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1、資料的評讀(II) 診斷與篩檢,神經內科 王志弘,診斷的過程,Initiation of diagnosis hypothesis 初步診斷 我想這病人可能有 。 Refinement of the diagnostic causes 修正診斷 他可能不是X 或 Y ，但到底是何種感染呢？ Narrowing the possibilities Defining the final diagnosis 最終診斷 我們應該再做個XX 切片確定，再來治療,初步診斷,目前有上萬種的診斷疾病 如果我們不認識這個疾病，我們就不可能考慮到這個診斷 關於疾病發生比例的文獻，讓我們了解各種診斷的可能性（pre
2、test probability）,修正診斷,根據 Symptoms, 症狀 Signs, 徵象 Laboratory tests, 實驗室檢查 Imaging, 影像檢查,診斷性試驗的實證,Evidence about “diagnostic tests” Is this evidence about the accuracy of diagnostic test valid? Is this (valid) evidence show that the test is useful at all? How can I apply this valid, accurate diagnosti
3、c test to a specific patient?,文獻評讀,治療性 Validity (closeness to the truth) Impact (size of the effect) Applicability (usefulness in our clinical practice),診斷性 Is this evidence about the accuracy of diagnostic test valid? Is this (valid) evidence show that the test is useful at all? How can I apply thi
4、s valid, accurate diagnostic test to a specific patient?,Valid Useful Apply,什麼是正常,BNP vs LV dysfunction,Is this evidence about the accuracy of a diagnostic test valid?,Validity about Diagnostic Tests,Diagnostic Test in Question Reference (gold) standard,常見的 GOLD STANDARDS,外科或是病理標本 血液培養的菌株 風溼熱， Jones
5、 Criteria DSM IV (精神疾病) X 光 長期追蹤,代表性,該檢查是否在適當的病患族群中被評估過（尤其是那些在臨床上會使用此一檢查的對象） Representative common presentation of the target disorder confusing presentations include patients, with mild and severe, early and late, treated and untreated cases.,確定性,無論檢查結果如何，參考標準（reference standard）是否經過確認 如何達到確定診斷? 另一
6、個參考標準 長期追蹤 確定不會延誤治療,測量,Independent and blind measurement Psychiatric disorders,Is this (valid) evidence show that the test is useful at all?,Sensitivity, Specificity, Likelihood ratios,整體盛行率,Prevalence = ( a + c) / ( a + b + c +d ) = 809 / 2579 = 31% Pre-test probability,Positive predictive value,陽性
7、預測值= a / (a + b) = 731 / 1001 = 73% 檢查陽性（ferritin 65）的人當中，真正有病（缺鐵性貧血）的人的比例,Negative predictive value,陰性預測值= d / (c + d) = 1500 / 1578 = 95% 檢查陰性（ferritin 65）的人當中，真正沒有病（缺鐵性貧血）的人的比例,Positive vs Negative Predictive Value,Pre-test probability: 測前機率 Post-test probability: 測後機率 根據前兩張slide： Positive predic
8、tive value: 73% Negative predictive value: 95% 假設抽血檢查前病人(有病)的測前機率：50% 如果陽性反應 測後機率：73% 如果陰性反應 測後機率： 1-95% = 5%,Sensitivity,敏感度= a / (a + c) = 731 / 809 = 90% 真正有病的人當中，檢查有問題（陽性）的比例,Specificity,特異度= d / (b + d) = 1500 / 1700 = 85% 真正沒病的人當中，檢查沒問題（陰性）的比例,Likelihood Ratio,可能性比率 陽性結果的可能性比率 LR+ = (出現目標疾病的病人
9、中，檢查結果為陽性的可能性） / (沒有出現目標疾病的病人中，檢查結果為陽性的可能性） = 敏感度 / (1- 特異度) = 90% / (1-85%) = 6,Likelihood Ratio,陰性結果的可能性比率 LR- = (出現目標疾病的病人中，檢查結果為陰性的可能性） / (沒有出現目標疾病的病人中，檢查結果為陰性的可能性） = (1-敏感度) / 特異度 = (1-90%) / 85% = 0.12,勝算 vs 機率,Odds vs Probability 假設有病與沒病的機率分別是 31%，69% 則有病的勝算為：31%/69% = 0.45 Study pre-test odd
10、s = prevalence / (1-prevalence),Post-test Odds 測後勝算,LR+ = (出現目標疾病的病人中，檢查結果為陽性的可能性） / (沒有出現目標疾病的病人中，檢查結果為陽性的可能性） LR+(ferritin)= sensitivity/(1-specificity) = 90%/15%=6 測後勝算(陽性反應) = 測前勝算 * LR+ =1 * 6 = 6 測後勝算(陰性反應) = 測前勝算 * LR-,Post-test Odds vs Probability,測後機率 = 測後勝算 / (測後勝算+1) Study pre-test odds =
11、 0.45 Study post-test odds = 0.45 *6 = 2.7 Study post-test probability = 2.7 /(2.7+1) = 73%,Post-test Odds , Probability (陰性),測後機率 = 測後勝算 / (測後勝算+1) Study pre-test odds = 0.45 Study post-test odds = 0.45 *0.12 = 0.054 Study post-test probability(有病) = 0.054/(0.054+1) = 5% 測後沒病機率 = 1-5% = 95% negativ
12、e predictive value,個人化調整,病患測後勝算 = 研究測後勝算 * (病患測前勝算/研究測前勝算),檢查是否有用,Sensitivity 敏感度, Specificity 特異度 兩者相加減掉100% (Youden Index) 至少要大於 0, 最好要大於 50%, 理想值是 100%,Rule in / Rule out,SnNout: high sensitivity, negative result rule out the diagnosis SpPin: high specificity, positive result rule in the diagnosi
13、s LR+ = sensitivity / (1-specificity) LR- = (1-sensitivity) /specificity,D-dimer vs Deep Vein Thrombosis Sensitivity: 97.7% Specificity: 46%,Ferritin vs Iron deficiency anemia Sensitivity: 90%, specificity: 85%,How can I apply this valid, accurate diagnostic test to a specific patient?,Is the diagno
14、stic tests,Available Affordable Accurate Precise In our setting,Patients Pre-Test Probability,From personal experience, prevalence statistics, practice database, primary studies The study patients similar to our own ? If the disease probability changes after the evidence,Results Affect our managemen
15、t?,Move us across a test-treatment threshold Our patient willing to carry it out The consequence of the test help the patient reach his/her goal,Multilevel likelihood ratios,Multiple Tests,Prediction rule,SCREENING,Screening Early diagnosis of pre-symptomatic disease among well individual in public,
16、Case-finding Early diagnosis of pre-symptomatic disease among patients who came to us for other unrelated diseases,Harm of Early Diagnosis,Label: high risk for developing some disease False positive screening test Early diagnosis may not make people live longer, but it surely makes all of them “sick” longer.,Screening 有效嗎?,通常願意來接受篩檢的人，對醫囑的遵從性較高 自然預後較好 早期診斷通常會找到進展較慢的疾病,Diagnostic test,診斷不是用來發現絕對的事實 是用來減少臨床診斷的不確定性,