3h03 lecture 3 - Enzyme-linked immunosorbent assay Specimen...

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Enzyme-linked immunosorbent assay Microtiter well E E E E E Specimen 2nd antibody E Substrate S P
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HAMA “bridging” interference E E E E 2nd antibody E Substrate S P
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HAMA blocking interference E E E E
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Distinguishing between Health and Disease: The role of the clinical laboratory in the diagnostic process Clinical Biochemistry 3H3
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What is normal??? • Normal Health – choice between defining an ‘ideal state’ or determining an ‘average’ state in people considered healthy – more practical to analyze ‘average’ state --with respect to a biological parameter results in a symmetric (Gaussian) distribution
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The Disease State • A population having a specific disease will usually have an asymmetric (nonparametric) distribution .
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Diagnostic process involves gathering information until, ideally, the probability of the disease approaches 100%. in practice, this value is much lower at the time of the decision.
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Defining the value of a Diagnostic Test The clinical performance of a laboratory test defines how well it predicts disease The sensitivity of a test indicates the likelihood that it will be positive when disease is present The specificity of a test indicates the likelihood that it will be negative when disease is absent Distinction between a test being a true positive ( TP ) or true negative ( TN ) is usually determined with reference to a selected “normal range” based on 95% confidence. This range is referred to as a Reference Range (RR) . Test focuses on the upper or lower limit often use a Reference Value (RV) . False Positive (FP) Normal people falling outside RR False Negative (FN) Diseased individual falling inside RR
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Defining the value of a Diagnostic Test
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Defining the value of a Diagnostic Test Reference state (RS): conditions in which the RR is assumed to apply – “Ideal world” RS would include sex, ethnicity, weight range, diet In practice RR are applied to a much larger population • distinction made between neonate, pediatric, obstetrics and geriatric practices Establishing a Reference Range – min 100 subjects – Test should be validated under the following conditions: • in healthy subjects • in patients with the disease – no symptoms –fu l l symp tom s • subjects who not have the disease but whose signs and symptoms mimic the disease • subjects having a pathologic conditions associated with the same organ system
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Laboratory Test Characteristics •Sensitivity(SENS)- the test “positivity” SENS= TP X 100 TP +FN =% of disease cases that give a positive result with the RV selected •Specificity(SPEC)- the test “negativity” SPEC= TN X 100 TN +FP =% of non-disease cases that give a negative result with the RV selected
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Example Example Of 25 admitted cocaine abusers, 23 tested positive for urinary benzoylecgonine and 2 tested negative. What is the sensitivity of the urine screen?
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3h03 lecture 3 - Enzyme-linked immunosorbent assay Specimen...

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