Occurrence Of False-positive Results Research Articles

Clinical Strategies in Gene Screening Counseling for the Healthy General Population.

The burgeoning interest in precision medicine has propelled an increase in the use of genome tests for screening purposes within the healthy population. Gene screening tests aim to pre-emptively identify those individuals who may be genetically predisposed to certain diseases. However, as genetic screening becomes more commonplace, it is essential to acknowledge the unique challenges it poses. A prevalent issue in this regard is the occurrence of falsepositive results, which can lead to unnecessary additional tests or treatments, and psychological distress. Additionally, the interpretation of genomic variants is based on current research evidence, and can accordingly change as new research findings emerge, potentially altering the clinical significance of these variants. Conversely, a further prominent concern regards false assurances in genetic testing, as genetic tests can yield false-negative results, potentially posing a significant clinical risk. Moreover, the results obtained for the same disease can vary among different genetic testing services, due to differences in the types of variants assessed, the scope of tests, analytical methods, and the algorithms used for predicting diseases. Consequently, whereas genetic testing holds significant promise for the future of medicine, it poses unique challenges. If conducted without a full understanding of its implications, genetic testing may fail to achieve its purpose potentially hindering effective health management. Therefore, to ensure a comprehensive understanding of the implications of genetic testing within the general population, sufficient discussion and careful consideration should be given to counseling based on gene test results.

Establishment and application of a screening method for α-glucosidase inhibitors based on dual sensing and affinity chromatography

α-Glucosidase plays a direct role in the metabolic pathways of starch and glycogen, any dysfunction in its activity could result in metabolic disease. Concurrently, this enzyme serves as a target for diverse drugs and inhibitors, contributing to the regulation of glucose metabolism in the human body. Here, an integrated analytical method was established to screen inhibitors of α-glucosidase. This step-by-step screening model was accomplished through the biosensing and affinity chromatography techniques. The newly proposed sensing program had a good linear relationship within the enzyme activity range of 0.25 U mL−1 to 1.25 U mL−1, which can quickly identify active ingredients in complex samples. Then the potential active ingredients can be captured, separated, and identified by an affinity chromatography model. The combination of the two parts was achieved by an immobilized enzyme technology and a microdevice for reaction, and the combination not only ensured efficiency and accuracy for inhibitor screening but also eliminated the occurrence of false positive results in the past. The emodin, with a notable inhibitory effect on α-glucosidase, was successfully screened from five traditional Chinese medicines using this method. The molecular docking results also demonstrated that emodin was well embedded into the active pocket of α-glucosidase. In summary, the strategy provided an efficient method for developing new enzyme inhibitors from natural products.

Diatoms pass through the gastrointestinal barrier and lead to false-positive: an animal experiment.

The diatom test has been used by forensic pathologist as standard for drowning, but the occurrence of false-positive results (presence of diatoms found in the tissues of subjects who died from causes other than drowning) draws criticism regarding the specificity of the test. Diatoms within food or water can be ingested through the gastrointestinal tract. However, the mechanisms of how the diatoms reach distant organs such as the lung, liver, and kidney have not been studied. In this article, we simulated the process of diatoms entering the gastrointestinal tract using gastric lavage on experimental rabbits. Diatoms are detected in lymph from a lymphatic vessel at the root of the mesentery, portal vein blood, aortic blood, lung, liver, and kidney samples in the gavage group. Of diatoms, 76.24% were the centric diatom, 99.86% of diatoms have a maximum size of less than 50µm, and most of diatoms concentrate in the lung. Our study provided the evidence supporting the theory that the diatoms could pass through the gastrointestinal barrier and reach the rabbits' other internal organs. The diatoms could reach internal organs through the portal vein and lymphatic vessel at the root of the mesentery. This provides us new insight into our understanding of false-positive diatom test in forensic pathology.

Evaluation of the initial specimen diversion technique (ISDT) for reducing blood culture contamination in children: a prospective randomized controlled trial

Blood cultures are one of the important tools for laboratory diagnosis of bloodstream infection [1]. One of the main limitations of blood cultures is the occurrence of false-positive results caused by skin contaminants. False-positive results can impact on patient care, e.g., improper antibiotic treatment, additional investigations for possible infection, increased length of stay and higher costs [2,3]. Rates of blood culture contamination in children vary between centres but are typically not less than 3% [4].

Qualitative and semi-quantitative screening of selected psychoactive drugs in blood: Usefulness of liquid chromatography – triple quadrupole and quadrupole time-of-flight mass spectrometry in routine toxicological analyses

Routine toxicological analysis requires broad screening for a large number of therapeutically prescribed and other compounds, and/or their metabolites. This article specifically focuses on three classes of psychoactive substances: antidepressants (ADs), antipsychotics (APs) and benzodiazepines and Z-drugs (BZDs). Two screening methods were compared for their ease-of-use in a routine setting, based upon the analysis of 105 medico-legal case samples. Analytes of interest were extracted using liquid–liquid extraction and separated using liquid chromatography with a total run time of 12 min per sample. A first detection method used targeted triple quadrupole mass spectrometry, operated in triggered multiple reaction monitoring mode (tMRM). False negative results were noted for 15% of the total number of detected analytes only, the majority of which were either present at sub- to low therapeutic levels or were metabolites of other analytes in the samples. The occurrence of false positive results was rare. A second screening method used quadrupole time-of-flight mass spectrometry (QTOF) for untargeted data acquisition. Data analysis was facilitated by the creation of an in-house, subset mass spectral database. As was seen for the tMRM screening, false negative results were observed in less than 20% of the total number of detected analytes, either for compounds at low concentrations or of which metabolites could be identified in the samples. More false positive results were observed due to an observed bias for prothipendyl. Determination of the exact concentration in a sample may only be required depending on the specific case circumstances. For this purpose, semi-quantification using each of the screening methods was investigated. Excellent results were observed using the tMRM method in combination with a small number of labelled internal standards (n = 12). Semi-quantification using the QTOF screening method was more laborious, but limited results on selected compounds indicated equally good results. Overall, the developed semi-quantitative screening methods performed well and – following further validation on case samples – could be implemented for most compounds in routine toxicological analysis without the need for highly trained or specialised personnel.

The Role of Molecular Imaging in a Muscle-Invasive Bladder Cancer Patient: A Narrative Review in the Era of Multimodality Treatment.

Diagnostic imaging in bladder cancer plays an important role since it is needed from pretreatment staging to follow-up, but a morphological evaluation performed with both CT and MRI showed low sensitivities and specificities in detecting pathologic lymph nodes, due to the occurrence of false positive results. Implementation of functional information provided by PET/CT could be a determinant in the management of patients with muscle-invasive bladder cancer. A focus on the role of 18F-FDG PET/CT and alternative tracers in patients with muscle-invasive bladder cancer is provided in this analysis in order to outline its potential applications in staging settings and response evaluation after neoadjuvant chemotherapy.

Thousands of Alpha Tests

Abstract Data snooping is a major concern in empirical asset pricing. We develop a new framework to rigorously perform multiple hypothesis testing in linear asset pricing models, while limiting the occurrence of false positive results typically associated with data snooping. By exploiting a variety of machine learning techniques, our multiple-testing procedure is robust to omitted factors and missing data. We also prove its asymptotic validity when the number of tests is large relative to the sample size, as in many finance applications. To improve the finite sample performance, we also provide a wild-bootstrap procedure for inference and prove its validity in this setting. Finally, we illustrate the empirical relevance in the context of hedge fund performance evaluation.

Evaluation of immunoglobulin M-specific capture enzyme-linked immunosorbent assays and commercial tests for flaviviruses diagnosis by a National Reference Laboratory

Zika and Dengue viruses present considerable immunological cross-reactivity, resulting in a troublesome serodiagnosis due to occurrence of false positive results. Due to Brazil’s wide variety of circulating flaviviruses we aimed to access the use of in house serological tests adapted by National Reference Laboratory for Arboviruses in Brazil and evaluate commercial tests available. We evaluated in house IgM ELISAs for the individual detection of anti-ZIKV, -DENV, and –YFV IgM, against a panel of samples positive for dengue, zika, yellow fever, Rocio, Ilheus, Saint Louis encephalitis, West Nile and chikungunya. We also evaluated two commercial kits for dengue and zika IgM detection recommended by the Brazilian Ministry of Health in 2015. The sensitivity and specificity for the in house ZIKV IgM ELISA was 60.0 % and 88.6 % and for the in house DENV IgM ELISA was 100 % and 82.2 %, respectively. The in house YFV IgM ELISA presented 100 % for both sensitivity and specificity. The Novagnost Zika Virus IgM test presented a sensitivity of 47.3 % and specificity of 85.3 % and the Serion ELISA classic Dengue Virus IgM, 92.8 % and 58.9 %, respectively. Overall, both in house ELISAs for ZIKV and DENV adapted and evaluated here, presented better performances than the commercial kits tested.

EXPERIENCE OF NON-INVASIVE PRENATAL TEST (NIPT) AT FERNANDEZ HOSPITAL.

AIM: Non -Invasive Prenatal Test is the testing for cell free fetal DNA from maternal blood during pregnancy for Trisomy 21, 18,13 and Monosomy 45XO. The aim of our study is to review our institution’s experience in the use of non-invasive prenatal test for aneuploidy screening METHODS: It is a retrospective study of pregnant women who had undergone non-invasive prenatal test between January 2015 and December 2018 at Fernandez Hospital. A detailed Ultrasonogram is done as a mandatory prerequisite before NIPT to rule out major structural anomalies; pre and post- test counselling was done to all pregnant women who underwent non-invasive prenatal test RESULTS: 322 women who had undergone non-invasive prenatal test were included in the study. 32% of the study population were of advanced maternal age. Low fetal fraction was seen in 2.1% of the study population. An abnormal non -invasive prenatal result (aneuploidy detected or inconclusive result) was reported in 36/322(11%).NIPT had a sensitivity of 100% and specificity of 99.6% in our study. Ever since NIPT has been introduced in our clinical practice the rate of invasive tests performed declined and the number of non-invasive prenatal test performed increased yearly CONCLUSION: NIPT is an excellent method for screening for aneuploidy. There is an increasing uptake of NIPT and a decline in the rate of invasive tests performed. The occurrence of false positive results emphasizes that NIPT is a screening test and not to be considered as a replacement for diagnostic tests.

Thousands of Alpha Tests

Data snooping is a major concern in empirical asset pricing. We develop a new framework to rigorously perform multiple hypothesis testing in linear asset pricing models, while limiting the occurrence of false positive results typically associated with data snooping. By exploiting a variety of machine learning techniques, our multiple-testing procedure is robust to omitted factors and missing data. We also prove its asymptotic validity when the number of tests is large relative to the sample size, as in many finance applications. To improve the finite sample performance, we also provide a wild-bootstrap procedure for inference and prove its validity in this setting. Finally, we illustrate the empirical relevance in the context of hedge fund performance evaluation.

The scenario tree epidemiological model in estimation effects of B. melitensis Rev 1 vaccination on disease prevalence

minant brucellosis. The stochastic scenario tree model was used to simulate vaccination and surveillance implementation during 8 years. Outputs were annual proportions of true positive, true negative, false positive, and false negative flocks. Vaccination coverage was described by the Pert distribution with average 70% and min and max 50% and 80%, respectively. Effects of risk factors (high prevalence-areas and transhumance) were considered. The model was separately simulated for three levels of initial average flock prevalence (2%, 5%, and 10%). In the following years, flock prevalence arising from the fitted distribution of the false negative flocks from the previous year increased by the estimated reproductive number. Average within flock prevalence was provided separately for the vaccinated and unvaccinated flocks, indirectly accounting for the vaccine efficacy. Specificity of the diagnostic tests (Rose Bengal plate and Complement fixation) was reduced by 5% for the vaccinated flocks to represent the increased occurrence of false positive results. Each simulation was iterated 1000 times using @Risk, providing average prediction and 5th and 95th percentile of outputs. According to our estimates, only consistent vaccination combined with systematic removal of diseased animals can result in significant reduction of disease prevalence.

Molecular insights into brown rust resistance and potential epidemic based on the Bru1 gene in sugarcane varieties and new elite clones

In most sugarcane cultivation areas, sugarcane brown rust (SBR), caused by Puccinia melanocephala, is an economically important fungal disease that leads to severe yield loss in susceptible cultivars. Bru1, which is the major dominant SBR resistance gene, has been widely used in the prediction of brown rust resistance in sugarcane. In this study, three panels of sugarcane germplasms, the major varieties approved over the past 10 years and new elite clones in the current national regional trial, together with one panel of Saccharum spontaneum, were employed in estimating the possibility of SBR epidemic and to assess the efficiency of 9O20-F4-HaeIII in eliminating false positives. Among the current top five varieties used as sucrose feedstock, accounting for more than 68.9% of the total cultivated area, all were highly resistant to SBR, although only three harboring Bru1. Two major varieties Yuetang60 and Guitang46 without harboring Bru1 were highly susceptible to SBR, together with highly susceptible Funong41, which need prudent promotion. Approximately 60.5% of the 38 new elite clones were Bru1 positive. Considering the susceptibility of Liucheng03-1137, which exhibits a strong promotion momentum, together with Funong41, Guitang46, Yuetang60, and Yunzhe06-47, four were favored by the enterprise due to their superior sucrose content and good stalk yield, despite their high susceptibility to SBR, and additional Yuetang93-159, one current top five varieties with declining resistance, which results in a potential risk for brown rust epidemic. Furthermore, low frequency of the wild germplasm of S. spontaneum from five different countries was Bru1 positive. In addition, a perfect molecular diagnostic result was observed in all modern sugarcane clones using two dominant markers, and HaeIII can prevent the occurrence of false positive results when the 9O20-F4 PCR products of S. spontaneum are digested by RsaI. The prevalent chewing cane Badila without Bru1 is highly resistant to SBR. Our results provide valuable information for the extension of sugarcane varieties and a batch of novel SBR resistance sources with superior comprehensive characters for crossbreeding, and for SBR-resistant gene pyramiding by crossing or through mining and using of new SBR-resistant genes.

Circulating Aspergillus fumigatus DNA Is Quantitatively Correlated to Galactomannan in Serum.

The performance of antigen galactomannan (GM) for diagnosing invasive aspergillosis (IA) is hampered by the occurrence of false-positive results. Quantitative PCR has been proposed to improve the diagnosis of IA. Therefore, we analyzed the value of performing a PCR test to the GM-positive serum sample. Using a quantitative PCR assay specific for Aspergillus fumigatus 28S ribosomal DNA, we retrospectively tested 422 GM-positive (Platelia Bio-Rad kit) serum samples collected over 1 year from 147 patients. The cases were classified based on EORTC criteria as “proven,” “probable,” and “no–IA” before availability of the PCR results. After exclusion of 65 samples for non-reproducibility of GM positivity (n = 62) or PCR inhibition (n = 3), 75 (21.0%) of the remaining 357 samples were PCR-positive. GM and fungal DNA showed a significantly positive correlation (p < 0.0001, R2 = 0.27, slope = 0.98 ± 0.19). At least one PCR-positive result was observed in 63.3% (31/49) of IA patients and in 13.2% (13/98) of non-IA patients (p < 0.0001). The PCR positivity was also associated with the presence of other microbiological criteria among the 44 patients with IA and complete mycological workup (p = 0.014), as well as a higher mortality rate at six months among the 135 patients with hematological conditions (p = 0.0198). Overall, we found a quantitative correlation between serum GM and circulating DNA with an increased likelihood of IA when both were positive. A PCR-positive result also supported a higher fungal load when GM was already positive. We advocate adding a PCR test for every confirmed GM-positive serum sample.

Detection of Occult Invasion in Melanoma In Situ

It is unclear why some patients with in situ melanoma develop metastases. Few reports demonstrate occult invasion with immunohistochemistry staining, which were discordant with reports interpreting such staining as false-positive. To investigate the occurrence of occult invasive disease within in situ melanoma by using methods to circumvent potential limitations in prior study designs. Unequivocal in situ melanoma without associated nevi or regression was identified using a consecutive sample of 33 cases plus 1 index case in an academic medical center. After cutting deeper into the most representative tissue block, 3 sequential slides were stained with hematoxylin-eosin (H-E), melanoma antigen (melan-A), and again with H-E. Melan-A-stained slides showing definitive invasion were double-stained with Sry-related HMg-Box gene 10 (SOX10) to confirm the melanocytic nature of the cells of interest. The study evaluated the possibilities of occult invasion detected by immunohistochemistry, sectioning deeper into the tissue block, or both. Slides were independently scored by 3 dermatopathologists with interrater reliability assessed. The study was conducted from January 1, 2012, to July 31, 2014. Assessment of the occurrence of occult invasion, diagnosis of invasion by immunohistochemistry alone vs cutting deeper into the tissue block, and occurrence of false-positive results using immunohistochemistry alone. Occult invasive melanoma was detected in 11 of 33 consecutive cases (33%) of previously diagnosed unequivocal in situ melanoma. Six of 11 melanomas (55%) were diagnosable only by immunohistochemistry. The remaining 5 tumors (45%) were diagnosable by both melan-A and H-E staining, likely as a result of simply cutting deeper into the tissue block. Four cases (12%) showed a few melan-A-positive cells in the dermis, which was insufficient for a diagnosis of invasive melanoma and most consistent on a cytomorphologic basis with occult nevi. Although rare, in situ melanoma may metastasize. Occult microinvasion was demonstrated in up to one-third of the specimens in the present study, which provides a plausible explanation for this adverse event. Thus, history and physical examination including regional lymph nodes, education, and surveillance recommendations should be based on a very low, but not zero, risk of metastasis.

An Assessment of Microbiological Methods to Test Sterility of Foot-and-mouth Disease Vaccines Produced in Brazil

Background: Foot-and-mouth vaccines are an important tool in the control and eradication of the disease. In order to be commercialized, vaccines produced in Brazil undergo an evaluation process by health authorities, which includes sterility testing, residual active virus, potency, thermal stability, volume and non-structural protein activity. Sterility tests described in the Brazilian Pharmacopeia and by the World Organization for Animal Health (OIE) include direct inoculation and membrane filtration methods. The objective of the present study was to evaluate these two methods used to analyze sterility of vaccines against foot-and-mouth disease produced in Brazil.Materials, Methods &amp; Results: Vaccines produced by the six main laboratories in Brazil were initially tested for filtration capacity. The sensitivity of the two techniques was determined artificially contaminating vaccines using known bacterial concentrations. Vaccines (9 bottles) from the same manufacturer were inoculated with 5 mL of steady-state growths of Pseudomonas aeruginosa, Candida albicans, and Clostridium sporogenes to final concentrations of 0.1, 1 and 10 CFU/ mL and a final volume of 55 mL. Bottles were manually shaken for 1 min to complete homogenization of contents. Then, 10 mL of each flask were used in assessment of the direct inoculation method, and 10 mL were used to evaluate the membrane filtration technique. Direct inoculation was carried out inoculating 1 mL of the experimentally contaminated vaccine in five tryptic soy broth (TSB) and fluid thioglycollate medium (FTM) bottles. The membrane filtration technique was carried out filtrating 10 mL of the challenged vaccines in a peristaltic pump system (SteritestTM Pump System), where vaccines were initially solubilized in Triton X-100 to promote filtration. Next, membranes are incubated in TSB and FTM. These use two types of culture medium, tryptic soy broth (TSB) and fluid thioglycollate medium (FTM), with incubation times of 20-25ºC and 30-35ºC, respectively, to detect fungi, yeasts, and aerobic and anaerobic bacteria. The medium is incubated for 14 days, to enable the detection of slow-growth microorganisms that may be in a latent stage or weakened due to the extreme conditions of the production process (like the use of cleaning and disinfection agents, ultraviolet light, and preservers, for instance). All vaccines were effectively filtered in the SteritestTM Pump System. Membrane filtration and direct inoculation presented the same sensitivity to detect yeasts (0.1 CFU/mL) and anaerobic organisms (1 CFU/mL). For the detection of aerobic organisms, membrane filtration was 100 times more sensitive, compared to direct inoculation.Discussion: The specialized literature also reports that, apart from the higher sensitivity, membrane filtration affords to reduce contamination during the procedures, since it is carried out in a closed system. In addition, it is indicated in the analysis of large sample volumes. Moreover, membrane filtration reduces the occurrence of false positive results, since it removes the excess vaccine volume from the culture medium, which may be mistaken for turbidity caused by bacterial growth. In this sense, the membrane filtration technique is more appropriate in the control of vaccine sterility in foot-andmouth disease prevention strategies, and is an interesting tool to improve quality control of the product.

The balance sheet of benefits and harms of breast cancer population-based screening in Europe: outcome research, practice and future challenges.

Breast cancer screening programs are still object of harsh debate. In 2012, the Independent UK Panel reviewed the benefits and harms of mammography screening based on randomized trials and the EUROSCREEN Working Group reviewed European observational outcome studies. The conclusion was that screening programs should continue, while acknowledging that harms, such as the occurrence of false-positive results and overdiagnosis, can have a negative impact on a woman's life. Information on the balance sheet of the benefits and harms of breast cancer screening should help women and their physicians to make an informed choice. The future challenge for breast screening programs is to assess the feasibility, acceptability, effectiveness and impact of risk-based screening in order to maximize benefit-to-harm ratios.

A three-year follow-up of congenital adrenal hyperplasia newborn screening

Objectivecongenital adrenal hyperplasia (CAH) newborn screening can prevent neonatal mortality in children with the salt-wasting form of the disease and prevent incorrect gender assignments, which can occur in females. However, the occurrence of false-positive results in preterm or low-birth-weight newborns creates some diagnostic difficulties, with consequent therapeutic implications. This study aimed to report the results of a pilot project for neonatal CAH screening conducted in the state of Minas Gerais, Brazil from 09/2007 to 05/2008 with a three-year follow-up. Methodsdried blood specimens were collected on filter paper cards three to seven days after birth of all newborns in the period. Samples were analyzed for 17-hydroxyprogesterone using an enzyme-linked immunosorbent assay (ELISA). Resultsa total of 159,415 children were screened. The apparent incidence of the classic variant of the disease was 1:9,963, based on initial diagnoses following newborn screening. During the follow-up period, eight of 16 children initially diagnosed with CAH were reclassified as unaffected, resulting in a revised incidence of 1:19,927. The false-positive rate was 0.31%, and the positive predictive value was 2.1%. Sensitivity and specificity were 100% and 99.7%, respectively. Conclusionsnewborn screening is an important public health policy in developing countries such as Brazil, where CAH remains underdiagnosed. It has great potential to identify children with the disease who otherwise cannot be diagnosed earlier. Long-term follow-up and monitoring of all children with positive screening results are crucial to ensure a correct diagnosis and to calculate a reliable incidence ratio of the disease.

A three-year follow-up of congenital adrenal hyperplasia newborn screening

Objectivecongenital adrenal hyperplasia (CAH) newborn screening can prevent neonatal mortality in children with the salt-wasting form of the disease and prevent incorrect gender assignments, which can occur in females. However, the occurrence of false-positive results in preterm or low-birth-weight newborns creates some diagnostic difficulties, with consequent therapeutic implications. This study aimed to report the results of a pilot project for neonatal CAH screening conducted in the state of Minas Gerais, Brazil from 09/2007 to 05/2008 with a three-year follow-up. Methodsdried blood specimens were collected on filter paper cards three to seven days after birth of all newborns in the period. Samples were analyzed for 17-hydroxyprogesterone using an enzyme-linked immunosorbent assay (ELISA). Resultsa total of 159,415 children were screened. The apparent incidence of the classic variant of the disease was 1:9,963, based on initial diagnoses following newborn screening. During the follow-up period, eight of 16 children initially diagnosed with CAH were reclassified as unaffected, resulting in a revised incidence of 1:19,927. The false-positive rate was 0.31%, and the positive predictive value was 2.1%. Sensitivity and specificity were 100% and 99.7%, respectively. Conclusionsnewborn screening is an important public health policy in developing countries such as Brazil, where CAH remains underdiagnosed. It has great potential to identify children with the disease who otherwise cannot be diagnosed earlier. Long-term follow-up and monitoring of all children with positive screening results are crucial to ensure a correct diagnosis and to calculate a reliable incidence ratio of the disease.

Study on the stability of internal quality control sera for HIV/AIDS immunodiagnostic tests

Introduction: The use of reference materials in order to assure and perform the quality control of analytical measurements is a requirement in clinical laboratories. Objectives: Stability of serum samples, kept frozen at -20°C for long-term storage and at varied temperatures during short periods, was evaluated by investigating the persistency of anti-human immunodeficiency virus (HIV) antibodies reactivity on enzyme-linked immunosorbent assay/enzyme immunoassay (ELISA/EIA), Western blot and indirect immunofluorescence assays. Method: The analyzed sera were part of serum panels (comprised of anti-HIV positive and negative samples), produced at the Immunology Center of Instituto Adolfo Lutz, which have been the reference specimens for producing the internal quality assurance sera of HIV/acquired immunodeficiency syndrome (AIDS) immunodiagnostic assays. Sera stability was assessed in samples stored at -20°C for 56 weeks, and at various temperature conditions: from 2°C to 8°C (refrigerator), from 15°C to 25°C (room temperature), at 37°C (incubator) and at -80°C (freezer) for 24 and 48 hours. The statistical analyses on HIV-negative serum samples (long-term storage) were significant (p < 0.05), and neither adverse effects on these samples as the occurrence of false-positive results nor false-negative results in HIV antibody positive sera were found in both studies. Conclusion: It was possible to conclude that the reference material remained stable for 48 hours at different temperatures (short-term) and it remained stable at -20°C for 56 weeks (long-term).

Testing the specificity of the diatom test: search for false-positives

The diatom test is widely used by forensic pathologists as proof of drowning, notwithstanding some criticisms mainly concerning the occurrence of false-positive results (presence of diatoms in the tissues of subjects who died from causes other than drowning). The aim of the present study was to verify the claimed inaccuracy of the method caused by an excessive rate of false-positives related to inadvertent exposure to diatoms of the general population. The study was carried out to investigate the presence of diatoms in the tissues (lungs and sternum) of subjects who died from causes other than drowning. Two groups of cadavers that underwent an autopsy at the Institute of Forensic Medicine of the University of Verona were included in the study. Group A comprised 45 individuals who died from causes other than drowning, whereas Group B comprised 20 bodies which had been recovered from water. The extraction of the diatoms was performed by incubation of samples in nitric acid for 48 hours at 60°C. The analysis of the samples from Group A showed the absence of diatoms in both lung and sternum samples. In Group B all lung samples showed the presence of diatoms, whereas only six sternum samples were shown to contain diatoms. The difference between Groups A and B was statistically highly significant. The absence of diatoms in the samples collected from Group A falsified the hypothesis that false-positive results from the diatom test may occur due to diatoms entering living bodies through the respiratory and/or digestive tracts via air, water or food, supporting the validity of the diatom test as proof of drowning.