Functional reference limits: a case study of serum ferritin

Abstract Reference intervals depend on the distribution of results within a reference population and can be influenced by subclinical disease. Functional reference limits present an opportunity to derive clinically relevant reference limits from routinely collected data sources, which consist of mixed populations of unhealthy and healthy groups. Serum ferritin is a good example of the utility of functional reference limits. Several studies have identified clinically relevant reference limits through examining the relationship between serum ferritin and erythrocyte parameters. These ferritin functional limits often represent the inflection point at which erythrocyte parameters change significantly. Comparison of ferritin functional reference limits with those based on population distributional reference limits reveals that the lower reference limit may fall below the point at which patients become clinically unwell. Functional reference limits may be considered for any biomarker that exhibits a correlated relationship with other biomarkers.

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Impact of Subgroup Prevalences on Partitioning of Gaussian-distributed Reference Values

Clinical Chemistry ◽

10.1093/clinchem/48.11.1987 ◽

2002 ◽

Vol 48 (11) ◽

pp. 1987-1999 ◽

Cited By ~ 49

Author(s):

Ari Lahti ◽

Per Hyltoft Petersen ◽

James C Boyd

Keyword(s):

Reference Interval ◽

Reference Population ◽

Reference Intervals ◽

Source Population ◽

Distributed Data ◽

New Model ◽

Common Reference ◽

Reference Limits ◽

Partitioning Problem ◽

Analytical Expressions

Abstract Background: The aims of this report were to examine how unequal subgroup prevalences in the source population may affect reference interval partitioning decisions and to develop generally applicable guidelines for partitioning gaussian-distributed data. Methods: We recently proposed a new model for partitioning reference intervals when the underlying data distribution is gaussian. This model is based on controlling the proportions of the subgroup distributions that fall outside each of the common reference limits, using the distances between the reference limits of the subgroup distributions as functions to these proportions. We examine the significance of the unequal prevalence effect for the partitioning problem and quantify it for distance partitioning criteria by deriving analytical expressions to express these criteria as a function of the ratio of prevalences. An application example, illustrating various aspects of the importance of the prevalence effect, is also presented. Results: Dramatic shrinkage of the critical distances between reference limits of the subgroups needed for partitioning was observed as the ratio of prevalences, the larger one divided by the smaller one, was increased from unity. Because of this shrinkage, the same critical distances are not valid for all ratios of prevalences, but specific critical distances should be used for each particular value of this ratio. Although proportion criteria used in determining the need for reference interval partitioning are not dependent on the prevalence effect, this effect should be accounted for when these criteria are being applied by adjusting the sample sizes of the subgroups to make them correspond to the ratio of prevalences. Conclusions: The prevalences of subgroups in the reference population should be known and observed in the calculations for every reference interval study, irrespective of whether distance or proportion criteria are being used to determine the need for reference interval partitioning. We present detailed methods to account for the prevalences when applying each of these types of criteria. Analytical expressions for the distance criteria, to be used when high precision is needed, and approximate distances, to be used in practical work, are derived. General guidelines for partitioning gaussian distributed data are presented. Following these guidelines and using the new model, we suggest that partitioning can be performed more reliably than with any of the earlier models because the new model not only offers an improved correspondence between the critical distances and the critical proportions, but also accounts for the prevalence effect.

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Albumin and calcium reference interval using healthy individuals and a data-mining approach

Annals of Clinical Biochemistry International Journal of Laboratory Medicine ◽

10.1177/0004563220944204 ◽

2020 ◽

Vol 57 (5) ◽

pp. 373-381 ◽

Cited By ~ 2

Author(s):

N Jassam ◽

A Luvai ◽

D Narayanan ◽

D Turnock ◽

G Lee ◽

...

Keyword(s):

Metrological Traceability ◽

Reference Interval ◽

Reference Population ◽

Reference Intervals ◽

Healthy Individuals ◽

Reference Limit ◽

Common Reference ◽

Age Related ◽

Upper Reference Limit ◽

Analytical Platforms

Background Harmonization of reference intervals for analytes that have a sound calibration and metrological traceability is a widely recommended practice. The UK Pathology Harmony has recently harmonized reference intervals for calcium and albumin. In this study, we have determined the reference intervals for calcium and albumin on the UK’s most commonly used analytical platforms. Method A prospective reference population of healthy individuals was recruited according to the IFCC CRIDL criteria. A second indirect population was collected from 14 primary care setting and measured in laboratories using various analytical platforms and methods (Roche, Abbott, Beckman and Siemens analytical platforms). Results In total, 299 subjects were recruited; the central 95th centile values for calcium for three out of four analytical platforms were in a close agreement with UK Pathology Harmony reference intervals of 2.2–2.6 mmol/L. Reference intervals of BCG methods from both cohorts and irrespective of analytical platforms were higher for both lower and upper reference limits than those for BCP. In comparison, the indirect study showed an age-related variation. The younger population reference intervals varied by up to 5.7% at the lower reference limit and up to 12% at the upper reference limit compared with Pathology Harmony reference intervals, and the older population showed a variation of up to 14% at both limits. Conclusion While calcium reference intervals can be a subject for harmonization, albumin reference intervals studied showed large variation which is unsupportive of embracing a common reference interval for albumin.

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Recommendation for the review of biological reference intervals in medical laboratories

Clinical Chemistry and Laboratory Medicine (CCLM) ◽

10.1515/cclm-2016-0793 ◽

2016 ◽

Vol 54 (12) ◽

Cited By ~ 22

Author(s):

Joseph Henny ◽

Anne Vassault ◽

Guilaine Boursier ◽

Ines Vukasovic ◽

Pika Mesko Brguljan ◽

...

Keyword(s):

Expert Panel ◽

Clinical Chemistry ◽

Simple Procedure ◽

Reference Population ◽

Reference Intervals ◽

Medical Laboratories ◽

Reference Limits ◽

Original Procedure ◽

Selection Of

AbstractThis document is based on the original recommendation of the Expert Panel on the Theory of Reference Values of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), updated guidelines were recently published under the auspices of the IFCC and the Clinical and Laboratory Standards Institute (CLSI). This document summarizes proposals for recommendations on: (i) The terminology, which is often confusing, noticeably concerning the terms of reference limits and decision limits. (ii) The method for the determination of reference limits according to the original procedure and the conditions, which should be used. (iii) A simple procedure allowing the medical laboratories to fulfill the requirements of the regulation and standards. The updated document proposes to verify that published reference limits are applicable to the laboratory involved. Finally, the strengths and limits of the revised recommendations (especially the selection of the reference population, the maintenance of the analytical quality, the choice of the statistical method used…) will be briefly discussed.

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Objective Criteria for Partitioning Gaussian-distributed Reference Values into Subgroups

Clinical Chemistry ◽

10.1093/clinchem/48.2.338 ◽

2002 ◽

Vol 48 (2) ◽

pp. 338-352 ◽

Cited By ~ 31

Author(s):

Ari Lahti ◽

Per Hyltoft Petersen ◽

James C Boyd ◽

Callum G Fraser ◽

Nils Jørgensen

Keyword(s):

Reference Values ◽

Geographic Area ◽

Reference Intervals ◽

Critical Values ◽

Final Decision ◽

Gaussian Distributions ◽

New Model ◽

Reference Limit ◽

Common Reference ◽

Reference Limits

Abstract Background: The aim of this study was to develop new and useful criteria for partitioning reference values into subgroups applicable to gaussian distributions and to distributions that can be transformed to gaussian distributions. Methods: The proposed criteria relate to percentages of the subgroups outside each of the reference limits of the combined distribution. Critical values suggested as partitioning criteria for these percentages were derived from analytical bias quality specifications for using common reference intervals throughout a geographic area. As alternative partitioning criteria to the actual percentages, these were transformed mathematically to critical distances between the reference limits of the subgroup distributions, to be applied to each pair of reference limits, the upper and the lower, at a time. The new criteria were tested using data on various plasma proteins collected from ∼500 reference individuals, and the outcomes were compared with those given by the currently widely applied and recommended partitioning model of Harris and Boyd, the “Harris-Boyd model”. Results: We suggest 4.1% as the critical minimum percentage outside that would justify partitioning into subgroups, and 3.2% as the critical maximum percentage outside that would justify combining them. Percentages between these two values should be classified as marginal, implying that nonstatistical considerations are required to make the final decision on partitioning. The correlation between the critical percentages and the critical distances was mathematically precise in the new model, whereas this correlation is rather approximate in the Harris-Boyd model because focus on the difference between means in this model makes high precision hard to achieve. The application examples suggested that the new model is more radical than the Harris-Boyd model. Conclusions: New percentage and distance criteria, to be used for partitioning gaussian-distributed data, have been developed. The distance criteria, applied separately to both reference limit pairs of the subgroup distributions, seemed more reliable and correlated more accurately with the critical percentages than the distance criteria of the Harris-Boyd model. As opposed to the Harris-Boyd model, the new model is easily adjustable to new critical values of the percentages, should they need to be changed in the future.

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A self-consistent set of reference values for 23 clinical chemical analytes.

Clinical Chemistry ◽

10.1093/clinchem/35.3.448 ◽

1989 ◽

Vol 35 (3) ◽

pp. 448-452 ◽

Cited By ~ 3

Author(s):

U E Spichiger ◽

D J Vonderschmitt

Keyword(s):

Reference Values ◽

Iterative Procedure ◽

Blood Donors ◽

Reference Population ◽

Reference Intervals ◽

Men And Women ◽

A Value ◽

Self Consistent ◽

Reference Limits ◽

Clinical Chemical

Abstract Heparinized plasma of 528 blood donors was subjected to the 23 most frequently ordered chemical and enzymatic tests. The central fraction of the distribution of all results for each test was estimated. Out of the 528 donors a reference population has been selected. Because of the lack of other criteria, the result for any test of a blood donor was selected as a value belonging to the reference population if the results for the other 22 analytes of this particular donor lay within their own central fraction. On this basis an iterative procedure for the selection was programmed, considering the interaction between tests. The procedure was stopped when the reference limits for all 23 tests were converging. Fractions from 0.90 to 0.98 were applied to results for men and women donors separately. The elimination procedure and the criteria to select the best fitted fraction are discussed. The derived reference intervals are designated a "self-consistent set of reference values."

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Equivalence limits of reference intervals for partitioning of population data. Relevant differences of reference limits

LaboratoriumsMedizin ◽

10.1515/labmed-2016-0002 ◽

2016 ◽

Vol 40 (3) ◽

Author(s):

Rainer Haeckel ◽

Werner Wosniok ◽

Farhad Arzideh

Keyword(s):

Population Data ◽

Reference Intervals ◽

International Standards ◽

Reference Limit ◽

Permissible Limits ◽

First Case ◽

Reference Limits ◽

External Sources ◽

The Difference ◽

Simple Equations

Abstract:Reference limits need to be compared with each other for two main purposes: to evaluate the clinical relevance of a possible difference, if limits are obtained from the same population but at different time periods, or to check if limits derived from two different subpopulations can be considered as identical. The comparison of reference limits required for the periodic reviewing of applied reference limits and for checking the transferability of reference limits adopted from external sources according to international standards is an example for the first case. In the second case, a decision is intended whether the full population has to be partitioned (stratified) into the subpopulations under consideration (e.g. males and females). In both situations, differences may be due either to analytical errors, to biological differences or to both effects. The difference between reference limits may be acceptable if it is within permissible limits. For establishing permissible limits, the concept of equivalence limits was adopted to assess the relevance of differences between two reference limits. The concept bases on the permissible uncertainty at a particular reference limit. The permissible uncertainty is quantified by the permissible analytical standard deviation derived from the empirical biological variation as recently proposed. It is defined separately for lower and upper reference limits. The concept proposed can be condensed to simple equations.

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RIA for Serum Holo-Transcobalamin: Method Evaluation in the Clinical Laboratory and Reference Interval

Clinical Chemistry ◽

10.1373/49.3.455 ◽

2003 ◽

Vol 49 (3) ◽

pp. 455-462 ◽

Cited By ~ 40

Author(s):

Saila Loikas ◽

Minna Löppönen ◽

Pauli Suominen ◽

Jan Møller ◽

Kerttu Irjala ◽

...

Keyword(s):

Biochemical Markers ◽

Methylmalonic Acid ◽

Clinical Laboratory ◽

Reference Interval ◽

Reference Population ◽

Reference Intervals ◽

Method Evaluation ◽

Elderly Individuals ◽

Reference Limit ◽

Total Homocysteine

Abstract Background: Decreased serum holo-transcobalamin (holoTC) could be the earliest marker of cobalamin (Cbl) deficiency, but there has been no method suitable for routine use. We evaluated a new commercial holoTC RIA, determined reference values, and assessed holoTC concentrations in relation to other biochemical markers of Cbl deficiency. Methods: The reference population consisted of 303 individuals 22–88 years of age, without disease or medication affecting Cbl or homocysteine metabolism. In elderly individuals (≥65 years), normal Cbl status was further confirmed by total homocysteine (tHcy; <19 μmol/L) and methylmalonic acid (MMA; <0.28 μmol/L) concentrations within established reference intervals. HoloTC in Cbl deficiency was studied in a population of 107 elderly individuals with normal renal function. The Cbl deficiency was graded as potential (total Cbl ≤150 pmol/L or tHcy ≥19 μmol/L), possible (total Cbl ≤150 pmol/L and either tHcy ≥19 μmol/L or MMA ≥0.45 μmol/L), and probable (tHcy ≥19 μmol/L and MMA ≥0.45 μmol/L). Results: The intra- and between-assay imprecision (CV) for the holoTC RIA were 4–7% and 6–8%, respectively. A 95% central reference interval for serum holoTC was 37–171 pmol/L. All participants (n = 16) with probable Cbl deficiency, 86% of those with possible, and 30% of those with potential Cbl deficiency had holoTC below the reference limit (<37 pmol/L). The holoTC correlated with total Cbl (rs = 0.80; P <0.0001) and inversely with MMA (rs = −0.52; P <0.0001). HoloTC concentrations were significantly (P = 0.01) higher in women than in men. Conclusions: The new holoTC RIA is precise and simple to perform. Low holoTC is found in individuals with biochemical signs of Cbl deficiency, but the sensitivity and specificity of low holoTC in diagnosis of Cbl deficiency need to be further evaluated.

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Cerebrospinal fluid tau and Aβ42 concentrations in healthy subjects: delineation of reference intervals and their limitations

Clinical Chemistry and Laboratory Medicine (CCLM) ◽

10.1515/cclm.2004.071 ◽

2004 ◽

Vol 42 (4) ◽

Cited By ~ 8

Author(s):

Pierre R. Burkhard ◽

Roxane Fournier ◽

Bernadette Mermillod ◽

Karl-Heinz Krause ◽

Constantin Bouras ◽

...

Keyword(s):

Cerebrospinal Fluid ◽

Healthy Adult ◽

Reference Population ◽

Reference Intervals ◽

Inclusion Criteria ◽

Dementia Patients ◽

Large Numbers ◽

Reference Limits ◽

Neurologically Intact

AbstractMany limitations and conflicting results have cast serious doubts on the validity of cerebrospinal fluid tau and Aβ42 levels for the biological diagnosis of Alzheimer's disease, particularly extreme variations of the reference limits found by unrelated groups as a consequence of different reference populations used. In this study, we addressed the issue of defining reference limits for cerebrospinal fluid tau and Aβ42 in healthy adult individuals. One hundred and five neurologically intact subjects were enrolled according to strict inclusion criteria, 10 of them with autopsy confirmation of brain integrity. All cerebrospinal fluid samples were similarly and optimally processed as were the dosage methods used and the statistical analyses performed. A robust correlation with age was demonstrated for Aβ42 but not for tau. For tau, we found that an upper cut-off value of 443 ng/l allowed 95% of the subjects to be correctly classified as normal. For Aβ42, a lower cut-off value of 90 ng/l allowed a correct classification of 90% of the subjects. However, a large variance of the reference values, partly explained by the potential contamination of the reference population with presymptomatic dementia patients, may limit the use of reference limits based on living subjects. We propose that the issue of defining reference limits for both cerebrospinal fluid tau and Aβ42 may ultimately be settled by studying large numbers of autopsy-proven neurologically intact individuals only.

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Reference intervals of salivary cortisol and cortisone and their diagnostic accuracy in Cushing’s syndrome

Acta Endocrinologica ◽

10.1530/eje-19-0872 ◽

2020 ◽

Vol 182 (6) ◽

pp. 569-582 ◽

Cited By ~ 1

Author(s):

Nils Bäcklund ◽

Göran Brattsand ◽

Marlen Israelsson ◽

Oskar Ragnarsson ◽

Pia Burman ◽

...

Keyword(s):

Diagnostic Accuracy ◽

Cushing’S Syndrome ◽

Salivary Cortisol ◽

Reference Population ◽

Reference Intervals ◽

Cushing's Syndrome ◽

Late Night ◽

Reference Limits ◽

Liquid Chromatography Tandem Mass ◽

Design And Methods

Objective The challenge of diagnosing Cushing’s syndrome (CS) calls for high precision biochemical screening. This study aimed to establish robust reference intervals for, and compare the diagnostic accuracy of, salivary cortisol and cortisone in late-night samples and after a low-dose (1 mg) dexamethasone suppression test (DST). Design and methods Saliva samples were collected at 08:00 and 23:00 h, and at 08:00 h, after a DST, from 22 patients with CS and from 155 adult reference subjects. We also collected samples at 20:00 and 22:00 h from 78 of the reference subjects. Salivary cortisol and cortisone were analysed with liquid chromatography-tandem mass spectrometry. The reference intervals were calculated as the 2.5th and 97.5th percentiles of the reference population measurements. Diagnostic accuracies of different tests were compared, based on areas under the receiver-operating characteristic curves. Results The upper reference limits of salivary cortisol and cortisone at 23:00 h were 3.6 nmol/L and 13.5 nmol/L, respectively. Using these reference limits, CS was detected with a sensitivity (95% CI) of 90% (70–99%) and specificity of 96% (91–98%) for cortisol, and a 100% (84–100%) sensitivity and 95% (90–98%) specificity for cortisone. After DST, cortisol and cortisone upper reference limits were 0.79 nmol/L and 3.5 nmol/L, respectively. CS was detected with 95% (75–100%) sensitivity and 96% (92–99%) specificity with cortisol, and 100% (83–100%) sensitivity and 94% (89–97%) specificity with cortisone. No differences in salivary cortisol or cortisone levels were found between samples collected at 22:00 and 23:00 h. Conclusion Salivary cortisol and cortisone in late-night samples and after DST showed high accuracy for diagnosing CS, salivary cortisone being slightly, but significantly better.

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Calculation of indirect reference intervals of plasma lipase activity of adults from existing laboratory data based on the Reference Limit Estimator integrated in the OPUS::L information system

Journal of Laboratory Medicine ◽

10.1515/labmed-2021-0008 ◽

2021 ◽

Vol 45 (2) ◽

pp. 131-134

Author(s):

Britta Amodeo ◽

Aline Schindler ◽

Ulrike Schacht ◽

Hans Günther Wahl

Keyword(s):

Information System ◽

Lipase Activity ◽

Clinical Chemistry ◽

Laboratory Data ◽

Direct Methods ◽

Reference Interval ◽

Reference Intervals ◽

Specific Reference ◽

Reference Limit ◽

Reference Limits

Abstract Objectives Most laboratories have difficulties to determine their own reference intervals for the diagnostic evaluation of patient results by direct methods. Therefore, data is often just taken from the literature or package inserts of the analytical tests. Methods The section on Reference Limits of the German Society for Clinical Chemistry and Laboratory Medicine (DGKL) first uploaded the Reference Limit Estimator (RLE) as an R-program with MS Excel-interface on the DGKL home page and now this tool is implemented in the commercial Laboratory Information System OPUS::L (OSM AG Essen, Germany). We used this OPUS::L “Population specific Reference Limits” tool online with our laboratory database. First calculations were done using the example of lipase. Results The manufacturer’s original reference interval for lipase 12–53 U/L (adults) was changed to age dependent upper reference limits of <41 U/L (<20 years), <60 U/L (20–80 years) and <70 U/L (>80 years). Conclusions By means of the OPUS::L “Population specific Reference Limits” tool we were able to establish our laborarotry specific reference interval for plasma lipase activity. The new reference limits helped to solve an old problem of implausible low elevated lipase values.

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