Assessment of RNA splicing (including splicing errors).Assessment of gene expression by measuring mRNA levels (e.g., expression of the FMR1 gene in different tissues in fragile X syndrome ).In case of chemiluminescent DNA/ RNA, a CCD camera that captures a digital image is used.This film develops when exposed to the label, creating dark regions that correspond to the target protein band. When radiolabeled detector DNA/ RNA is used, an x-ray film is placed against the western blot.One labeled strand that can be visualized using one of the following techniques:.One unlabeled strand (cleaved RNA sample ).Labeled p robes recognize and anneal to the complementary strand if it is present on the membrane.The membrane is incubated with labeled probes of RNA or DNA.Separated and cleaved RNA is transferred (blotted) to a membrane.The RNA sample is cleaved by enzymes and separated by gel electrophoresis (commonly on agarose gels). DNA or RNA labeled with a chemiluminescent dye.Principle of detection: annealing of marked detector RNA or DNA to the target RNA fragment.Results from laboratory studies should always be interpreted in conjunction with the medical history, clinical examination, and other diagnostic tests. Medical interpretation based on the combination of test results, patient history, and physical examination findings.Ensuring the correct allocation of results to patient data.The most important steps of the postanalytical phase include: Microscopy: e.g., manual blood cell count with differential.Photometry: e.g., indirect determination of glucose concentration.Immunochemistry: e.g., ELISA for the detection of PSA.Quantitative methods: The concentration of a substance is determined.Qualitative methods: The result is either positive or negative.The analytical phase comprises sample processing and the generation of results. Preanalytical-phase errors (i.e., errors during sample collection or transport) should be considered if actual test results differ significantly from expected results. Shaking of blood samples, leading to hemolysis.Exposure to strong light (e.g., leading to degradation of bilirubin, resulting in falsely low levels).Errors during sample transport, such as:.Errors during sample collection (e.g., prolonged venous stasis during blood collection, which can lead to falsely elevated levels of potassium and calcium ).Interference factors: affect sample quality.Fluid collection from punctures (e.g., ascites, pleural effusion).Cerebrospinal fluid (see “ Cerebrospinal fluid analysis”).Urine (see “ Diagnostic evaluation of the kidney and urinary tract”).See also “ Evaluation of diagnostic tests” in “ Epidemiology.” Specificity and sensitivity are important factors that should be considered when selecting a diagnostic test (e.g., many screening tests have a high sensitivity but low specificity). The preanalytical phase encompasses the selection of relevant diagnostic tests and the collection and transport of samples.
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