Bài giảng y học chứng cứ bài 5 chứng cứ của các nghiên cứu chuẩn đoán, trình bày cơ sở chuẩn đoán, đánh giá các nghiên cứu chuẩn đoán, sai lầm trong chuẩn đoán, thiết kế cơ bản của một nghiên cứu chuẩn đoán chính xác

Bài 5: CHỨNG CỨ CỦA CÁC NGHIÊN CỨU CHẨN ĐOÁN Matthew J Thompson p GP & Senior Clinical Scientist Department of Primary Health Care University of Oxford Nội ộ dung g học ọ „ „ Cơ sở chẩn đoán Đánh giá nghiên cứu chẩn đoán Chẩn đoán gì? „ „ „ „ „ „ Làm tăng độ ắ chắn ắ việc mắc hay không mắc bệnh Tính trầm trọng bệnh Giám sát theo dỏi diển biến lâm sàng Đánh g giá tiên lượng-nguy ợ g g y cơ/ giai đoạn bệnh Kế hoạch điều trị Kịp lúc Knottnerus, BMJ 2002 Sai lầm chẩn đoán „ Hầu hết sai lầm chẩn đoán cognitive errors: „ „ „ Conditions of uncertainty Thinking is pressured Shortcuts are used (Ann Croskerry Croskerry Ann Emerg Med 2003) „ Những sai lầm chẩn đoán (Diagnostic errors The next frontier for Patient Safety Newman-Toker, JAMA 2009) „ „ 40,000-80,000 40 000 80 000 US h hospital it l d deaths th ffrom misdiagnosis per year Adverse events, negligence cases, serious disability more likely to be related to misdiagnosis than drug errors Diagnostic reasoning „ Diagnostic strategies particularly important where patients present with variety of conditions and p possible diagnoses g Diagnostic reasoning „ „ Thí dụ: nguyên nhân ho gì? Comprehensive history examination diagnosis final diagnosis differential Diagnostic reasoning „ „ For example, what causes cough? Comprehensi e history…examination…differential Comprehensive histor e amination differential diagnosis…final diagnosis „ Cardiac failure failure, left sided , Chronic obstructive pulmonary disease , Lung abscess Pulmonary alveolar proteinosis, Wegener's granulomatosis, Bronchiectasis Pneumonia, Atypical pneumonia, Pulmonary hypertension Measles, Oropharyngeal cancer, Goodpasture's syndrome Pulmonary oedema, Pulmonary embolism, Mycobacterium tuberculosis Foreign body in respiratory tract, Diffuse panbronchiolitis, Bronchogenic carcinoma Broncholithiasis, Pulmonary fibrosis, Pneumocystis carinii Captopril, Whooping cough, Fasciola hepatica Gastroesophageal reflux, Schistosoma haematobium, Visceral leishmaniasis Enalapril, Pharyngeal pouch, Suppurative otitis media Upper respiratory tract infection, Arnold's nerve cough syndrome, Allergic bronchopulmonary aspergillosis Chlorine gas, Amyloidosis, Cyclophosphamide Tropical pulmonary eosinophilia, Simple pulmonary eosinophilia, Sulphur dioxide Tracheolaryngobronchitis Extrinsic allergic alveolitis Tracheolaryngobronchitis, alveolitis, Laryngitis Fibrosing alveolitis, cryptogenic, Toluene di-isocyanate, Coal worker's pneumoconiosis Lisinopril, Functional disorders, Nitrogen dioxide, Fentanyl Asthma, Omapatrilat, Sinusitis Gabapentin, Cilazapril „ ……diagnostic di ti reasoning i „ „ „ „ „ „ „ „ „ „ „ „ „ „ „ „ „ Đánh g giá test chẩn đoán Kết có giá trị? Kết quảả gì? ì? Kết có giúp chăm sóc ó bệnh ệ nhân â không? Thiết kế nghiên cứu chẩn đốn xác Hàng loạt bệnh nhân Chỉ số test Tham chiếu tiêu chuẩn vàng ( gold”) standard Xếp loại bệnh nhân (Blinded cross classification) cross l ifi ti ) Validity y of diagnostic g studies Was an appropriate pp p spectrum p of p patients included? Were all patients subjected to the gold standard? Was there an independent, blind or objective comparison p with the g gold standard? x table: negative predictive value + Disease - + a b - c d Test NPV = d / c + d Proportion of people with a negative test who not have the disease Wh t’ wrong with What’s ith PPV and d NPV? „ Depend on accuracy of the test and prevalence of the disease p Likelihood ratios „ „ Can use in situations with more than test outcomes Direct link from pre-test probabilities to post-test post test probabilities x table: positive likelihood ratio + + a Disease - How much more often a positive test occurs in people with compared to those without the disease b LR+ = a/a+c / c / b/b+d b/b d Test - c d or LR+ = sens/(1 sens/(1-spec) spec) x table: negative likelihood ratio + + a Disease - b T t Test - c d How less likelyy a negative g test result is in people with the disease compared to those without the disease LR- = c/a+c / d/b+d or LR- = (1-sens)/(spec) (1 sens)/(spec) LR10 = strong positive test result McGee: Evidence based Physical Diagnosis (Saunders Elsevier) % Bayesian reasoning Pre test 5% Post test 20% ? Appendicitis: McBurney tenderness LR+ = 3.4 % Fagan nomogram Do doctors use quantitative methods off test t t accuracy? ? „ Survey of 300 US physicians used Bayesian methods, used ROC curves, used LRs „ Why? …indices unavailable… …lack of training… …not relevant to setting/population …other other factors more important important… „ (Reid et al Academic calculations versus clinical judgements: practicing physicians’ use of quantitative measures of test accuracy Am J Med 1998) Appraising pp g diagnostic g tests Are the results valid? What Wh t are th the results? lt ? Will they help me look after my patients? Will the test apply in my setting? „ „ „ „ „ „ Reproducibility of the test and interpretation in my setting Do results apply to the mix of patients I see? Will the results change my management? Impact on outcomes that are important to patients? Where does the test fit into the diagnostic strategy? Costs to patient/health service? Reliability – how reproducible is the test? ? „ Kappa = measure of intraobserver reliability Test Kappa value yp Tachypnoea 0.25 Crackles on auscultation 0.41 52 0.52 Value of Kappa Strength of Agreement Pleural rub