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PubMed1997

Comparison of the French and U.S. national 3H (tritiated H2O) standards by 4 pi beta liquid scintillation spectrometry.

Radioactivity standards of tritiated water (3H2O)-disseminated by the Laboratoire Primaire des Rayonnements Ionisants (LPRI) and the National Institute of Standards and Technology (NIST), the national radionuclidic metrology and standardization laboratories of France and U.S.A., respectively-have been intercompared by liquid scintillation (LS) spectrometry. The ratio of the certified massic activities for the two standards was compared to that obtained from direct measurements on matched sets of LS cocktails prepared from the standards. Seven experimental trials (involving a total of 21 counting sources for each standard) were performed for the comparison. The trials were performed under a wide range of experimental conditions, including use of two different LS spectrometers and three series of LS cocktail compositions (with systematically varied 3H detection efficiencies). The results exhibited an apparent mean disagreement between standards of < 0.4% on a relative basis. For contrast, the relative combined standard uncertainty on the massic activity ratio for the two standards, as obtained from their respective certified uncertainty assessments, is about 0.7%.

France↗
PubMed2000

Defining competency - the role of standard setting.

CONTEXT: The responsibility to determine just who is competent to practice medicine, and at what standard, is great. Whilst there is still a period available for potential remediation, examinations at the completion of year three of the four-year Graduate Entry Medical Programme (GEMP) at Flinders University of South Australia (FUSA) are high stakes and contain the majority of final summative assessment for the certification of student to doctor. Therefore, the medical school has recently examined its methods for certification, the clinical practice standards sought in its programme and how to determine these standards. DESIGN: For all assessments a standard was documented and methods employed to set these standards using specific measures of performance. A modification of the Angoff method was applied to the written examination and the Rothman method, using two criteria, was used to determine competency in the objective structured clinical examination (OSCE). These methods were used for the first time in 1998. Both methods used trained 'experts' as standard setters and both methods used the notion of the 'borderline candidate' to determine the passing standard. This paper describes these two criterion-referenced standard-setting procedures as used in this school and related examination performance. CONCLUSIONS: Whilst the use of standard-setting procedures goes part way to defining and measuring competence, it is time consuming and requires significant examiner training and acceptance. Using 50% to determine who is and isn't competent is simpler but not transparent, fair nor defensible.

Clinical Competence↗
PubMed2003

Setting standards on educational tests.

OBJECTIVE: This instalment in the series on professional assessment provides an introduction to methods of setting standards. METHOD: A standard is a special score that serves as a boundary between those who perform well enough and those who do not. The practical steps in selecting it include: deciding on the type of standard; deciding the method for setting it; selecting the judges; holding the meeting; calculating the cutpoint, and deciding what to do afterwards. Four of the more popular methods are illustrated for both written and clinical examinations. RESULTS: The most important criteria for selecting a method for setting standards are whether it is consistent with the purpose of the test, based on expert judgement, informed by data, supported by research, transparent, and requires due diligence. The credibility of the standard will rely largely on the nature of the standard setters and the selection of a broadly representative and knowledgeable group is essential. After the standard has been set, it is important to ensure that stakeholders view the results as credible and that the pass rates have sensible relationships with other markers of competence. CONCLUSIONS: A standard is an expression of professional values in the context of a test's purpose and content, the ability of the examinees, and the wider social or educational setting. Because standards are an expression of values, methods for setting them are systematic ways of gathering value judgements, reaching consensus and expressing that consensus as a single score on a test.

Clinical Competence↗
PubMed2003

A multicenter pharmacokinetic study of the B-domain deleted recombinant factor VIII concentrate using different assays and standards.

When the one-stage clotting assay is used in comparison with the chromogenic and immunological assays, plasma levels of factor (F)VIII are underestimated by 40-50% after infusion of B-domain deleted recombinant FVIII (BDD-rFVIII) in patients with hemophilia. A possible way to counteract the underestimation of FVIII levels by the one-stage assay is the adoption of a recombinant FVIII reference standard instead of a plasma standard. To evaluate the usefulness of such a standard [ReFacto Laboratory Standard (RLS)], the pharmacokinetic parameters of a single dose of BDD-rFVIII (25 U kg(-1)) were evaluated in a multicenter study carried out in 18 patients with severe hemophilia A. The very low in vivo recovery, obtained with the combination of the one-stage assay and plasma reference standard, was increased up to the values obtained by the chromogenic assay when the results were expressed in terms of RLS. When the plasma standard was used, the one-stage/chromogenic ratio was 0.82 +/- 0.12 for FVIII levels above 25 U dL(-1) and 1.42 +/- 0.99 for FVIII levels below 25 U dL(-1). Using the RLS, the one-stage/chromogenic ratio increased to 1.01 +/- 0.19 at FVIII levels above 25 U dL(-1), as a consequence of a complete overlap of the two decays; however, at FVIII levels below 25 U dL(-1), the one-stage/chromogenic ratio was still 1.6 +/- 0.85. After the twelfth hour, FVIII concentrations obtained by chromogenic assay were always lower than those resulting from the one-stage clotting assay, independently of the standard used. Results obtained by chromogenic assay were not affected by the type of standard used. Compared with those obtained by the one-stage assay, higher values of clearance, lower volume of distribution area and shorter plasma half-life or mean residence time were obtained by chromogenic assay because of a shape change of the decay curve due to a shift to higher values in the first part (time interval 0-12 h) and to lower values in the second part of the decay curve (time interval 12-48 h). As a consequence, the slope of the decay curve obtained by means of chromogenic assay was steeper. In conclusion, the more homogeneous results of in vivo recovery and pharmacokinetic analysis, due to the decrease of discrepancy between the two methods when RLS was used, make the cheaper and more widely used one-stage assay preferable to the more expensive chromogenic assay, on condition that the ReFacto specific standard has used.

Adult↗
PubMed1996

Standardization in biological analyses of aluminum: what are the needs?

A review of the literature of aluminum (Al) levels in biological samples, particularly Alzheimer's disease (AD) brain, reveals a lack of interlaboratory agreement at both the bulk and microprobe levels. One possible reason for this controversy may be the methods chosen for quantitation and standardization. Currently, the major problem affecting quantitation of Al at the bulk level is the lack of low-Al-concentration, matrix-matched certified standards. Although a number of certified aluminum bulk standards are available, most do not match well in matrix with the samples of interest. A similar situation exists for micro-probe standards in which commercially available pure metal foils and thin films of materials, such as metal oxides, are available but again do not match well in matrix. A review of the current status of quantitation of Al levels in biological analyses at the bulk and microprobe level is presented. Future directions to develop standards include the submission of currently used microprobe standards to a central laboratory for critical analysis and selection of the optimum standard, followed by establishment of interlaboratory and intertechnique comparisons. Other future directions include the adaptation of a standard protocol for the selection of tissue for analysis and criteria for data rejection, as well as the development of a standard system for data normalization and reporting.

Aluminum↗
PubMed2005

Comparison of quartz standards for X-ray diffraction analysis: HSE A9950 (Sikron F600) and NIST SRM 1878.

A further comparison of the Health and Safety Executive (HSE) standard quartz, A9950 (Sikron F600), and the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1878, standard respirable alpha-quartz, has been carried out for the four principal diffraction peaks. In the earlier comparison by Jeyaratnam and Nagar (1993, Ann Occup Hyg; 37: 167-79), the standards were both treated in ways which might change the particle size distribution and therefore the proportion of crystalline quartz. The two standards have now been compared in the most direct way possible with the minimum of sample treatment. There are no significant differences in the diffraction peak positions for the two standards. Nor do the peak area intensities differ significantly. The peak height intensities are consistently and significantly higher for Sikron F600 than for NIST SRM 1878. The particle size broadening of the diffraction peaks is evidently greater for NIST 1878, whose mass median diameter is quoted as 1.6 microm against 2.6 microm for Sikron F600. Taking the certified reference value for SRM 1878 as 95.5 +/- 1.1% crystalline quartz, the HSE standard A9950 (Sikron F600) contains 96.3 +/- 1.4% crystalline quartz based on a comparison of peak area intensities. On the same basis but using peak height intensities, the nominal crystalline quartz content of A9950 (Sikron F600) is 101.2 +/- 1.8%. Results obtained by comparison of quartz standards may not be generally applicable because of the effect of sample treatment on particle size and crystalline quartz content.

Air Pollutants, Occupational↗
PubMed2004

Genomic DNA as a cohybridization standard for mammalian microarray measurements.

A persistent design problem for ratiometric microarray studies is selecting the 'denominator' RNA cohybridization standard. The ideal standard should be readily available, inexpensive, invariant over time and from laboratory to laboratory, and should represent all genes with a uniform signal. RNA references (both commercial 'universal' and experiment--specific types), fall short of these goals. We show here that mouse genomic DNA is a reliable microarray cohybridization standard which can meet these criteria. Genomic DNA was superior in universality of coverage (>98% of genes from a 16,000 feature mouse 70mer microarray) to the Stratagene Universal Mouse Reference RNA standard. Ratios for genes in very low abundance in the Stratagene standard were more unstable with the Stratagene standard than with genomic DNA. Genes with mid-range, and therefore presumably optimal RNA denominator values, showed comparable reproducibility with both standards. Inferred ratios made between two different experimental RNAs using a genomic DNA standard were found to correlate well with companion, directly measured ratios (Spearman correlation coefficient = 0.98). The advantage in array feature coverage of genomic DNA will likely increase as newer generation microarrays include genes which are expressed exclusively in minor tissue or developmental domains that are not represented in mixed tissue RNA standards.

Animals↗
PubMed2001

Radio frequency radiation exposure standards: considerations for harmonization.

Radio frequency radiation exposure standards vary in origin, development process, legal status, and in the actual exposure limits. To identify the sources of differences in limits, we evaluated technical aspects of eight standards that included supporting information on the scientific data and rationale. Comparisons were made among the standards by examining the scope of the underlying database, the rationales for safety factors and other issues underlying exposure limits in the energy-deposition range (0.1 MHz to 10.0 GHz) and in the surface-heating range (about 10 or 15 GHz to 300 GHz). The framework for this assessment was based on the methods recommended by the scientific and regulatory organizations for developing health-based exposure limits. General guidelines for performing risk assessments for threshold acting agents have been developed by the U.S. Environmental Protection Agency, Health Canada's Environmental Health Directorate, and the International Program on Chemical Safety of the World Health Organization. This general methodology was applied to radiofrequency radiation for this assessment. Because these methods strive to identify scientific issues and separate them from risk management or policy, they provide a basis for evaluation of standards in this paper. This distinction can provide a foundation for the longer-term goal of global harmonization of radio frequency radiation standards. Each of the standards evaluated in the energy-deposition range was found to use the same basic restriction, based on biological data and a 10-fold safety factor, yet explanations reflect different interpretations of the underlying biological data. Rationales differ for the magnitude of the safety factor, for the circumstances of exposure, for the nature of sensitive populations, and for the presumed health status of the individuals for whom the basic restriction is applicable. In the surface-heating range, broad variability in exposure limits are seen in the limit itself, as well as in the approach to time averaging and frequency dependence. Averaging times differ among standards, as do tissue geometries for defining partial-body exposures. The differences in approaches to develop the standards do not completely explain differences among the exposure limits, and methods for computing exposure limits from basic restrictions are not always defined. This analysis suggests harmonization of standards will require more detailed review and coordination of biological and engineering data and of policy options.

Canada↗
PubMed2006

The effects of unfractionated heparin, low molecular weight heparin and danaparoid on the thromboelastogram (TEG): an in-vitro comparison of standard and heparinase-modified TEGs with conventional coagulation assays.

To investigate the effects of unfractionated heparin (UFH), low molecular weight heparin (LMWH) and danaparoid (DPD) added to whole blood in vitro on standard and heparinase-modified thromboelastogram (TEG) parameters compared with conventional assays of coagulation. The effects of UFH, LMWH and DPD on standard TEG parameters were compared with the prothrombin time, activated partial thromboplastin time, thrombin time and anti-activated factor X (anti-FXa) activity, at concentrations of these anticoagulants ranging from 0.025 to 1 U/ml. In the second part of the study, the effects of very low concentrations (0.005-0.05 U/ml) of UFH, LMWH and DPD on the difference between standard and heparinase-modified TEG parameters were compared with the prothrombin time, activated partial thromboplastin time, thrombin time and anti-FXa activity. Standard TEG parameters were outside the reference range at lower concentrations of UFH, LMWH and DPD than most conventional coagulation assays were able to detect. Only anti-FXa activity was more sensitive to the presence of these anticoagulants than the standard TEG alone. The lowest concentration of UFH, LMWH and DPD used in this study (0.005 U/ml) caused significant differences between the standard and heparinase-modified alpha-angles of the TEG. In addition, the difference between standard and heparinase-modified TEG parameters distinguished between low concentrations (0.005-0.05 U/ml) of UFH with greater sensitivity than anti-FXa activity, but were less sensitive to LMWH and DPD. The standard TEG is more sensitive to UFH, LMWH and DPD than most conventional coagulation tests, with the exception of anti-FXa activity. Calculation of the difference between standard and heparinase-modified TEG parameters greatly increases the sensitivity of the assay for the effects of these anticoagulants, and is more sensitive to very low quantities of UFH than anti-FXa activity.

Adult↗
PubMed2005

World Health Organization collaborative study to establish a replacement WHO international standard for hepatitis C virus RNA nucleic acid amplification technology assays.

BACKGROUND AND OBJECTIVES: A collaborative study was undertaken to establish a replacement for the current (1st) World Health Organization (WHO) hepatitis C virus (HCV) International Standard, 96/790. MATERIALS AND METHODS: Both the 1(st) International Standard and the replacement standard were prepared from the same starting material by diluting a high titre genotype 1a HCV isolate in pooled, human plasma. The only difference was that each standard was lyophilized in two, separate lyophilisation runs but under the same conditions. RESULTS: In the study to establish the 1st International Standard, no significant difference in potency was found between the material eventually designated as the 1st International Standard and that now selected as the 2nd International Standard. The present study also showed no significant differences between the materials stored at -20 degrees C and no evidence of degradation over 5 years. CONCLUSIONS: Material 96/798 was established as the 2nd HCV International Standard and assigned the same unitage as the 1st International Standard, i.e. 10(5) IU/ml (50,000 IU/vial).

DNA Primers↗
PubMed1983

A comparative analysis of birthweight for gestational age standards.

The possible consequences of the use of various birthweight-for-gestational age standards in a local population were investigated. Birthweight-for-gestational age standards based on the analysis of 55 387 births occurring to women resident in the area of the Greater Glasgow Health Board (GGHB) between 1975 and 1979 were estimated. The Glasgow based standard was then compared with a number of growth standards reported for other populations, including the widely adopted standards of Thomson et al. (1968). The relative performance of each standard when applied to the Glasgow population was assessed by calculating the sensitivity, specificity and predictive value of the various standards vis-à-vis the distribution of light-for-dates infants defined according to the Glasgow standard. The results suggest that both the accurate assessment of fetal growth at birth and the evaluation of screening procedures for antenatal detection of growth retardation require growth standards reflecting the pattern of fetal growth and development in the population at risk.

Birth Weight↗
PubMed2001

Perinatal outcome in SGA births defined by customised versus population-based birthweight standards.

OBJECTIVE: To determine whether customised birthweight standard improves the definition of small for gestational age and its association with adverse pregnancy outcomes such as stillbirth, neonatal death, or low Apgar score. DESIGN: Population based cohort study. POPULATION: Births in Sweden between 1992-95 (n = 326,377). METHODS: Risks of stillbirth, neonatal death, and Apgar score under four at five minutes were calculated for the lowest 10% birthweights according to population-based and customised standards, and were compared with the data from the group with birthweights over this limit. Population attributable risks for stillbirth using various birthweight centile cutoffs were calculated for the two standards. OUTCOME MEASURES: Odds ratios and 95% confidence intervals for stillbirth, neonatal death and Apgar score under four at five minutes, and population attributable risks for stillbirth at different birthweight centiles. RESULTS: Risks of stillbirth, neonatal death, and Apgar score under four at five minutes and population attributable risks of stillbirth were consistently higher if 'small for gestational age' was classified by a customised rather than by the population-based birthweight standard. Compared with infants who were not small for gestational age by both standards, the odds ratio for stillbirth was 6.1 (95% CI 5.0-7.5) for small for gestational age by customised standard only, whereas it was 1.2 (95 % CI 0.8-1.9) for small for gestational age by population standard only. CONCLUSIONS: Compared with the population-based birthweight standard, a customised birthweight standard increases identification of fetuses at risk of stillbirth, neonatal death and Apgar score under 4 at 5 minutes, probably due to improved identification of fetal growth restriction.

Adult↗
PubMed2005

A collaborative study to establish the 7th International Standard for Factor VIII Concentrate.

A candidate concentrate, preparation N (99/678), was assayed and calibrated, as a potential replacement, against four established factor (F) VIII concentrate standards: the current WHO 6th International Standard (IS) (97/616), the previous 5th IS (88/640), the Mega 1 standard and Ph. Eur. BRP Batch 2 standard, in a collaborative study involving 38 laboratories. All laboratories were instructed to use the ISTH/SSC recommendations, including predilution of concentrates in FVIII-deficient plasma. Several laboratories performed more than one assay method and altogether there were 27 sets of assays with the one-stage method, 31 with the chromogenic method, and 18 with both methods. There was good agreement between laboratories using each of the two methods for comparison of preparation N against the four established standards, with overall potencies by one-stage and chromogenic methods differing only by less than 2%. However, there were significant differences in potencies relative to the different standards, ranging from 10.1 IU per ampoule against the Ph. Eur.BRP2 to 11.4 against the WHO 6th IS. Accelerated degradation studies showed that the proposed standard is very stable, with a predicted loss of activity per year of less than 0.001% at the recommended storage temperature of -20 degrees C. Various options for potency of preparation N were considered by the participants and by members of the ISTH/SSC FVIII/FIX Subcommittee. In November 2003, preparation N (NIBSC 99/678) was proposed to and accepted by the Expert Committee on Biological Standardization of the World Health Organization to be the 7th International Standard for Factor VIII Concentrate with an assigned potency of 11.0 IU per ampoule.

Calibration↗
PubMed2005

A reunification of the US ("NIH") and International Unit into a single standard for Thrombin.

The existence of two different units for Thrombin in widespread international use has caused confusion for many years. The holders of the WHO International Standard (IS) for Alpha Thrombin and the US Standard (also known as the "NIH Standard") now report on a collaboration to reunite the International Unit (IU) and the US unit ("NIH unit"). A study was organised involving 25 laboratories in 15 countries to investigate the possibility of preparing a common Standard with a common unit and to investigate aspects of methodology that cause divergence of results using the IS and US Standard. Laboratories were asked to measure the potency of two candidate replacement standards (C, 01/578 and D, 01/580), and potencies were calculated relative to both the existing US Standard (lot J) and the IS (89/588). Data analysis of a total of 128 assays indicated that sample D would make an ideal replacement joint Standard with a potency of 110 IU/ampoule (equivalent to 110 US units per ampoule) based on data from clotting assays. No significant differences in results were observed using fibrinogen of human or bovine origin, or using human plasma. Comparisons of chromogenic and clotting assays indicated that sample D had a similar high proportion of alpha thrombin to the current IS for Alpha Thrombin (89/588). Sample D was adopted as the IS for Thrombin (01/580) and the US Standard (lot K) with a potency of 110 IU/ampoule.

Animals↗
PubMed2005

Agreement between diagnoses reached by clinical examination and available reference standards: a prospective study of 216 patients with lumbopelvic pain.

BACKGROUND: The tissue origin of low back pain (LBP) or referred lower extremity symptoms (LES) may be identified in about 70% of cases using advanced imaging, discography and facet or sacroiliac joint blocks. These techniques are invasive and availability varies. A clinical examination is non-invasive and widely available but its validity is questioned. Diagnostic studies usually examine single tests in relation to single reference standards, yet in clinical practice, clinicians use multiple tests and select from a range of possible diagnoses. There is a need for studies that evaluate the diagnostic performance of clinical diagnoses against available reference standards. METHODS: We compared blinded clinical diagnoses with diagnoses based on available reference standards for known causes of LBP or LES such as discography, facet, sacroiliac or hip joint blocks, epidurals injections, advanced imaging studies or any combination of these tests. A prospective, blinded validity design was employed. Physiotherapists examined consecutive patients with chronic lumbopelvic pain and/or referred LES scheduled to receive the reference standard examinations. When diagnoses were in complete agreement regardless of complexity, "exact" agreement was recorded. When the clinical diagnosis was included within the reference standard diagnoses, "clinical agreement" was recorded. The proportional chance criterion (PCC) statistic was used to estimate agreement on multiple diagnostic possibilities because it accounts for the prevalence of individual categories in the sample. The kappa statistic was used to estimate agreement on six pathoanatomic diagnoses. RESULTS: In a sample of chronic LBP patients (n = 216) with high levels of disability and distress, 67% received a patho-anatomic diagnosis based on available reference standards, and 10% had more than one tissue origin of pain identified. For 27 diagnostic categories and combinations, chance clinical agreement (PCC) was estimated at 13%. "Exact" agreement between clinical and reference standard diagnoses was 32% and "clinical agreement" 51%. For six pathoanatomic categories (disc, facet joint, sacroiliac joint, hip joint, nerve root and spinal stenosis), PCC was 33% with actual agreement 56%. There was no overlap of 95% confidence intervals on any comparison. Diagnostic agreement on the six most common patho-anatomic categories produced a kappa of 0.31. CONCLUSION: Clinical diagnoses agree with reference standards diagnoses more often than chance. Using available reference standards, most patients can have a tissue source of pain identified.

Humans↗
PubMed2002

Calibration of the Ph. Eur. BRP Batch 3/Mega 2 (US/FDA) standard for human coagulation factor VIII concentrate for use in the potency assay.

The European Pharmacopoeia Biological Reference Preparation Batch 3/Mega 2 (United States/Food and Drug Administration) (Ph. Eur. BRP Batch 3/Mega 2 (US/FDA)) was developed as an internationally available, common working standard to replace the dwindling stocks of Mega 1 (the current US standard) and Ph. Eur. BRP Batch 2 (the current European standard). The potency was assigned in an international collaborative study with reference to four currently established standards, Ph. Eur. BRP batch 2, WHO 5th and 6th International Standard and Mega 1. Thirty-eight laboratories participated in the collaborative study. Each laboratory was asked to perform four independent assays. Participants used either the one stage clotting assay or the chromogenic assay or both. This publication reports the results obtained with both assays. The summary and conclusion, however highlight the results mainly with respect to the chromogenic assay, which is the assay prescribed in the European Pharmacopoeia. Data were analysed for both assays separately. A consensus potency value was calculated as the unweighted average of mean potencies determined against the four standards. A potency of 8.6 IU/vial as determined in the chromogenic substrate method was assigned to the candidate standard. Inter-laboratory agreement as assessed by calculation of the geometric coefficient of variation was below 10% for mean potencies against all four calibrators for the chromogenic assay. Ph. Eur. BRP Batch 3/Mega 2 (US/FDA) is a freeze-dried, plasma derived, high-purity concentrate. The material was filled into approximately 100,000 vials and lyophilised to a final residual moisture of < or = 2%. Approximately 90,000 vials of the standard are available, equally shared between the two co-ordinating centers. Based on the stability studies, the predicted mean percentage loss per year at -20 degrees C is 0.000% and thus the candidate standard appears to be stable. The Ph. Eur. BRP batch 3 was adopted by the European Pharmacopoeia Commission in November 2001.

Blood Coagulation Tests↗
PubMed1953

The international standard for bacitracin.

In 1952, the Department of Biological Standards, National Institute for Medical Research, London, was authorized by the WHO Expert Committee on Biological Standardization to proceed with the establishment of an International Standard for Bacitracin. Thirty grams of bacitracin were obtained and it was decided to compare the proposed International Standard with the existing Working Standard for Bacitracin of the United States Food and Drug Administration.Six laboratories in five countries participated in the collaborative assay. A total of 52 assays was carried out, but the overall weighted mean potency was calculated from only the 48 biological assays, the 4 assays by the Hiscox method being excluded. The biological assays were done by the plate, the cylinder, or the disc method, using Streptococcus pyogenes, Staphylococcus aureus, Corynebacterium xerosis, or Micrococcus flavus.After analysing the results by standard statistical methods, the authors established the batch of bacitracin examined as the International Standard. The Standard contains 55 International Units of activity per mg, and the International Unit has therefore been defined as the activity contained in 0.0182 mg of the International Standard for Bacitracin.

Bacitracin↗
PubMed1962

The Third International Standard for Corticotrophin.

At its meeting in September 1957, the WHO Expert Committee on Biological Standardization agreed with the recommendation of the International Conference on Corticotrophin, held in July 1957, that a new international standard for corticotrophin should be set up, since the Second International Standard was made from crude material and was unsuitable for the assay of the purer preparations of corticotrophin now in general clinical use. In this paper, the authors describe the steps taken to establish the Third International Standard for Corticotrophin, from the preparation and international collaborative assay of the new material to the choice of the "subcutaneous assay" for deriving the potency. The clinical and pharmacological implications of this choice are discussed.Since the preparation, characterization and exact quantitative assay of standards for corticotrophin are so difficult, several batches of approximately 3500 ampoules were prepared in a similar way from the same material to serve as an international Working Standard. Samples from two batches were included in the collaborative assay and found to have the same potency as the Third Standard. Sufficient ampoules of the Working Standard are available for use as national and laboratory standards.

Adrenocorticotropic Hormone↗