticos pediátricos.

In order to maintain theophylline serum levels between 10 and 20 mcg/ml., obtaining an average dose of 26.36 +/- 6.42 mg/kg/d (range 11.42 mg/kg/d-48 mg/kg/d), authors have determined average dose of oral theophylline intake needed in a group of 212 infants, 1 to 15 years of age. Statistical analysis of 717 salivary and blood theophylline values simultaneously obtained (both at therapeutic and subtherapeutic levels), was carried out reading a lineal correlation coefficient of 0.93. Correlation that has been sufficiently worked out in many other papers. Once necessary dose for obtaining salivary and blood theophylline therapeutic levels is determined, salivary theophylline concentration may be used as a nonaggressive method control of outpatients, assuring their intake continuity between medical controls and as a good seric level index in a given patient.