Negative Predictive Value Of Assay Research Articles

Molecular Screening of Nasopharyngeal Carcinoma: Detection of LMP-1, LMP-2 Gene Expression in Vietnamese Nasopharyngeal Swab Samples.

Objective:This study aimed to characterize the expression of LMP-1, LMP-2 in clinical swab samples in order to find out the potential molecular based biomarker for NPC diagnosis and screening, which could offer a chance in development of rapid method for NPC diagnosis in Vietnamese population. Materials and Methods:A total of 93 nasopharyngeal carcinoma swab samples and 100 healthy nasopharyngeal swab samples were collected to evaluate LMP-1, LMP-2 expression by Real-time reversed PCR. Results:we figured out the significant association between the expression of LMP-1 (counting for 48.39%), LMP-2 (counting for 39.78%) and NPC. No LMP-1 expression was observed, and only 1 of 100 specimens was detected with LMP-2 positive in healthy samples. In the combination of LMP-1 (+) and/or LMP-2 (+), the frequency of positive was 53.76%, greater than each gene expression. Additionally, sensitivity, specificity, positive predictive value, negative predictive value of assay were 99.00%, 98.04%, 69.72%, and 77.02%, respectively. Additionally, the LMP-2 expression level was 5.50 times higher in NPC samples than non-cancerous samples. Conclusion:Our results indicated the molecular invasive method based on the expression of LMP-1, LMP-2 in swab samples would be a promising supplement in NPC diagnosis, screening in the near future in Vietnam.

Evaluation of Gene Xpert Mtb/Rif Assay for the Detection of Mycobacterium Tuberculosis in Sputum of Patients Suspected of Pulmonary Tuberculosis Visiting National Tuberculosis Centre, Thimi, Bhaktapur, Nepal

Introduction: Tuberculosis (TB) is one of the most deadly and common major infectious diseases in developing countries. Rapid and accurate diagnosis of tuberculosis is indispensable to adequately manage the disease and control its transmission. The objective of this study was to evaluate Gene Xpert MTB/RIF Assay for detection of M. tuberculosis in sputum of patients suspected of pulmonary tuberculosis and its comparison with traditional conventional methods.Methodology: A total of 138 patients sputum samples were collected and processed. Gene Xpert MTB/ RIF Assay, culture method and smear microscopy were performed under standard guideline inside biosafety cabinet class II. Data were reported, structured and analyzed using SPSS version 16.00. Study was carried out from June to November 2014.Results: Assay detected M. tuberculosis in 37 (26.81%) samples out of total 138. Of these 37, 10 and 3 were resistance and indeterminate to rifampicin respectively. Culture, Ziehl-Neelsen staining and Auramine staining were positive in 43 (31.16%), 18 (13.04%) and 24 (17.39%) samples respectively. Sensitivity, specificity, Positive predictive value and Negative predictive value of Assay were 76.74%, 95.79%, 89.19% and 90.09% respectively with reference to gold standard culture method.Conclusions: Assay was found rapid in direct detec tion of Mycobacterium tuberculosis in sputum sample and was also found more sensitive than both Ziehl-Neelsen staining and Auramine staining and especially showed good promise in diagnosis of smear negative specimens.SAARC J TUBER LUNG DIS HIV/AIDS, 2016; XIII(1), page: 16-22

Computed tomographic pulmonary angiography and pulmonary embolism: predictive value of a d-dimer assay

BackgroundComputed tomographic pulmonary angiography (CTPA) is increasingly being used as first investigation for suspected pulmonary embolism (PE). The investigation has high predictive value, but is resource and time intensive and exposes patients to considerable radiation. Our aim was to assess the potential value of a negative d-dimer assay to exclude pulmonary emboli and reduce the number of performed CTPAs.MethodsAll CTPAs performed in a Scottish secondary care hospital for a fourteen month period were retrospectively reviewed. Collected data included the presence or absence of PE, d-dimer results and patient demographics. PE positive CTPAs were reviewed by a specialist panel.ResultsPulmonary embolisms were reported for 66/405 (16.3%) CTPAs and d-dimer tests were performed for 216 (53%). 186/216 (86%) patients had a positive and 30 (14%) a negative d-dimer result. The panel agreed 5/66 (7.6%) false positive examinations. The d-dimer assay's negative predictive value was 93.3% (95% CI = 76.5%-98.8%) based on the original number of positive CTPAs and 100% (95% CI = 85.9%-100%) based on expert review. Significant non-PE intrapulmonary pathology was reported for 312/405 (77.0) CTPAs, including 13 new diagnoses of carcinoma.ConclusionsWe found that a low d-dimer score excluded all pulmonary embolisms, after a further specialist panel review identified initial false positive reports. However, current evidence-based guidelines still recommend that clinicians combine a d-dimer result with a validated clinical risk score when selecting suitable patients for CTPA. This may result in better use of limited resources, prevent patients being exposed to unnecessary irradiation and prevent potential complications as a result of iodinated contrast.

Detection of methicillin-resistant Staphylococcus aureus (MRSA) from nasal samples by multiplex real-time PCR based on dual priming AT-rich primers

In this study, we reported on the design of a multiplex real-time PCR assay based on SYBR Green I, incorporating dual priming adenine-thymine (AT)-rich primers for direct detection of MRSA from nasal samples. The multiplex real-time polymerase chain reaction (RT-PCR) assay reported in this study is based on SYBR Green I with incorporation of six dual priming AT-rich primers designed from the SCCmec/orf junction. A string (4-6 bp) of low-melting bases, such as adenine and thymine, was incorporated into the primers, which virtually divided a single primer in two functional regions, thus decreasing non-specific PCR products. The analytical sensitivity and specificity of the RT-PCR assay was determined with genomic DNA of reference strains (MRSA, MSSA, and MRCoNS). RT-PCR assay was performed for analysis of 72 nasal swab specimens, and the results were confirmed by use of a culture method. Furthermore, the results of RT-PCR were compared with LightCycler MRSA advance test. The multiplex RT-PCR assay reproducibly detected a minimum of 1 pg genomic DNA (31.5 copy of genome) of MRSA reference strains and clinical isolates, with a specific melting peak at 83.5 ± 1.5°C, and neither fluorescence nor a melting peak was detected in non-target isolates. The concordance rate between RT-PCR assay and culture method was 87.5% with Cohen's kappa value (κ) 0.75, which showed good agreement between the two assays. The sensitivity, specificity, positive predictive value, and negative predictive value of the assay were 93.5%, 82.9%, 80.5%, and 94.4%, respectively. In a comparative study for the detection of 72 nasal samples, the sensitivity, specificity, positive predictive value, and negative predictive value of the multiplex RT-PCR assay with respect to LightCycler MRSA advance test was 84.2%, 88.2%, 89%, and, 83.3%, respectively. The results of RT-PCR assay demonstrated high specificity (88.2%) and positive predictive value (89%) for the direct detection of MRSA from nasal samples.

The Usefulness of Whole-blood Interferon-gamma Release Assay for the Diagnosis of Extra-pulmonary Tuberculosis

Background: The whole-blood interferon-gamma release assay (QuantiFERON-TB Gold [QFT-G]: Cellestis, Carnegie, Victoria, Australia) has been studied primarily for the use of diagnosing active pulmonary tuberculosis (TB) or latent TB. In the present study, the usefulness of QFT-G was evaluated for the diagnosis of extra-pulmonary tuberculosis (EP-TB). Methods: From June 2006 to February 2009, we evaluated the usefulness of QFT-G in patients (n=65) suspected with EP-TB, retrospectively. The diagnostic sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the QFT-G assay were analyzed. Results: EP-TB was diagnosed in 33 (51%) participants. The overall sensitivity, specificity, PPV, and NPV of the QFT-G assay for EP-TB were 78%, 79%, 81%, and 77%, respectively. Of the 33 with EP-TB, 14 (42%) were diagnosed with TB pleurisy, 7 (21%) with TB lymphadenitis, 7 (21%) with intestinal TB, and 5 (15%) with EP-TB in other sites. In subgroup analyses according by site of infection, the QFT-G showed 86% sensitivity, 64% specificity, and 78% NPV in TB pleurisy. On the other hand, the sensitivity, specificity, and NPV of the assay were 71%, 83% and 71%, respectively in TB lymphadenitis, and 86%, 100% and 88%, respectively in intestinal TB. Among the patients with suspected alternative site EP-TB, the sensitivity, specificity, and NPV of the assay were 50%, 80% and 67%, respectively. Conclusion: The QFT-G assay showed moderate diagnostic accuracy in EP-TB. However, negative QFT-G assay does not exclude EP-TB because of the low NPV of this assay.

Does a negative D-dimer exclude thrombosis?

The marked sensitivity of assays of cross-linked fibrin degradation products (XL-FDP) or D-dimer tests for the detection of physiologic fibrinolytic activity has been exploited to exclude the presence of an active thrombotic disorder. For example, as reviewed by Devine in this symposium, a lack of elevation of the concentration of XL-FDP has a negative predictive value of greater than 90% in patients with suspected deep venous thrombosis. Similarly, Deitcher and Eisenberg recently reported that a normal concentration of XL-FDP essentially excluded the presence of gram-negative bacteremia in patients with suspected sepsis.’ The negative predictive value of assays of XL-FDP in plasma from patients with these clinical conditions is dependent on the extent to which increases in intravascular fibrinolytic activity are reflected by increases in the concentration of XL-FDP. While assays of XL-FDP appear to be sensitive and specific for characterizing the intensity of physiologic fibrinolytic activity, it is important to recognize that differences in the immunogenicity of specific XL-FDP, as well as varying intensities of physiologic fibrinolytic response among individuals, may influence the extent to which a low or normal concentration of XL-FDP can be interpreted as excluding thrombosis or increased fibrinolysis.