R.M.Dorizzi, Strumenti per interpretare gli esami di laboratorio? Forlì, 9 ottobre 2012

Transcript

1 1 Half of what you are taught as medical students will in 10 years have been shown to be wrong. And the trouble is, none of your teachers know which half. Sydney Burwell, Dean Harvard Medical School

2 AST aumentata Epatopatia AST aumentata Epatopatia 4

3 Medicine is a science of uncertainty and an art of probability Sir William Osler Sensitivity 95% Specificity 95% Prevalence 1/1000 Casscells W, et al.1978; 299:

4 22 (37%) (45%) 11 (18%) 27 Casscells W, et al.1978; 299: Fagan TJ. Nomogram for Bayes theorem. 1975; 293: 257 8

5 Ipotiroidismo: TSH Se= 99.5% Sp= 99.5% LR+ = 199 prevalenza Ambulatorio MMG 0.01 Ambulatorio Endocrinologico Ipertiroidismo: TSH Se= 96.0% Sp= 99.0% LR+ = 95 prevalenza Ambulatorio MMG 0.01 Ambulatorio Endocrinologico

6 LR+ = probability of an individual with the condition having a positive test probability of an TP/ individual without the FP condition having a positive test 11 LR- = probability of an individual with the condition having a negative test probability of an FN/ TN individual without the condition having a negative test 12

7 Positive likelihood ratio (LR+) how much the probability of disease increases if the test is positive Negative likelihood ratio (LR-) how much it decreases if the test is negative

8 In the authors opinion, reporting LR with results is the most important step toward the practice of evidence-based laboratory medicine. 15 Tools such as Forest plots, ROC curves or nomogram presentations such as Fagan s diagram can assist in communicating information. 16

9 17 As we discussed, the normal range that is typically reported with a patient s results is ill defined, of limited value, and potentially misleading. 18

10 Finally, laboratories can assist in the practice of EBM by including LRs from the best available evidence when reporting test results. 19 Several convenient alternatives to this tedious calculation are available, including online calculators, handheld computers, and nomograms 20

11 The inclusion of LRs with test results would be a monumental step toward the practice of evidencebased laboratory medicine

12 We are convinced that the lamented chasm between the theory of EBLM and the applications of its tools (such as LRs) could be rapidly filled. 23 Likelihood ratio LR+ > 10 LR- < < LR+ < <LR- <0.2 2 < LR+ < <LR- <0.5 1 < LR+ < <LR- <1.0 Modificano in modo spesso conclusivo la probabilità di malattia Modificano in modo discreto la probabilità di malattia Modificano modestamente la probabilità di malattia Modificano scarsamente la probabilità di malattia e solo di rado sono importanti. 24

13 25 Although this method is inaccurate for pretest probabilities < 10% or > 90%, these polar extremes of probability indicate diagnostic certainty for most clinical problems, making it unnecessary further tests 26

14 LR 2 increases probability 15% 5 increases it 30% 10 increases it 45% between 0 and 1 simply invert 2, 5, and 10 (1/2 = 0.5, 1/5 = 0.2, 1/10 = 0.1) 27 It is easy to recall at the bedside by simply remembering 3 specific LRs 2, 5, and 10 and the first 3 multiples of 15 (15, 30, and 45). 28

15 29 A smart mother often makes a better diagnosis than a poor doctor. August Bier