BACKGROUND:The improvement of the consistency of gamma-glutamyltransferase (GGT) activity results among different assays after calibration with a common material was estimated. We evaluated if this harmonization could lead to reference limits common to different routine methods.METHODS:Seven laboratories measured GGT activity using their own routine analytical system both according to the manufacturer's recommendation and after calibration with a multi-enzyme calibrator [value assigned by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference procedure]. All samples were re-measured using the IFCC reference procedure. Two groups of subjects were selected in each laboratory: a group of healthy men aged 18-25 years without long-term medication and with alcohol consumption less than 44 g/day and a group of subjects with elevated GGT activity.RESULTS:The day-to-day coefficients of variation were less than 2.9% in each laboratory. The means obtained in the group of healthy subjects without common calibration (range of the means 16-23 U/L) were significantly different from those obtained by the IFCC procedure in five laboratories. After calibration, the means remained significantly different from the IFCC procedure results in only one laboratory. For three calibrated methods, the slope values of linear regression vs. the IFCC procedure were not different from the value 1. The results obtained with these three methods for healthy subjects (n=117) were gathered and reference limits were calculated. These were 11-49 U/L (2.5th-97.5th percentiles). The calibration also improved the consistency of elevated results when compared to the IFCC procedure.CONCLUSIONS:The common calibration improved the level of consistency between different routine methods. It permitted to define common reference limits which are quite similar to those proposed by the IFCC. This approach should lead to a real benefit in terms of prevention, screening, diagnosis, therapeutic monitoring and for epidemiological studies.

L'IFCC (International federation of clinical chemistry laboratory medicine) a recemment publie des procedures de reference primaires pour la determination d'activites enzymatiques a 37 iC. Cette presentation vise a donner des informations concernant les modifications intervenues, ainsi que l'approche suivie par la Federation pour l'amelioration de la standardisation en enzymologie clinique. Les modifications concernent a la fois les biologistes des LABM, les industriels et les organisateurs d'enquetes d'evaluation de la qualite. L'ensemble des informations peut etre obtenu dans les publications citees a la fin de cet article ou aupres du groupe de travail Assurance de qualite en enzymologie clinique par l'intermediaire du site SFBC.

BACKGROUND:Apolipoprotein (apo) E is a component of two major classes of plasma lipoproteins, apo B- (apo E-LpB) and non-apo B-containing (apo E-Lp-non-B) lipoproteins. The factors that affect total apo E in particles [lipoprotein E (LpE), apo E-Lp-non-B, and apo E-LpB], are incompletely characterized.METHODS:We studied the determinants of these lipoparticles in a sample population of presumably healthy individuals: 1784 children (age range, 8-18 years) and 1739 adults (age range, 19-50 years). Serum concentrations of LpE and apo E-Lp-non-B were measured by electroimmunoassays, and the concentration of apo E-LpB was calculated by a difference method.RESULTS:Serum LpE and apo E-Lp-non-B were higher in females than in males. Their concentrations decreased with age until 20-25 years and then increased in men but not in women. apo E-LpB concentrations increased up to 20-25 years and were similar in both sexes. Thereafter, adult men had higher values than women. Individuals carrying the epsilon2 allele had higher mean apo E-Lp-non-B concentrations and lower apo E-LpB concentrations than did individuals carrying the epsilon3 allele. Individuals with the epsilon4 allele showed an inverse profile compared with those with the epsilon2 allele. Age, gender, the common apo E polymorphism, puberty, serum lipid concentrations, and alcohol consumption were significantly associated with total LpE, apo E-Lp-non-B, and apo E-LpB concentrations. Reference limits were established according to age, gender, and the common apo E polymorphism.CONCLUSIONS:Because measurements of LpE, apo E-Lp-non-B, and apo E-LpB concentrations may improve cardiovascular risk assessment, the proposed reference limits will aid interpretation of the results in clinical or therapeutic trials.

Les resultats des mesures d'activite catalytique d'une enzyme sont hautement dependants des methodes choisies et des conditions locales de realisation. Ainsi, on observe peu d'amelioration de la coherence interlaboratoire des resultats. C'est pourquoi, la SFBC et l'IFCC ont propose de resoudre cette question par l'approche des « calibrateurs valides d'enzymes ». Des procedures standardisees, adaptees a 37 °C, ont ete elaborees par l'IFCC et seront prochainement publiees pour la mesure des activites enzymatiques les plus couramment utilisees en biologie clinique. Elles ont permis de certifier des materiaux de reference d'enzyme qui peuvent servir de calibrateurs pour un groupe de methodes presentant la meme specificite analytique. Les calibrateurs doivent par ailleurs etre commutables, propriete qui doit etre testee experimentalement. Il est possible de produire des materiaux stables et commutables pour le calibrage d'un groupe de methodes. L'interet de cette approche a ete demontre pour plusieurs enzymes. Les resultats de deux etudes presentees ici indiquent que la comparaison a la limite superieure de l'intervalle de reference ne permet pas d'ameliorer la coherence interlaboratoire des resultats de plusieurs activites enzymatiques, au contraire de l'emploi d'un calibrateur commun qui permet d'obtenir un CV interlaboratoire de l'ordre de 4 % pour l'ALT et la gammaGT.

This paper is the sixth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37degreesC and the certification of reference preparations. Other parts deal with:Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37degreesCA document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30degreesC IFCC reference method (1). Differences are tabulated and commented on in Appendix 1.

Results of catalytic activities of enzymes are highly dependent on the measurement procedures and on local conditions. Thus, only poorly marked improvement of interlaboratory comparability of results have been observed in clinical enzymology. To solve this problem, SFBC and IFCC have proposed to use "validated enzyme calibrators". Standardised operating procedures adapted to 37 C have been developed by IFCC for the most commonly used enzymes in clinical chemistry, and will be soon published. Reference materials which have been certified with these SOPs can be used as calibrators for a set of measurement methods which exhibit the same analytical specificity. Calibrators must be commutable, a property that must be checked experimentally. It is possible to produce stable and commutable materials for the calibration of a set of methods. Interest of this approach has been demonstrated for several enzymes. Results of two studies presented here show that the comparison of results to the upper limit of reference ranges does not improve the interlaboratory comparability of results in contrast to the calibration of different methods by a common calibrator which allowed to reach an interlaboratory CV close to 4% for ALT and gammaGT.

This paper is the fourth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 degrees C and the certification of reference preparations. Other parts deal with: Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 5. Reference Procedure for the Measurement of Catalytic Concentration of Aspartate Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of Gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of Gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37 degrees C. A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30 degrees C IFCC reference method. Differences are tabulated and commented on in Appendix 2.

Article Serum Total Antioxidant Status Is Higher in Postmenopausal Women and after Estrogen Replacement Therapy was published on August 26, 2002 in the journal Clinical Chemistry and Laboratory Medicine (CCLM) (volume 40, issue 8).

This paper is the eighth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 378C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase; Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase; Part 6. Reference procedure for the measurement of catalytic concentration of g-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of g-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 378C. The procedure described here is deduced from the previously described 308C IFCC reference method. Differences are tabulated and commented on. Clin Chem Lab Med 2006;44:1146–55. Schumann et al.: IFCC primary reference procedures 1147 Article in press uncorrected proof Table 2 Conditions for the measurement of a-amylase. Temperature 37.08C"0.18C Wave length 405 nm "1 nm Band width F2 nm Light path 10.00 mm "0.01 mm Incubation time 60 s Delay time 180 s Measurement interval 180 s Readings (measurement points) G6 Table 1 Concentrations in the final complete reaction mixture for the measurement of a-amylase. N-2-Hydroxyethylpiperazine-N9-ethanesulfonic acid 50 mmolOl pH (378C) 7.00"0.03 4,6-Ethylidene(G1)-4-nitrophenyl(G7)-a-(1TM4)-D-maltoheptaoside 5 mmolOl Sodium chloride 70 mmolOl Calcium chloride 1 mmolOl a-Glucosidase (378C) 135 mkatOl (8100 UOl)* Volume fraction of sample 0.0323 (1:31) *Uninhibited catalytic concentration. Note: The indicated catalytic concentration of a-glucosidase shall be measured in the final complete reaction mixture if 9 gOl (154 mmolOl) sodium chloride solution is used as the sample (no inhibition by the sample matrix). Note: Besides the substances listed in Table 1, the final complete reaction mixture contains 0.1 gOl albumin, which is originally a component of Solution 3. The presence of albumin in the Reaction Solution and consequently in the final complete reaction mixture stabilizes the a-glucosidase.

This paper is the fifth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37degreesC and the certification of reference preparations. Other parts deal with:Part 1. The Concept of Reference Procedures for the Measurement of Catalytic Activity Concentrations of Enzymes; Part 2. Reference Procedure for the Measurement of Catalytic Concentration of Creatine Kinase; Part 3. Reference Procedure for the Measurement of Catalytic Concentration of Lactate Dehydrogenase; Part 4. Reference Procedure for the Measurement of Catalytic Concentration of Alanine Aminotransferase; Part 6. Reference Procedure for the Measurement of Catalytic Concentration of gamma-Glutamyltransferase; Part 7. Certification of Four Reference Materials for the Determination of Enzymatic Activity of gamma-Glutamyltransferase, Lactate Dehydrogenase, Alanine Aminotransferase and Creatine Kinase at 37degreesC.A document describing the determination of preliminary upper reference limits is also in preparation. The procedure described here is deduced from the previously described 30degreesC IFCC reference method (1). Differences are tabulated and commented on in Appendix 3.

Oral contraceptive (OC) use and common apo E polymorphism are well known to modify serum lipid and lipoprotein concentrations. The combined effect of OC use and apo E genotype on the concentration of apo E or apo C-III in apo B- (apo E-LpB or apo C-III-LpB) or in non-apo B-containing lipoparticles (apo E-Lp-non-B or apo C-III-Lp-non-B) are unknown. Our study comprised 613 women, aged 30-45 years, genotyped for common apo E polymorphism and who differed in their combined low-dose OC consumption. The concentrations of apo C-III, apo C-III-LpB and apo C-III-Lp-non-B were significantly higher in OC users than in non-users by 13, 23 and 8% respectively, without significant interaction with the apo E genotype. The concentrations of apo E and apo E-Lp-non-B were significantly lower (differences being -14% and -31% respectively) in OC users than in controls whereas the apo E-LpB concentration was significantly higher (+19%), resulting in a redistribution of apo E from Lp-non-B towards LpB. Total apo E and apo E-Lp-non-B concentrations were higher in subjects carrying the epsilon2 allele and lower in those with the epsilon4 allele when compared to epsilon3/epsilon3 subjects (P < 0.001). The opposite held for the apo E- LpB concentration (P < 0.05). The main finding is the significant interaction between apo E genotype and OC use (P < 0.01) on apo E-Lp-non-B concentration, the epsilon4 carriers showing the smallest differences between OC users and non-users in comparison with the epsilon2 or epsilon3/epsilon3 carriers. These results suggest that the common apo E polymorphism can modulate the OC use effect.

The large metrological variation (CV, about 25%) observed between laboratories, at the national French level, for the measurement of enzymatic activities results in a loss of efficiency in using laboratory results. Current data show that the standardisation of methods is insufficient to solve this problem and needs to be completed by an harmonisation of the practices including the use of a common reference (calibrator). The present work, carried out by the joint working group between laboratories of the Centres for Periodic Health Examination and the French Society of Clinical Biology (SFBC), deals mainly with the feasibility and evaluation of the improvement of the consistency of the results. Twenty laboratories participated in this study. Five independent surveys were conducted during an height month period. Two enzymes were selected because of their clinical importance and their interest in prevention, screening, diagnosis or epidemiology: ALT (alanine aminotransferase) and GGT (gamma-glutamyltransferase). In each survey three kinds of samples i.e. control sera, candidate calibrators and human serum pools, each of them at two levels of activity (one physiological and the other pathological) were measured in duplicate. The low intra-laboratory imprecision and the high degree of the standardisation of used methods, due to an important effort previously done in this field, permitted to consider a common calibration. The stability and mainly the commutability, i.e. the ability for the candidate calibrator to show a behaviour similar to that of human samples towards the used methods, allowed to reduce the inter-laboratory variation by a half to two third-fold, reaching a coefficient of variation < 5% similar to those observed for cholesterolemia or glycemia. This level of consistency should permit to use common reference limits and common decision limits, after validation of this approach in real practice. The consequences of the harmonisation of practices, extended to the all laboratories, exceed largely the scope of this study. The reduction of the uncertainty and a better approach of the accuracy for the measurement of enzymatic activities should led to a real benefit for the patients in terms of prevention, screening, diagnosis or therapeutic monitoring and consequently for the public health.

Le concept theorique de valeurs de reference est apparu dans les annees 1970 sous l'impulsion d'un groupe scandinave et notamment de R. Grasbeck [1, 2]. Parallelement a la proposition du concept, plusieurs groupes, tant scandinaves que nord-americains ont, a la meme epoque, initie une serie de travaux sur la variabilite affectant un examen de laboratoire [3-7]. Ces travaux fondateurs ont largement contribue a l'emergence d'une nouvelle approche de l'interpretation d'un examen de laboratoire : la notion de « constante biologique », prise dans son acception premiere avait definitivement vecu. En revanche, ces travaux n'ont pas connu l'audience qu'ils meritaient aupres de la communaute internationale des biologistes. Les efforts de deux groupes, un groupe francophone sous l'egide de la SFBC, puis ulterieurement a l'echelon international sous le patronage de l'IFCC-LM, ont formalise de facon approfondie le concept de valeurs de reference [8-28]. Le groupe francais a d'ailleurs associe a ses travaux des representants des societes de biologie clinique des pays francophones (Espagne, Belgique, Suisse et Canada). Les documents elabores de 1973 a 1983 ont precise le concept de valeurs de reference ainsi que les methodes de production, l'interet et l'utilisation des valeurs de reference. Des lors, les « valeurs de reference » ont ete largement popularisees aupres des instances supranationales, des pouvoirs publics, des administrations, des services de sante et bien evidemment des professionnels de sante eux-memes. Par exemple, les organismes internationaux les mentionnent dans les referentiels professionnels, reglementaires ou normatifs (par exemple : referentiel qualite EC4, norme ISO 15189), dans l'Union europeenne, la Directive 98/79/CE du 27 octobre 1998, fait obligation aux fabricants de communiquer des limites de references, avec une description de la population de reference consideree, sur les notices incluses dans les coffrets reactifs. Les biologistes sont tenus de les mentionner dans les comptes rendus d'analyse en application des recommandations internationales et nationales, notamment du guide de bonne execution des analyses (GBEA) en vigueur en France. Ce formidable succes du concept des valeurs de reference, maintenant universellement reconnu et applique, masque une realite moins rejouissante. En effet, au cours des annees ecoulees, la mise en œuvre des textes fondateurs ne l'a pas ete avec toute la rigueur qui impregnait l'esprit d'origine : bien souvent les professionnels confondent des notions aussi differentes que « valeurs de reference » ou « limites de reference », sans parler des « limites de decision ». Les methodes proposees dans la litterature pour les determiner se sont multipliees a tel point que bien des biologistes ne savent plus tres bien ce qui doit etre fait. Cela est du en grande partie au fait que ces recommandations sont trop theoriques et que leurs utilisateurs sous-estiment le travail necessaire a leur mise en œuvre. Il parait opportun de revoir d'un point de vue pratique les textes fondateurs et de developper l'usage des valeurs de reference grâce aux nouvelles technologies de l'information et de la communication. L'objet de cet article est donc d'attirer l'attention des biologistes sur la necessite d'agir vite, en vue de preciser le concept et de proposer une demarche pratique.

Background: We describe the preparation of a lyophilised reference material containing purified human adenosine deaminase I and the certification of its catalytic concentration. Methods: The enzyme was purified from human erythrocytes. Results: The enzyme was > 99% pure on polyacrylamide gel electrophoresis. Only trace amounts (< 0.4%) of alanine aminotransferase, aspartate aminotransferase and L-lactate dehydrogenase were detected in the purified fraction. The purified adenosine deaminase had a molar mass of 41 600 g/mol and an isoelectric pH at 4.7, 4.85 and 5.0. The material was prepared by diluting the purified adenosine deaminase in a matrix containing 50 mmol/l Tris-HCl buffer pH 7.4 and 30 g/l human serum albumin; dispensing in vials and freeze-drying. The batch was homogeneous and the predicted loss of adenosine deaminase activity per year on the basis of accelerated degradation studies was 0.006% at -20C and 0.04% at 4 degreesC. The certified value for adenosine deaminase catalytic concentration in the reconstituted reference material is (2.55 +/- 0.09) mu kat/l when measured by the method that uses adenosine as substrate and glutamate dehydrogenase as auxiliary enzyme at 37 degreesC. Conclusions: The material can be used to verify the comparability of results from different laboratories, for intra-laboratory quality control, or for calibration of the adenosine deaminase catalytic concentration measurements. (C) 2001 Elsevier Science B.V. All rights reserved.

In order to assess the short- and long-term stability of apolipoprotein (apo) E concentration in serum, we compared the apo E concentrations measured in fresh human serum samples with those determined after storage at +4 degrees C, -20 degrees C or -80 degrees C. The serum apo E concentration was measured by immunoturbidimetry using an anti-human apo E polyclonal antibody from goats. One week storage at +4 degrees C did not significantly affect the serum apo E concentration. At -20 degrees C or -80 degrees C no significant change in apo E concentration occurred during up to three months of storage. Moreover, the concentration of apo E was not modified after long-term storage of serum samples kept at -196 degrees C in liquid nitrogen for up to four years. In addition, 15 freeze-thaw cycles, over a 3-week period, did not affect the apo E concentration in serum. A similar freeze-thaw procedure applied to purified human recombinant apo E showed that apo E2 isoform was the most stable in comparison with the apo E3 and apo E4 isoforms.

Apolipoprotein (apo) E is an important circulating and tissue protein involved in cholesterol homeostasis and many other functions. The common polymorphism in the coding region of the gene, four polymorphisms in the promoter region, other additional single nucleotide polymorphisms, as well as several apo E variants have been identified. The common coding polymorphism strongly influences the lipid metabolism and the circulating concentration of apo E itself. This polymorphism is at the origin of the implication of apo E in cardiovascular and neurodegenerative diseases, but also of the relation of apo E with longevity. Probably due to its many metabolic and functional consequences, apo E polymorphism has been shown to influence the responses of patients to several drugs (fibrates, statins, hormone replacement therapy, anti-Alzheimer drugs) or environmental interventions (black tea, alcohol, diet). Apo E genotyping may be clinically helpful in defining the risk of patients and their responses to therapeutics. Finally, circulating apo E concentration appears to be altered in diseases and can be modulated by some of the drugs cited above. This parameter can thus also give interesting clinical information and could be a therapeutic target, providing it is validated. At the present time, we cannot exclude that apo E concentration may be the most prominent apo E parameter to be considered in health and disease, while apo E polymorphisms would represent only secondary parameters influencing apo E concentration.

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.