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PubMed1989

Characterization of instrumentation and calibrators for quantitative microfluorometry for immunofluorescence tests.

The current method for measuring reagents for immunofluorescence microscopy involves a subjective evaluation of the endpoint (titer) with a negative or positive (1+ to 4+) scale. Variability is due to the biological constituents of the reagent, the observer, and the instrumentation. To have reliable methods for evaluation of performance of these products, we are developing a quantitative method that uses photometric measurements of microscopically observed epifluorescence of slide preparations. A computer-controlled microscope-photometer converts the light intensity into a voltage measurement. Our goal is to replace the subjective endpoint determination with an objective, quantitative method. The instrumentation and its operating characteristics are presented in this paper. Selected commercially available fluorescent materials were evaluated as calibrators for the instrumentation. These materials showed consistency in measurement and thus demonstrated their suitability for various levels of calibration. It is possible that they will prove useful as a reference standard for interlaboratory comparisons.

Cytophotometry↗
PubMed2005

Characterization of allergen extracts.

Allergen vaccines are complex extracts of natural products, and are used for the diagnosis and treatment of allergic diseases. In the U.S., 19 allergen extracts have been standardized. For these vaccines, the potency is estimated by the skin test responses of highly allergic individuals, and surrogate in vitro tests are established for lot release and quality control. The surrogate tests differ for different extracts. National reference standards to which manufactured lots are compared are maintained at FDA/CBER. Allergen standardization has facilitated the establishment of data-driven release limits.

Allergens↗
PubMed1994

Multicenter comparison of Neisseria meningitidis serogroup C anti-capsular polysaccharide antibody levels measured by a standardized enzyme-linked immunosorbent assay.

A standardized enzyme-linked immunosorbent assay (ELISA) was used by 11 laboratories to measure levels of total serum antibody to Neisseria meningitidis serogroup C capsular polysaccharide in 16 unpaired pre- and postvaccination serum samples. Twelve serum samples were from adults, and four were from children aged 2, 3, 5, and 9. The between-laboratory coefficient of variation for pre- and postvaccination sera ranged from 16 to 59% and 11 to 21%, respectively. The average percent difference (absolute value) from the between-laboratory means for all prevaccination sera measured by each laboratory was 24%, whereas the average percent difference was 13% for all postvaccination sera. A postvaccination quality control serum was diluted three times to give optical densities on the high, middle, and low portions of the standard reference curve. The three dilutions were assayed by the 11 laboratories a total of 241 times and yielded an overall coefficient of variation of 20%. Antibody-binding inhibition curves showed that the standardized ELISA was specific for N. meningitidis serogroup C capsular polysaccharide antibody. Fifty percent inhibition of seven serum samples was obtained after reaction with an average concentration of 0.9 micrograms of meningococcal serogroup C polysaccharide per ml; an average of 93% inhibition was obtained with 50 micrograms of polysaccharide per ml. The acceptance and use of this standardized ELISA will reduce between-laboratory assay variability and ensure a more accurate and reproducible assessment of immunogenicity for vaccines under development.

Adult↗
PubMed1986

Quality control of azure B preparations by liquid chromatography and standardization with azure B tetrafluoroborate.

A liquid chromatographic procedure for the quantitative determination of the thiazine dye azure B, the principal constituent of Romanowsky stains, is presented. Unlike previous methods relying on peak area normalization, the present approach involves real quantitation through calibration with the reference standard azure B tetrafluoroborate. The method has been used for the quality control of commercial azure B preparations and to study their stability in stock and staining solutions, either or not in the presence of eosin Y. Results suggest that highly pure azure B perchlorate meets the requirements of a reference material, useful for standardization of Romanowsky-Giemsa staining in haematology.

Azure Stains↗
PubMed2003

Establishment of traceability of ammonium nitrogen determination in wastewater.

A case study is presented for the establishment of traceability for ammonium nitrogen determination in wastewater in a routine laboratory in order to fulfil the requirements of ISO/IEC standard 17025. The necessary relevant information was obtained from the method validation data, the quality control data and equipment calibration certificates. The method of measurement is described together with the measurement equation, selected traceable reference standards and the associated measurement uncertainty. The major sources of uncertainty of the result of measurement were identified and the combined uncertainty was calculated. Identification of the main uncertainty sources represents the basis for target operations for reducing the measurement uncertainty of this determination.

Calibration↗
PubMed1997

Standards for radioiodines.

The National Institute of Standards and Technology, NIST (formerly National Bureau of Standards), is the nation's standards laboratory for civilian technology. NIST develops and maintains the nation's physical measurement standards for medical therapy and diagnostics. For the past 50 years, NIST has developed radioactivity Standard Reference Materials (SRMs) for radioiodines as well as decay-scheme data and test methods for use by the radiopharmaceutical manufacturers in their quality assurance and quality control at the point of manufacture. Methods of standardizing radioiodines include 4 pi beta-gamma coincidence counting (131I), 4 pi beta-gamma anti-coincidence counting (129I), 4 pi(e,x)-gamma coincidence counting (123I), and x-gamma sum peak coincidence counting (125I). NIST also uses sources standardized by these techniques to calibrate re-entrant ionization chambers (dose calibrators) and scintillation counters. SRMs of 131I and 125I are now available on an annual basis, and the long-lived 129I has recently been reissued.

Iodine Radioisotopes↗
PubMed1996

Gas chromatography-mass spectrometry identification of a novel N3-methylated metabolite of 5'-deoxy-5-fluorouridine in plasma of cancer patients undergoing chemotherapy.

Evidence of in vivo biomethylation of the anticancer pro-drug 5'-deoxy-5-fluorouridine (5'-dFUR) is presented for the first time. Biomethylation seems to occur specifically at the N3 site on the pyrimidine ring. This novel metabolic product was detected by gas chromatography-mass spectrometry of the trimethylsilylated extract of plasma samples from cancer patients undergoing doxifluridine chemotherapy. Considering the observed electron impact fragmentation pattern, the metabolic product was tentatively identified as N3-Me-5'-dFUR. Definite confirmation of the proposed structure was achieved by comparison of the mass spectra and chromatographic characteristics of the suspected metabolite with those of a synthetically prepared reference standard.

Antineoplastic Agents↗
PubMed2000

Feasibility of using lignin isolated from forages by solubilization in acetyl bromide as a standard for lignin analyses.

Lignin concentration can be measured in plants by the acetyl bromide-soluble lignin spectrophotometric method; however, as with any spectrophotometric method, a reliable standard is needed. In the present experiments, lignin was extracted from each of the forages under study with the acetyl bromide reagent. The lignin isolated with acetyl bromide (LIAB) was then used as the reference standard in the acetyl bromide-soluble lignin (ABSL) analysis, which was compared with the acid detergent lignin (ADL) and potassium permanganate lignin (PerL) lignin analyses. Two maturity stages of each of the following forages were analyzed: Medicago sativa, Cynodon dactylon var. Coastal, Panicum maximum var. Centenário and var. Colonião, Cynodon plectostachyus, Pennisetum purpureum, Setaria nandi, and Avena sativa. In addition, one wood sample, Eucalyptus sp., was analyzed. In general, ABSL values were highest (P < 0.001), followed by PerL and ADL, which also differed from each other (P < 0.001). Correlations with in vitro dry matter digestibility of samples were highest with the ABSL method. Absorption spectra of LIAB, either from plants of different maturity stages or from different vegetable species, suggested the presence of differences among some of the lignins.

Acetates↗
PubMed1999

Theory and practice of cytokine assessment in immunotoxicology.

The tools and concepts of immunotoxicology are increasingly being used in novel ways, such as using toxic reagents to understand immune system function. One of the most potentially useful of these new tools is the assessment of cytokines, the molecules responsible for regulating a variety of processes including immunity, inflammation, apoptosis, and hematopoiesis. Cytokine production or bioactivity may be affected by a variety of toxic mechanisms including direct toxicity to cytokine-producing cells, inhibition of cytokine production, inhibition of cytokine release, induction of immunosuppressive factors, alterations in cellular homeostasis, alterations in cellular activational or transcriptional mechanisms, and miscellaneous or undefined mechanisms. Moreover, alterations in the profile of cytokine production may provide important information regarding the nature of an immunotoxic insult (i.e., TH1 vs TH2 response). Proper evaluation of the role of cytokine modulation in immunotoxicology requires attention to myriad details. Some of the details discussed in this review include the source of the sample to be tested (circulating, local, or ex vivo isolated cells); the potential effects of collection, processing, and storage on the results of the assays; potential variables associated with the source material (matrix effects, relevance, inhibitory substances); and factors influencing the choice of assay used (bioassay, immunoassay, molecular biology technique, flow cytometry, hybrid assays). Other often-overlooked issues are discussed, including species considerations and quality control issues such as the use of reference standards and the expression of results.

Animals↗
PubMed2005

Chemical fingerprinting of Isatis indigotica root by RP-HPLC and hierarchical clustering analysis.

The aim was to establish a method for extraction and chemical fingerprinting of extracts of Isatis indigotica roots ("Ban-Lan-Gen") and to apply the method developed to 18 Ban-Lan-Gen samples. RP-HPLC with gradient elution was performed on authentic reference standards of powdered I. indigotica roots, indigotin and indirubin purchased from the National Institute for the Control of Pharmaceutical and Biological Products (NICPBP) of China. Eighteen "Ban-Lan-Gen" samples (including the reference powdered herb) were bought from Singapore and different regions in China. Comparisons of the chromatograms showed that the samples can be divided into three groups. The chromatograms of the extracts of five samples were found to be similar to that of the extract of the authentic sample. Eight other samples had similar peaks as the authentic sample but the intensities of the peaks were generally lower, except for the peaks between retention times of 10-40 min. Peaks in these regions were more intense than those found in the extract of the authentic sample. Forty-five characteristic peaks could be found in the extracts of all the above samples. Peaks at retention times 52 and 53 min were determined to be indigotin and indirubin, respectively. The remaining four samples had similar chemical fingerprints to each other but were different from that of the authentic sample. Hierarchical clustering analysis gave similar results as the visual comparison. The RP-HPLC method developed allows simple identification and comparisons of I. indigotica roots. This is the first report of hierarchical clustering analysis of I. indigotica root.

Chromatography, High Pressure Liquid↗
PubMed1999

International standards for growth hormone.

Since 1955, with the establishment by the World Health Organization of the first International Standard (IS) for bovine growth hormone (GH) for bioassay, there have been a number of developments in the standardization of GH. Two GH ISs are in current use: the IS for human GH established in 1982 and the IS for somatropin (recombinant DNA-derived GH) established in 1994. The availability of two such standards does not encourage reproducibility of GH estimates between different laboratories. The author proposes that the international validation and adoption of the IS for somatropin, which has the advantage of an internationally agreed specific activity of 3 IU/mg, as the primary reference standard for all GH immunoassays would finally eliminate this source of variation in GH estimates.

Animals↗
PubMed1983

An historical review of quality control in hematology.

As the use of laboratory techniques in diagnostic medicine increase, it became obvious that standardized reference methods and stable controls were essential in order for results obtained in different laboratories to be comparable. Certain procedures and standards have been adopted to provide QC in hematology. Currently procedures include the following: cyanmethemoglobin for HGB determinations; particle counter for RBC and WBC counts; phase microscopy for PLT counts; and packed cell volume for HCT determinations. These serve as acceptable reference methods for multichannel hematology instruments. Instruments that are used must be carefully calibrated. Calibration of the spectrophotometer should be performed using an acceptable standard for hemoglobin. Calibration of the particle counter to determine RBC and WBC counts should be performed using a fresh sample of anticoagulated (EDTA) blood. PLT counting by phase hemacytometry should be used to obtain reference values for automated PLT counters. Centrifuges that are used to obtain microhematocrit values should be calibrated for maximum packing times and times checked against an electric clock. After the instruments have been calibrated, fresh whole blood is measured to determine a target value for each determination. Primary calibration of multichannel instruments is performed by calibrating each parameter to the target value. This is performed initially and then once each week. Two techniques that are commonly used to monitor instrument performance are: 1) the use of at least two levels of commercially prepared control samples to prepare either Levey-Jennings charts or the simple Cusum charts, which detect presymptomatic instrument problems; and/or 2) the use of 500-1,000 patient indices and mean WBC counts analyzed by the XB statistic to establish limits for monitoring instrument performance.

Hematology↗
PubMed2003

Separation of phytic acid and other related inositol phosphates by high-performance ion chromatography and its applications.

A high-performance anion-exchange chromatographic method was developed for the separation of phytic acid and other inositol phosphates (myo-inositol bis-, tris-, tetrakis-, and pentakisphosphates) with gradient elution and ultraviolet absorbance detection after post-column derivatization. With the acidic eluents, the combination of anion-exchange and ion suppression retention mechanisms led to the separation of 35 inositol phosphates (excluding enantiomers) into 27 peaks for the first time, and the retention behaviors of all myo-inositol bis- to hexakisphosphate isomers were studied. The whole separation procedure was completed within 65 min. Based on the investigations of nonenzymatic hydrolysis of phytic acid under different conditions by using this method, an in-house reference standard solution was produced, which can be used for method development. In addition, by applying this method to in vitro kinetic studies, at least one new enzymatic hydrolysis pathway of phytic acid was found, and one rule of enzymatic dephosphorylation of inositol phosphates (position effect) was proposed and another one (neighboring effect) was confirmed. The principle of the proposed identification approach for several inositol phosphate isomers based on hydrolysis products study will be applicable to other natural products analysis, for which standards are very expensive or not available.

Chromatography, High Pressure Liquid↗
PubMed1999

High-performance liquid chromatographic determination of n-methylformamide, a biological index for occupational exposure to dimethylformamide.

This report describes an analytical method for the biological monitoring of workers exposed to N,N-dimethylformamide (DMF), a solvent widely used in the chemical industry. The human main metabolites of DMF are N-hydroxymethyl-N-methylformamide (HMMF) and the minor metabolites N-methylformamide (NMF) and N-acetyl-S-(N-methylcarbamoyl)cysteine. The metabolite selected by the American Conference of Governmental Hygienists for occupational biomonitoring purposes, is NMF measured by gas chromatographic analysis, as during it HMMF may be converted to the minor metabolite NMF. HMMF and NFM can be measured independently using HPLC analysis. The procedure proposed here involves the thermal transformation of the primary metabolite HMMF into the minor metabolite NMF, which is then determined by HPLC. This method makes it possible to determine, using HPLC, both metabolites of DMF by measuring only one peak, thus offering two major advantages: (i) it increases the sensitivity of the test and (ii) it deploys only one reference standard.

Calibration↗
PubMed2003

A method for the absolute quantification of cDNA using real-time PCR.

Real-time PCR is an extremely powerful technique, however, often its results are open to interpretation since there is no convention for data presentation. This anomaly has arisen because many applications rely on non-standard calibration genes, which themselves often change in value during experimental manipulation. We present a novel method for absolute quantification of cDNA species using a combination of extremely accurate double-stranded DNA quantification and a plasmid reference curve. PicoGreen and reference standards are used to measure the amount of cDNA present in a sample using fluorescence. Real-time PCR products are cloned into plasmids and then used to calibrate unknown samples. This cloning is achieved using the same primers necessary for real-time PCR and thus does not involve a second design stage. Results are expressed as copy number per microgram of oligo-dT primed cDNA and consequently may be compared between both inter and intra-experimentally. We show results from a sample human system in which absolute levels of interferon-gamma, TNF-alpha, interleukin-2 and interleukin-10 are measured. We further compare the copy numbers of these genes with levels of released protein and find remarkable correlation. Although our interest has been cytokine quantification, we believe that this technique is widely applicable to the majority of real-time PCR applications.

Cytokines↗
PubMed2006

Development of a normal human immunoglobulin G standard curve for enzyme-linked immunosorbent assay: use for comparison of antigen efficacy.

Internal standard reference curves are used in enzyme-linked immunosorbent assay (ELISA) plates to control for inter- and intra-assay variance. To compare the diagnostic potential of multiple T. solium antigens on an unbiased, universal scale, we have created a standard curve using normal, human immunoglobulin G (hIgG). The hIgG curve is inexpensive and simple to prepare, and remains stable at 5 degrees C for at least one year, with a coefficient of variance of less than 10%. The hIgG standard curve has proven a critical tool for the comparison of several diagnostic antigens slated for assay development.

Animals↗
PubMed2006

Standard infrared absorption spectrum of betaine and optimal conditions for its measurement.

The infrared absorption (IR) spectrum is often used as a standard reference in identification tests of food additives in Japan. In the case of betaine, many different IR spectra have been reported and, therefore, it is necessary to establish an IR spectrum that is reproducible and reliable enough to be used as a standard for identification. In the present study, suitable conditions to obtain a standard IR spectrum were examined from various viewpoints, including pretreatment, selection of method, and measuring technique. The KBr disk method, which has generally been used to identify betaine, was found to be humidity-dependent, and there was also an interaction between betaine and KBr. A reproducible IR spectrum suitable as a standard could be obtained by drying betaine at 105 degrees C for 3 hours over phosphorus pentoxide, and then measuring the IR spectrum by the liquid paraffin (Nujol) paste method.

Betaine↗
PubMed2003

Updated gestational age specific birth weight, crown-heel length, and head circumference of Chinese newborns.

OBJECTIVE: To construct gestation specific standards of birth weight, crown-heel length, and head circumference of Chinese infants. DESIGN: A prospective cross sectional population study. METHODS: The birth weight, crown-heel length, and head circumference were prospectively measured using standard equipment in newborns delivered at 24-42 weeks gestation in the maternity units of 10 public hospitals and two private hospitals in Hong Kong. The findings were used to construct gestation specific standards of these variables. The LMS method using maximum penalised likelihood was used to perform model fitting. The results were compared with those obtained from a cohort of infants born in the same locality between 1982 and 1986. RESULTS: From October 1998 to September 2000, a total of 10 032 infants were measured, representing 9.6% of the total deliveries in Hong Kong during that period. An extra 307 infants with gestation < or = 35 weeks were recruited from October 2000 to June 2001. Each of the three variables showed a normal distribution at each gestational week. Gestation specific reference standards for each variable were constructed for male and female infants separately. Comparison with the 1982-1986 cohort showed a significant secular trend to increased birth weight. The trend was small, but significant, for crown-heel length and head circumference. CONCLUSION: These growth standards will provide useful references for the care of newborns of ethnic Chinese origin. These standards, especially that for birth weight, should be updated regularly.

Birth Weight↗