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PubMed1998

[Measurement of regional cerebral blood flow using one-point arterial blood sampling and microsphere model with 123I-IMP: correction of one-point arterial sampling count by whole brain count ratio].

A correction method was proposed for measurement of the regional cerebral blood flow using one-point arterial blood sampling and a microsphere model with N-isopropyl-p-(123I)iodoamphetamine (123I-IMP). Instead of using continuous arterial blood sampling octanol-extracted counts, one-point arterial sampling whole blood counts corrected by the whole brain count ratio using 1-minute planar SPECT images were employed. The experimental subjects were 189 patients with cerebrovascular disorders. 123I-IMP, 222 MBq, was administered by intravenous infusion. Continuous arterial blood sampling was carried out for 5 minutes, and arterial blood was also sampled once at 5 minutes after 123I-IMP administration. Then the whole blood count of the one-point arterial sampling was compared with the octanol-extracted count of the continuous arterial sampling. A positive correlation was found between the two values (r = 0.87, p < 0.001). The correction method was carried out by calculation as follows. The ratio of the continuous sampling octanol-extracted count (OC) to the one-point sampling whole blood count (TC5) was compared with the whole brain count ratio (5:29 ratio, Cn) using 1-minute planar SPECT images, centering on 5 and 29 minutes after 123I-IMP administration. Correlation was found between the two values (r = 0.72, p < 0.001). The following relationship was shown from the correlation equation. OC/TC5 = 0.390969 x Cn-0.08924. Based on this correlation equation, we calculated the theoretical continuous arterial sampling octanol-extracted count (COC). COC = TC5 x (0.390969 x Cn-0.08924). There was good correlation between the value calculated with this equation and the actually measured value (r = 0.94, p < 0.001). The coefficient improved to r = 0.94 from the r = 0.87 obtained before using the 5:29 ratio for correction. For 23 of these 189 cases, another one-point arterial sampling was carried out at 6, 7, 8, 9 and 10 minutes after the administration of 123I-IMP. The correlation coefficient was also improved for these other point samplings when this correction method using the 5:29 ratio was applied. It was concluded that it is possible to obtain highly accurate input functions, i.e., calculated continuous arterial sampling octanol-extracted counts, using one-point arterial sampling whole blood counts by performing correction using the 5:29 ratio.

Blood↗
PubMed2000

Differences between Internet samples and conventional samples of men who have sex with men: implications for research and HIV interventions.

The Internet is becoming a new erotic oasis for obtaining sex online or in person. We reviewed the literature on cybersex and compared differences in data from samples of homosexually active men obtained on identical questionnaires from a conventional written questionnaire, distributed through the mailing and contact lists of a large national gay organization in Sweden, and through the same organization's website and chat room. A total of 716 written questionnaires and 678 Internet questionnaires were obtained. The Internet sample was younger, more likely to live in small towns or cities, live with parents or a girlfriend, and have lower formal education. They are less likely to have previous sexual experience solely with other men (one in three of the Internet sample vs. 1 in 14 of the written sample defined themselves as bisexual) and more likely to visit erotic oases such as bathhouses, video clubs and erotic movie houses. They also visited Internet chat rooms more frequently (86% of the Internet sample vs. 50% of the written sample). One third of the Internet sample wanted the opportunity to talk with an expert about HIV compared with a quarter of the written sample. Sexual practices between the two samples were generally similar, although the Internet sample reported significantly less body contact, kissing, hugging, mutual masturbation, and more condom use for anal intercourse with steady partners. Over four times as many of the Internet samples reported sex with women in the past year as the written sample. These data indicate that Internet data collection is feasible and that this mode of data collection, despite the nonrandom and self-selected nature of both types of samples, is likely to be more significantly oriented toward the young, geographically more isolated, and more behaviorally and self-identified bisexual respondent than conventionally distributed written questionnaires.

Adult↗
PubMed2006

Sequential sampling protocols for Spodoptera frugiperda (Lepidoptera: Noctuidae), on Zea mays fields: influence of sampling unit size.

Spodoptera frugiperda (J.E. Smith) is a major pest in maize fields in Argentina. However, a sampling method that accounts for spatial pattern and allows reliable pest density estimations is still lacking. This paper addresses the issue of how sampling unit size can influence the characterization of S. frugiperda spatial pattern and the performance of sampling plans. An intensive sampling programme for S. frugiperda larvae was carried out in maize fields from October until March in four growing seasons. On each sampling date, 12 to 20 sampling units were taken at random. Each unit consisted of 1, 2, 4, 6, 8, 10 or 12 consecutive plants along a row. The linearized version of the Taylor's power law (TPL) was fitted to mean and variance estimated for each sampling date and data set through least squares regression. In general, b values from TPL were significantly >1 (P<0.05), indicating an aggregated sampling distribution. Regression slopes (b) ranged from 1.28 to 1.48 in small larvae and from 1.06 to 1.24 in large larvae, indicating stronger clumping in the former. TPL parameters were used to develop constant precision sampling plans. The efficiency of these plans in terms of expected total cost (searching and handling sampling units) was very sensitive to the size of the sampling units with small larvae but not with large larvae. The influence of sampling unit size and spatial pattern on TPL parameters and sampling costs is discussed.

Animals↗
PubMed2006

Fluorescence imaging of sample zone narrowing and dispersion in a glass microchip: the effects of organic solvent (acetonitrile)-salt mixtures in the sample matrix and surfactant micelles in the running buffer.

A mismatch in the EOF velocities between the sample zone and running buffer region is known to generate pressure-driven, parabolic flow profile of the sample plug in electrokinetic separation systems. In the present study, video fluorescence microscopy was employed to capture real-time dynamics of the sample plug (containing fluorescein as the probe molecule) in a discontinuous conductivity system within a glass microchip, in which the sample matrix consisted of a mixture of ACN and salt (NaCl), and the running buffer contained sodium cholate (SC) micelles as the pseudo-stationary phase (i.e., performing "ACN stacking" in the mode of MEKC). Upon application of the separation voltage, the video images revealed that zone narrowing and broadening of the probe molecules occurred as the sample plug headed toward the cathode during the initial time period, probably resulting in part from the stacking/sweeping, and destacking of the SC micelles at the boundaries between the sample zone and running buffer. Interestingly, a second sample zone narrowing event can be observed as the sample plug moved further toward the cathode, which could be attributed to the sweeping of the slower moving probe molecules by the faster moving SC micelles that originated from the anode. This phenomenon was studied as a function of pH, sample plug length, as well as the concentration of organic solvent and salt in the sample matrix. The data suggested that the presence of large amounts of an organic solvent (such as ACN or methanol) and salts in the sample matrix not only induces sample dispersion due to the formation of a pressure-driven (hydrodynamic) flow, but may also lead to the formation of a double sample zone narrowing phenomenon by altering the local EOF dynamics within the separation system.

Acetonitriles↗
PubMed1995

222Rn in water: a study of two sample collection methods, effects of mailing samples, and temporal variation of concentrations in North Carolina groundwater.

The U.S. Environmental Protection Agency has proposed a drinking water standard for 222Rn in public water supplies. When promulgated, operators of public water supplies will be required to determine water 222Rn concentrations. Most likely, water samples will be collected and mailed to laboratories for analyses. Additionally, it is probable that homeowners will test private well water in a similar manner by collecting water samples and mailing them to a laboratory for 222Rn analyses. In anticipation of these actions, this study was conducted to evaluate two methods of water sample collection and to evaluate the potential losses of 222Rn from water samples mailed to a laboratory. Thirdly, temporal variations in 222Rn concentrations in several groundwater supplies in North Carolina were examined. Water supplies at four sites in eastern North Carolina and five sites in western North Carolina were sampled over a 7-mo period beginning in the fall of 1993 and continuing through the spring of 1994. Samples were analyzed using a liquid scintillation method. This study showed that a "slow-flow" method is not only suitable for sample collection, but may be the preferable method for water sample collection since slow-flow collection resulted in less 222Rn loss than was observed during syringe collection, i.e., the water 222Rn concentrations in samples collected by the slow-flow method were generally higher. Further, based on this study, mailing water samples to a laboratory for analysis should not have a substantial effect on the measured 222Rn concentrations. Consequently, water samples can be collected by the slow-flow method by water supply operators, as well as homeowners, and mailed to laboratories for 222Rn analyses with reasonable assurance that the samples have not suffered significant 222Rn loss. Temporal variations in water 222Rn concentrations were observed in this study. One factor complicating the study of temporal variations in 222Rn concentrations was the striking influence that inconstant water usage and inadequate well purging prior to sample collection had on 222Rn loss from the water.

Evaluation Studies as Topic↗
PubMed2007

Checking the consistency of the two blood samples slope-intercept method for estimating GFR using the single blood sample formula in children.

BACKGROUND: The slope-intercept method is widely used for the determination of the plasma clearance of 51Cr-EDTA. When three or more plasma samples are used, the goodness-of-fit (r2) can be used as a measure of consistency of the samples. This parameter can not be used, however, if only two samples are available. PURPOSE: To evaluate whether the single-sample technique (SBS) can be used to check the consistency of the slope-intercept method using two blood samples (2BS) in children. METHODS: Simulated computer models of a mono-exponential curve were created in order to represent three children aged 3, 6 and 10 years, each with a large range of clearances values and three distribution volumes, respectively 20%, 25% and 30% of body weight. Errors were then introduced in the injected dose (errors from -50% to +50%) and on the 120 or 240 min blood sample (errors from -50% to +50%). The effects of these errors on the clearance measurement using 2BS and SBS methods were calculated and compared. RESULTS: The errors on the injected dose, the 120 min and 240 min plasma samples introduced errors in the same direction and with the same magnitude on both the SBS and 2BS clearance values. For that reason, the comparison between the SBS methods and the 2BS techniques has a low sensitivity in detecting an eventual error. Striking differences between the SBS method and the 2BS technique were only observed when considerable errors on the injected dose or plasma samples were introduced, particularly in case of a reduced clearance. The comparison between the SBS clearances calculated using the 120 min sample to that obtained using the 240 min samples is slightly more sensitive. However, this approach is also slightly less specific. A difference of more than 10 ml . min(-1). 1.73 m(-2) can be observed in the absence of an error. CONCLUSIONS: The use of the SBS for checking the consistency of the 2BS constitutes an insensitive approach to detect an eventual error in the injected dose or in the plasma samples. Obvious different results obtained by SBS and 2BS or between the SBS calculated using the 120 min and the 240 min samples suggest the presence of an error, but comparable results do not exclude erroneous measurement. Moreover, a difference of more than 10 ml . min(-1). 1.73 m(-2) can be observed in the absence of an error in the injected dose or in the plasma samples.

Body Size↗
PubMed1998

Control by sample location in pigeons' matching to sample.

Three experiments assessed the impact of sample location in pigeons' matching to sample. Experiments 1 and 2 demonstrated that after line or hue identity matching was acquired to high levels of accuracy with center-key samples, varying sample location across the three keys disrupted performances. The drop in accuracy occurred following both zero-delay and simultaneous training and was mostly confined to trials in which the sample appeared on a side key. Experiment 3 attempted to diminish control by location by training birds to match samples that could appear in any location prior to center-key sample training and moving-sample testing with another set of stimuli. In testing, all birds performed accurately on center-sample trials and on side-key sample trials in which the matching choice appeared on the center key. Accuracy was below chance, however, on side-key sample trials in which the matching choice appeared on the other side key. One implication of the persistent control by sample location in the three-key paradigm is that it precludes the possibility of symmetry because symmetry tests require a change in the locations at which samples and comparisons appear.

Animals↗
PubMed1999

Base rates versus sample accuracy: competition for control in human matching to sample.

People often place undue weight on specific sources of information (case cues) and insufficient weight on more global sources (base rates) even when the latter are highly predictive, a phenomenon termed base-rate neglect. This phenomenon was first demonstrated with paper-and-pencil tasks, and also occurs in a matching-to-sample procedure in which subjects directly experience case sample (cue) accuracy and base rates, and in which discrete, nonverbal choices are made. In two nonverbal experiments, subjects were exposed to hundreds of trials in which they chose between two response options that were both probabilistically reinforced. In Experiment 1, following one of two possible samples (the unpredictive sample), either response was reinforced with a .5 probability. The other sample (predictive) provided reinforcement for matching on 80% of the trials in one condition but in only 20% of the trials in another condition. Subjects' choices following the unpredictive sample were determined primarily by the contingencies in effect for the predictive sample: If matching was reinforced following the predictive sample, subjects tended to match the unpredictive sample as well; if countermatching the predictive sample was generally reinforced, subjects tended to countermatch the unpredictive sample. These results demonstrate only weak control by base rates. In Experiment 2, base rates and sample accuracy were simultaneously varied in opposite directions to keep one set of conditional probabilities constant. Subjects' choices were determined primarily by the overall accuracy of the sample, again demonstrating only weak control by base rates. The same pattern of choice occurred whether this pattern increased or decreased rate of reinforcement. Together, the results of the two experiments provide a clear empirical demonstration of base-rate neglect.

Adult↗
PubMedDate not supplied

Sampling and sample preparation for detection and quantitation of natural toxicants in food and feed.

The primary goal of a sampling plan for natural toxins, i.e., mycotoxins and seafood toxins, is to obtain a sample that accurately represents the concentrations of individual components of a given lot. Factors affecting the ability of the sampling plan to accomplish this goal include: (1) nature of the analyte of interest; (2) distribution of the analyte throughout the lot, (3) physical characteristics of the product, (4) accessibility of the product to random representative sampling, (5) sampling procedure, and (6) size of sample. Sampling plans are composed of 3 distinct components: (a) sampling, (b) sample preparation, and (c) analysis. Normally, sampling contributes the largest relative error while analysis comprises the least. Automatic, continuous stream samplers provide the most representative samples for commodities such as nuts, cottonseed, and cereal grains. Good sample preparation equipment is currently available for these commodities; the use of this equipment to obtain a representative test sample is discussed.

Animal Feed↗
PubMed2000

Instruments for transcervical chorionic villus sampling for prenatal diagnosis.

BACKGROUND: The type of instrument used in chorion villus sampling could have a significant impact on the success rate of the procedure. An ability to manoeuvre the instrument within the uterine cavity without puncturing the gestational sac, and to see the tip of the instrument on ultrasound scanning are particularly important. OBJECTIVES: The objective of this review was to assess the effects of different instruments for transcervical chorionic villus sampling on perinatal outcome, quality and quantity of obtained tissue, technical difficulties during the procedure and maternal adverse effects. SEARCH STRATEGY: The Cochrane Pregnancy and Childbirth Group trials register was searched. Date of last search: October 1998. SELECTION CRITERIA: Randomised trials comparing different instruments for transcervical chorionic villus sampling. DATA COLLECTION AND ANALYSIS: Eligibility and trial quality were assessed by one reviewer. MAIN RESULTS: Three trials involving 268 women were included. None of the trials mentioned method of randomisation. An adequate sample was more likely to be obtained using small forceps than aspiration cannula (odds ratio 7.29, 95% confidence interval 3. 39 to 15.67). However small forceps were more difficult to insert than an aspiration cannula (odds ratio 0.35, 95% confidence interval 0.13 to 0.96). Use of the Portex cannula was more likely to result in an inadequate sample and a difficult or painful procedure when compared with either the silver or aluminium cannula respectively. REVIEWER'S CONCLUSIONS: Although there is some evidence to support the use of small forceps for transcervical chorionic villus sampling, it is not strong enough to support change in practice for clinicians who have become familiar with aspiration cannulas.

Chorionic Villi Sampling↗
PubMed2004

Internal jugular vein sampling in adrenocorticotropic hormone-dependent Cushing's syndrome: a comparison with inferior petrosal sinus sampling.

OBJECTIVE: Distinguishing between pituitary-dependent Cushing's syndrome (CS) and occult ectopic ACTH syndrome can be extremely difficult. Bilateral inferior petrosal sinus sampling has been shown to have the highest diagnostic accuracy in this subtype evaluation. Internal jugular vein sampling (IJVS) has been reported as a potentially safer invasive alternative, but data are limited. Our objective was to compare the sensitivity and specificity of bilateral IJVS and bilateral inferior petrosal sinus sampling (IPSS) in patients with ACTH-dependent CS. DESIGN: We prospectively collected blood samples from the inferior petrosal sinus and internal jugular vein of consecutive patients with ACTH-dependent CS. PATIENTS: The study group included 35 patients: 32 with pituitary-dependent CS (positive immunohistochemical findings for ACTH pituitary tumour or biochemical cure after pituitary surgery) and three with histologically proven ectopic ACTH syndrome. MEASUREMENTS: Inferior petrosal sinus sampling and bilateral IJVS were performed simultaneously before and after administration of corticotropin-releasing hormone (CRH), and ratios of central-to-peripheral ACTH concentrations were calculated. RESULTS: The basal IJVS central-to-peripheral ACTH ratios were diagnostic for pituitary-dependent CS (> 2) in 15 patients (46.9%), as were basal inferior petrosal sinus sampling central-to-peripheral ACTH ratios in 29 patients (90.6%). The post-CRH IJVS central-to-peripheral ACTH ratios were diagnostic for pituitary-dependent disease (> 3) in 24 patients (75%), as were post-CRH inferior petrosal sinus sampling central-to-peripheral ACTH ratios in 28 patients (87.5%). In the three patients with ectopic ACTH CS, the IJVS and inferior petrosal sinus sampling pre- and post-CRH ACTH ratios were correctly negative. The overall sensitivity of combined pre- or post-CRH was 81.3% for IJVS and 93.8% for inferior petrosal sinus sampling. Because of the difference between mean ratios in the two techniques, new criteria for IJVS were mathematically calculated: a pre-CRH central-to-peripheral ACTH ratio of 1.59 and a post-CRH central-to-peripheral ACTH ratio of 2.47 maximized sensitivity and specificity when both of these are equally taken into consideration. CONCLUSION: In conclusion, IJVS is not superior to inferior petrosal sinus sampling for establishing the cause of ACTH-dependent CS. When new criteria of basal (> 1.6) and post-CRH (> 2.5) central-to-peripheral ACTH gradients were applied to ACTH ratios from IJVS, the sensitivity of this test was maximized. However, confirmatory inferior petrosal sinus sampling is recommended when there is a lack of a central-to-peripheral ACTH gradient and when there is only a gradient above the cut-off on basal (pre-CRH) sampling.

ACTH Syndrome, Ectopic↗
PubMed1978

Sampling of speech pathology treatment activities: an evaluation of momentary and interval sampling procedures.

Videotaped samples of aphasia treatment sessions were coded, using the Clinical Interaction Analysis System (CIAS), a 39-category system for recording the events that occur in clinician-patient interactions during aphasia treatment sessions. These coded records were then sampled according to various schedules and procedures and the fidelity with which each sampling schedule and procedure represented the content of the entire treatment record was evaluated. In addition, trained observers coded videotaped samples of treatment, using the CIAS with a number of sampling schedules and procedures. The fidelity with which these observers' records represented the content of the treatment sessions sampled was then evaluated. The results of the analysis indicated that momentary sampling at intervals distributed throughout the session generates more accurate records of session content than single longer samples taken from the session, unless those single samples comprise a major part of the session, and that sampling representativeness remains high even when only one event in ten is sampled, if sampled events are uniformly distributed throughout the session.

Aphasia↗
PubMed1983

Control of pigeons' matching-to-sample performance by differential sample response requirements.

Pigeons were trained on a matching-to-sample task in which sample hue and required sample-specific observing behavior provided redundant, relevant cues for correct choices. On trials that involved red and yellow hues as comparison stimuli, a fixed-ratio 16 schedule (FR 16) was required to illuminate the comparisons when the sample was red, and a differential-reinforcement-of-low-rates 3-sec schedule (DRL 3-sec) was required when the sample was yellow. On trials involving blue and green hues as comparison stimuli, an FR 16 schedule was required when the sample was blue and a DRL 3-sec schedule was required when the sample was green. For some pigeons, a 0-sec delay intervened between sample offset and comparison onset, whereas other pigeons experienced a random mixture of 0-sec and 2-sec delay trials. Test trial performance at 0-sec delay indicated that sample-specific behavior controlled choice performance considerably more than sample hue did. Test performance was independent of whether original training involved all 0-sec delay trials or a mixture of 0-sec and 2-sec delays. Sample-specific observing response requirements appear to facilitate pigeons' matching-to-sample performance by strengthening associations between the observing response and correct choice.

Animals↗
PubMed2003

A method to combine non-probability sample data with probability sample data in estimating spatial means of environmental variables.

In estimating spatial means of environmental variables of a region from data collected by convenience or purposive sampling, validity of the results can be ensured by collecting additional data through probability sampling. The precision of the pi estimator that uses the probability sample can be increased by interpolating the values at the nonprobability sample points to the probability sample points, and using these interpolated values as an auxiliary variable in the difference or regression estimator. These estimators are (approximately) unbiased, even when the nonprobability sample is severely biased such as in preferential samples. The gain in precision compared to the pi estimator in combination with Simple Random Sampling is controlled by the correlation between the target variable and interpolated variable. This correlation is determined by the size (density) and spatial coverage of the nonprobability sample, and the spatial continuity of the target variable. In a case study the average ratio of the variances of the simple regression estimator and pi estimator was 0.68 for preferential samples of size 150 with moderate spatial clustering, and 0.80 for preferential samples of similar size with strong spatial clustering. In the latter case the simple regression estimator was substantially more precise than the simple difference estimator.

Data Collection↗
PubMed2005

A field study to assess the long-term sampling feasibility of evacuated canisters and the development of a mathematical model to analyze potential sampling bias.

Small, evacuated canisters (300 mL) equipped with a unique capillary flow controller were used to evaluate airborne concentrations of Stoddard solvent. The physical characteristics of the flow controller permitted the collection of air samples for a time period of 40 hours (5 consecutive work days). Long-term sampling (greater than 8 hours) is rarely performed in industrial hygiene due to limitations in current air sampling technology but may provide valuable information in characterizing worker cumulative exposures for some processes. A field study was performed to evaluate the feasibility of collecting a 40-hour area sample using the small canisters. Six canister samplers were used as area monitors to evaluate a cleaning operation for an entire workweek. For comparison, 30 diffusive badges (6 per day) were simultaneously used to monitor the same process. No statistical difference was found between the time-weighted average for the two sampling methods (p > 0.05). In addition, the canister samples integrate airborne concentrations for an entire workweek and therefore peak concentrations are not explicitly observed. Thus, an examination of peak exposures using simulated concentrations was conducted. A mathematical model was developed to determine whether a significant sampling bias was associated with long-term canister sampling when peak concentrations are present. The maximum possible bias was determined to be less than 9% for peak amplitudes having 10 times the background concentration and well below that for smaller amplitudes. Long-term sampling with the small, evacuated canisters was found to provide results comparable to sorbent sampling methods but with the added benefit of a significantly increased sampling time.

Adult↗
PubMed2007

Variation of estimates of SNP and haplotype diversity and linkage disequilibrium in samples from the same population due to experimental and evolutionary sample size.

Studies of genetic polymorphisms and diversity between and within human populations are increasingly characterised by a very large number of genetic markers but using a relatively small number of individuals from which DNA samples were taken. In this report we examine the limitations of a small experimental sample size relative to a large genomic sample size, and quantify the sampling variance of a number of measures of diversity and linkage disequilibrium. The relationship between sample size and observed levels of polymorphism and haplotype diversity at the level of a gene is investigated under a neutral model of sequence evolution, using coalescent simulations. It is shown that the effect of evolutionary sampling, as manifested by differences between samples (genes) in measures of diversity estimated using very large sample sizes, is substantial, with a coefficient of variation of the number of detected polymorphic SNPs or haplotypes in the order of 15%. The effect of experimental design (sample size) is also very large, and a number of 'significant' results reported in the literature can be explained by sampling alone. The expected correlation coefficient of measures of linkage disequilibrium across samples from the same population has been quantified and found to be consistent with empirical estimates from the literature.

Chromosomes, Human↗
PubMedDate not supplied

Sampling, sample preparation, and analytical variability associated with testing wheat for deoxynivalenol.

The variability associated with testing wheat for deoxynivalenol (DON) was measured using a 0.454 kg sample, Romer mill, 25 g comminuted subsample, and the Romer Fluoroquant analytical method. The total variability was partitioned into sampling, sample preparation, and analytical variability components. Each variance component was a function of the DON concentration and equations were developed to predict each variance component using regression techniques. The effect of sample size, subsample size, and number of aliquots on reducing the variability of the DON test procedure was also determined. For the test procedure, the coefficient of variation (CV) associated with testing wheat at 5 ppm was 13.4%. The CVs associated with sampling, sample preparation, and analysis were 6.3, 10.0, and 6.3%, respectively. For the sample variation, a 0.454 kg sample was used; for the sample preparation variation, a Romer mill and a 25 g subsample were used; for the analytical variation, the Romer Fluoroquant method was used. The CVs associated with testing wheat are relatively small compared to the CV associated with testing other commodities for other mycotoxins, such as aflatoxin in peanuts. Even when the small sample size of 0.454 kg was used, the sampling variation was not the largest source of error as found in other mycotoxin test procedures.

Algorithms↗
PubMed2005

Pitfalls of immunoassay and sample for IGF-I: comparison of different assay methodologies using various fresh and stored serum samples.

OBJECTIVE: Determination of insulin-like growth factor (IGF)-I is now a routine adjunct to multiple research and clinical investigations. Evidence has associated higher IGF-I levels with various human pathologies, but the reported associations have not been invariably confirmed. We examined the potential for post-sampling proteolysis and evaluated the impact of such events on IGF-I immunoassays. DESIGN AND METHODS: We compared IGF-I in different sets of fresh and frozen old samples using four different and commonly used immunoassays. The potential for post-sampling proteolysis was further examined by assaying fresh samples stored for 4 weeks at various temperatures in the absence or presence of protease inhibitors. RESULTS: IGF-I levels in fresh serum samples from adult males, females, and pregnant subjects by all methods were similar and were highly correlated (r=0.85-0.97). The same was true for levels in frozen ( approximately 2 years at --80 degrees C) samples from diabetic patients, which are reportedly associated with enhanced proteolytic activity. In contrast, in another set of frozen adult male and female samples ( approximately 8 years at --20 degrees C), the inter-method median IGF-I levels varied by approximately 3- to 4-fold and the values poorly correlated. Similar variability in the inter-method response was also observed when IGF-I in the replicates of fresh samples stored at 4 degrees C for 4 weeks was measured. However, the 4 degrees C storage effect could be completely blocked by the addition of protease inhibitors, allowing for all assays to detect 92--101% of the expected mean levels. CONCLUSIONS: The data indicate susceptibility of IGF-I to significant post-sampling proteolysis and suggest the importance of immunoassays for the intact molecule. Immunoassays that lack specificity for intact IGF-I may mask the potential pathophysiological effects of proteolysis and generate misleading results, particularly in studies involving inappropriately stored and/or proteolyzed samples. In such cases, underestimation of the in vivo levels by the intact assays would occur, but the findings of low IGF-I levels may be indicative of questionable sample quality.

Adult↗