Early detection; can not do harm; better to know; negative test indicates disease absence; early treatment is more effective; helps prevention.
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Prior Probability
P(disease)= prevalence in population
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Post-test Probability
P(disease)= very much higher or very much lower
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Incidence
The number of new cases presenting in a given time
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Prevalence
The number of cases present in the defined population at any point in time.
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Sensitivity
Proportion of diseased group that have abnormal results
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Specificity
Proportion of normal group tests that have normal results.
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P(belief correct| new evidence)
P(belief correct) x LR
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Likelihood Ratio (LR)
P (Evidence|assuming belief correct) / P (Evidence|assuming belief incorrect) = sensitivity / (1-specificity)
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P (disease| pos)
(P(disease) x P(pos 1 disease)) / (P(disease) x P(pos 1 disease) + P(no disease) x P(pos 1 no disease)
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Colorectal Cancer Screening - Faecal Occult Blood Test
Prevalence = 0.3%. Sensitivity= 50%. Specificity= 97%. Before screening Prevalence=0.3%
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Disease NHS Criteria
Important health problem, numbers affected seriousness
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Test NHS Criteria
Simple, safe, precise and validated- lab evidence.
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Treatment NHS Criteria
Effective treatment with evidence that early treatment leads to better outcomes. Repeat screening if disease onset insidious
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Ethical Implications of Genetic Testing
Direct-to-consumers, duty to disclose, genetic discrimination, reproductive issues, societal values, test utility.
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The Screening Program
Benefits must outweigh physical and psychological harm. Delivered in units large enough for monitoring and audit
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Phenylketinurine (PKU)
Inborn error of metabolism, decreased metabolism of the amino acid Phenylketinurine. leads to intellectual disabilities, musty smell and lighter skin. simple treatment of reduced Phe in diet.
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Congenital Hypothyroid
Disorder affecting the thyroidgland, in the neck. Doesn't produce thyroxine -hypothroidism. Neonatal screening, blood spot TSH, can cause brain damage (cretinism)
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Neural tube defects - aFP
Downs syndrome or cystic fibrosis. Curable by gene therapy or I intra-uterine surgery.
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Colorectal Cancer
Investigating tets acceptability, 90% will not have cancer. Current test is guaiac qualitative FOB pos/neg
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Prostate Cancer
Risk management programme. Raised PSA from Ca prostate, benign prostatic hypertrophy, prostatitis. Follow up test invasive, not risk free. Treatment not proven to decrease mortality.
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Cystic Fibrosis
1:25 population is a carrier, occurs in 1:2500 caucasian births. Aggressive treatment marked prolongs disease free life.
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Cystic Fibrosis Treatment
Ante-natal genetic screening of mother then father. Neo-Natal immuno-reacrive trypsinogen. Also screen for MCCAD & sickle cell thalassaemaia.
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Other cards in this set
Card 2
Front
P(disease)= prevalence in population
Back
Prior Probability
Card 3
Front
P(disease)= very much higher or very much lower
Back
Card 4
Front
The number of new cases presenting in a given time
Back
Card 5
Front
The number of cases present in the defined population at any point in time.
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