Xavier Fuentes-Arderiu

Need for revisiting the concept of reference values.

Abstract The reference values concept has been adopted by health care professionals, including clinical chemists, laboratory scientists, and clinicians and simultaneously by all the official organizations in charge of the establishment of legislation. But the estimation of reference limits, and the evaluation of biological variability need to be improved at the level of the procedures, which are currently too long and too expensive and not feasible easily for all laboratories. The procedures for obtaining reference values, if we follow the original documents, are complex, and that is the main reason that clinical chemists or diagnostic kit manufacturers have not used them systematically. There is clearly a need that scientific societies and international organizations propose practical recommendations: 1) Recommendations to describe methods linked to systematic error. · How to transfer reference limits from one laboratory to another laboratory using different methods? · Should we determine reference limits for each method? · How can we differentiate bias due to the populations from these due to the method? Clear collaborations with manufacturers involved in kits and diagnostic systems are needed. 2) Practical recommendations linked to the reference population. · How to transfer reference limits from one laboratory to another laboratory using different methods? · Should we determine reference limits for each method? · How can we differentiate bias due to the populations from these due to the method? Clear collaborations with manufacturers involved in kits and diagnostic systems are needed. · How to select a homogenous population? (Careful recommendations on the choice between healthy individuals, blood donors and individuals hospitalised for other diseases should be given.) · How to estimate ethnic differences? · How to define the exclusion and inclusion criteria according to quantity? · How to deal with the question of reference limits for unstable periods, aging or old people particularly, when the difference between aging and disease is very difficult to define? 3) Practical recommendations on the statistical methods to be used. · How to transfer reference limits from one laboratory to another laboratory using different methods? · Should we determine reference limits for each method? · How can we differentiate bias due to the populations from these due to the method? Clear collaborations with manufacturers involved in kits and diagnostic systems are needed. · How to select a homogenous population? (Careful recommendations on the choice between healthy individuals, blood donors and individuals hospitalised for other diseases should be given.) · How to estimate ethnic differences? · How to define the exclusion and inclusion criteria according to quantity? · How to deal with the question of reference limits for unstable periods, aging or old people particularly, when the difference between aging and disease is very difficult to define? · How to make a good choice of the interquantile interval? Should we use and present only the centiles 2.5 or 97.5, or on the contrary should we give other centiles in addition, for example 5, 10, 75, 80, 85, 90? 4) Practical recommendations linked to the use of the concept of the reference values. · How to transfer reference limits from one laboratory to another laboratory using different methods? · Should we determine reference limits for each method? · How can we differentiate bias due to the populations from these due to the method? Clear collaborations with manufacturers involved in kits and diagnostic systems are needed. · How to select a homogenous population? (Careful recommendations on the choice between healthy individuals, blood donors and individuals hospitalised for other diseases should be given.) · How to estimate ethnic differences? · How to define the exclusion and inclusion criteria according to quantity? · How to deal with the question of reference limits for unstable periods, aging or old people particularly, when the difference between aging and disease is very difficult to define? · How to make a good choice of the interquantile interval? Should we use and present only the centiles 2.5 or 97.5, or on the contrary should we give other centiles in addition, for example 5, 10, 75, 80, 85, 90? · How to make this concept more concrete and to have official definitions which are better understandable and not only abstract? · How to demonstrate the value of using simultaneously reference limits and decision limits, and what does each of these limits bring to results interpretation? · How to improve the presentation of the results? How to give more information on biological variability in the laboratory data, taking into account the scientific validity of their determination? Should we use new information techniques and new communication systems for reaching these objectives? The responses to all these questions could only be provided if there is a concerted effort at the international level. Practical recommendations should be given, which would be very useful for a better understanding and use of reference values by laboratory scientists and clinicians.

Annual rhythmic variations of follitropin, lutropin, testosterone and sex-hormone-binding globulin in men

The annual rhythmic variations of the serum concentrations of follitropin, lutropin, sex-hormone-binding globulin and testosterone, the ratio between the serum concentrations of testosterone and sex-hormone-binding globulin, and the salivary concentration of testosterone were investigated in a group of 20 apparently healthy men. Venous blood and salivary specimens were collected at 1-month intervals during 12 months. The annual rhythms were studied by using a periodic function resulting from the sum of three cosine functions with periods of 365, 182.5 and 121.66 days. For the salivary concentration of testosterone and for the ratio between the serum concentrations of testosterone and sex-hormone-binding globulin, only the cosine function with a period of 365 days was significant, and for the serum concentration of lutropin, only the cosine function with a period of 121.66 days was significant. Serum concentrations of follitropin, sex-hormone-binding globulin and testosterone were significantly affected by 365 and 121.66 rhythmic components. The salivary concentration of testosterone and the serum concentration of follitropin are the quantities with the greatest annual rhythmic variation of those studied.

Guideline for the production of multicentre physiological reference values using the same measurement system. A proposal of the Catalan Association for Clinical Laboratory Sciences.

Abstract This article is intended as a guide for the production of biological reference values of healthy people (physiological reference values) by several clinical laboratories using the same measurement system. This guide is a proposal from the Catalan Association of Clinical Laboratory Sciences to be applied worldwide at a regional level. This guide makes it possible for all clinical laboratories in a region using the same measurement system to adopt the same physiological reference limits. The model presented here is based on the assumption that the production of physiological reference values is a professional task that should be shared by both clinical laboratories and the in vitro diagnostics industry.

An outline for a vocabulary of nominal properties and examinations - basic and general concepts and associated terms

Abstract Scientists of disciplines in clinical laboratory sciences have long recognized the need for a common language for efficient and safe request of investigations, reporting of results, and communication of experience and scientific achievements. Widening the scope, most scientific disciplines, not only clinical laboratory sciences, rely to some extent on various nominal examinations, in addition to measurements. The ‘International vocabulary of metrology – Basic and general concepts and associated terms’ (VIM) is designed for metrology, science of measurement. The aim of the proposed vocabulary is to suggest definitions and explanations of concepts and terms related to nominal properties, i.e., properties that can be compared for identity with other properties of the same kind-of-property, but that have no magnitude. Clin Chem Lab Med 2010;48:1553–66.

Multicentric reference values for some quantities measured with the Elecsys 2010® analyser

Several clinical laboratories in different regions of Spain have shared the search for reference individuals and the production of reference values for quantities concerning thyrotropin, non-protein bound thyroxine, triiodothyronine, cobalamines and folates, using an Elecsys 2010 analyser. All the logistic work has been done in co-operation with the supplier of the analyser (Roche Diagnostics España, S.L., Barcelona). The reference limits produced in the virtual laboratory are in fact derived from the blend of reference values obtained by each laboratory. The multicentric reference limits were estimated according to the recommendations of the International Federation of Clinical Chemistry. The work done represents a model of co-operation between the in vitro diagnostic industry and clinical laboratories for the production of reference values.

Measurement uncertainty in manual differential leukocyte counting.

Abstract Background: One of the most frequently requested examinations in the clinical laboratory is the differential leukocyte count. Despite many technological improvements, thousands of differential leukocyte counts are made by microscopic examination of a blood smear, counting 100 leukocytes and expressing the fraction of the specific leukocyte types as percentages (rounded to integer values) of the total leukocyte count. Although in the clinical laboratory it is not usual practice to report measurement uncertainties, currently the ISO 15189 standard considers measurement uncertainty as a very helpful element for a comprehensive interpretation of any measurement result. Methods: The estimation of the measurement uncertainty of each differential leukocyte count result was carried out according to international guidelines. The sources of standard uncertainty taken into account were: pre-metrological variation, random distribution, between-examiner reproducibility, and rounding to an integer. Results: In this example, a sample of blood with a concentration number of leukocytes of 3,5×109/L 1) is taken into consideration. For each differential leukocyte count result, the standard uncertainties corresponding to each source of measurement uncertainty, as well as the combined and the expanded uncertainties, were estimated with information from the literature. Conclusions: The procedure presented here to estimate the measurement uncertainty of differential leukocyte count results is appropriate to fulfill the requirements of the ISO 15189 standard related to measurement uncertainty. Knowledge of this uncertainty is helpful in interpreting sequential results obtained in the same patient. Clin Chem Lab Med 2009;47:112–5. 1) According to ISO, IUPAC and IFCC recommendations, the comma is used as the decimal sign.

Daily Rhythmic and Non-Rhythmic Variations of Follitropin, Lutropin, Testosterone, and Sex-Hormone-Binding Globulin in Men

The circadian rhythmic variations of the serum concentrations of follitropin, lutropin, sex-hormone-binding globulin and testosterone, the ratio between the serum concentrations of testosterone and sex-hormone-binding globulin, and the salivary concentration of testosterone were investigated in a group of 13 apparently healthy men. Venous blood and salivary specimens were collected at 4-h intervals over a 24-h period. The circadian rhythms were studied by using a periodic function resulting from the sum of two cosine functions with periods of 24 and 12 h. The serum concentrations of follitropin and lutropin showed no significant rhythmic variations. For the salivary concentration of testosterone and for the ratio between the serum concentrations of testosterone and sex-hormone-binding globulin, only the cosine function with a period of 24 h was significant. Serum concentrations of sex-hormone binding globulin and testosterone were significantly affected by 24- and 12-h rhythmic components. Of the quantities studied, the salivary concentration of testosterone showed the greatest daily rhythmic variation (28.8% of the mean estimated over rhythm).

Multicentre physiological reference values for the concentration of creatininium in plasma and diagnostic specificity of glomerular filtration rate estimated with the MDRD equation

Abstract Background: The National Kidney Disease Education Program recommends that clinical laboratories, when asked for an estimation of glomerular filtration rate in a patient by means of the “four-variable” Modification of Diet in Renal Disease (MDRD) Study equation, also provide the measurement result for creatininium concentration in plasma and the appropriate reference interval. On the other hand, clinical laboratories seeking accreditation for compliance with ISO 15189:2003 need to demonstrate that the physiological reference intervals communicated to all users of laboratory services are appropriate for the patient population served, and for their measurement systems. Methods: Ten clinical laboratories in different regions of Spain collaborated in identifying reference individuals and producing reference values for the concentration of creatininium in plasma using RD/Hitachi Modular Analytics analysers, and for the volume rate of glomerular filtrate in kidneys (glomerular filtration rate), estimated with the “four-variable” MDRD Study equation. All the logistic work was carried out in co-operation with the supplier of the reagents and analysers (Roche Diagnostics España, S.L., Sant Cugat del Vallès, Catalonia, Spain). Using all the reference values obtained by each laboratory, multicentre reference limits were estimated non-parametrically. Results and conclusions: Reference intervals estimated in this study for concentrations of plasma creatininium are 52–85 μmol/L for women and 64–106 μmol/L for men. The diagnostic specificity of the estimated glomerular filtration rate is 99,2% when applied to healthy persons to screen for chronic kidney disease. Clin Chem Lab Med 2007;45:531–4.

What is a biomarker? It’s time for a renewed definition

following definition of biomarker (or simply marker) might be provisionally used: “human or animal biological property whose in vitro measurement or identification is useful for the prevention, diagnosis, prognosis, treatment, and follow-up of human or animal diseases, and for their understanding”. As a final clarification, it should be kept in mind that in the field of clinical pharmacology (clinical trials) the concept of “biomarker” has a wider meaning than in clinical laboratory sciences: some biomarkers are in vitro measured or identified and others in vivo. In the field of clinical laboratory sciences, as reflected in the proposed definition, the concept of “biomarker” is always related to in vitro measurements or identifications.

Disadvantages of using biological variation data for reference change values.

Recently, a mini review and an Editorial on reference change values (RCV) were published in this journal (1, 2) . The leitmotif of the mini review is the use of the within-subject biological variation for estimating the RCV of many quantities measured in the clinical laboratory. The Editorial strongly endorsed this approach. Notwithstanding, the review article has one paragraph devoted to the “ Potential disadvantages of RCV ” . We agree with these, but we think that the within-subject biological variation approach for RCV has several weaknesses which highlight other disadvantages that should be added to this point. In our opinion these drawbacks that are not mentioned in the review are so relevant that they may invalidate the use of the RCV based in the within-subject biological variation. The main real disadvantages are the following: