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Robert S. Galen, M.D., M.P.H. Professor and Head, Department of Health Administration,

The Predictive Value of Laboratory Tests: Past, Present and Future. Robert S. Galen, M.D., M.P.H. Professor and Head, Department of Health Administration, Biostatistics and Epidemiology College of Public Health University of Georgia Athens, Georgia, USA 30604. Athens. Atlanta. New York.

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Robert S. Galen, M.D., M.P.H. Professor and Head, Department of Health Administration,

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  1. The Predictive Value of Laboratory Tests: Past, Present and Future Robert S. Galen, M.D., M.P.H. Professor and Head, Department of Health Administration, Biostatistics and Epidemiology College of Public Health University of Georgia Athens, Georgia, USA 30604

  2. Athens Atlanta New York Chicago 60 miles northeast of Atlanta Los Angeles Dallas Atlanta United States State of Georgia LOCATION

  3. HISTORY The Arch, Symbol of UGA UGA The University of Georgia January 27, 1785 America’s oldest state chartered university Chartered by Georgia General Assembly

  4. SANFORD STADIUM UGA Quarterback, D.J. Shockley UGA Mascot, UGA VI Aerial photo of Sanford Stadium, holds over 92,000 cheering fans

  5. Evaluating the Usefulness of Screening Tests • Sensitivity, Specificity, Predictive Value • Effects of pre-test probability on predictive value • Trade-offs in choosing different cut-off values • Trade-offs in choosing test combinations • Series and Parallel Testing • When to test ? • Which test is best ? • What does the result mean?

  6. Predictive Value Table

  7. Measures of the Validityof Tests Sensitivity Specificity Predictive value (+) Predictive value (-) Accuracy (efficiency)

  8. TP TP+FN TN TN+FP TP TP+FP

  9. Effect of prevalence on predictive value when sensitivity and specificity equal 95%

  10. Effect of prevalence on predictive value when sensitivity and specificity equal 99%

  11. Sensitivity and Specificity of Anti-HIV Tests in One Study

  12. Coin flip data arranged in tabular format

  13. Combination testing for hypothetical data

  14. ROC Curves

  15. Area under the ROC curve = 0.661 Standard error = 0.041 95% Confidence interval = 0.587 to 0.729 P (Area=0.5) = 0.0001

  16. Predictive Value

  17. IN MEMORIUM Bayes, Reverend Thomas. An essay toward solving a problem in the doctrine of chance. Philo. Trans. Roy. Soc. 53: 370- 418, 1763.

  18. The HIV Epidemic Laboratory advances in the predictive value of tests can drive clinical applications and improve quality of care: a) protecting the nation’s blood supply b) screening high risk patients c) screening all pregnant women d) screening everyone ? There are some challenges, however, as tests improve. The best test may not always be the most useful in a particular clinical situation.

  19. Awareness of Serostatus among Persons with HIV, United States Number HIV infected850,000 - 950,000 Number unaware of their HIV infection 180,000 - 280,000

  20. HIV Testing Challenges “In the United States, 32 % of the people who test positive don’t come back for their results.” Dr Bernard Branson, CDC

  21. Advancing HIV Prevention: New Strategies for a Changing Epidemic • Four priorities: • Make voluntary HIV testing a routine part of medical care • Implement new models for diagnosing HIV infections outside medical settings • Prevent new infections by working with persons diagnosed with HIV and their partners • Further decrease perinatal HIV transmission MMWR April 18, 2003

  22. Four FDA-approved Rapid HIV Tests

  23. OraQuick Advance HIV-1/2 • CLIA-waived for finger stick, whole blood, oral fluid; moderate complexity with plasma • Store at room temperature • Screens for HIV-1 and 2 • Results in 20 minutes

  24. Obtain finger stick specimen…

  25. Insert loop into vial and stir

  26. Collect oral fluid specimens by swabbing gums with test device. Gloves optional; waste not biohazardous

  27. Insert device; test develops in 20 minutes

  28. Reactive Control Positive HIV-1/2 Positive Negative Read results in 20 – 40 minutes

  29. Remember the tradeoffs… • Good News: More HIV-positive people receive their test results. • Bad News: Some people will receive a false-positive result before confirmatory testing.

  30. Predictive Value, Positive Test OraQuick Reveal Single EIA Uni-Gold HIV Prevalence 10% 99% 92% 98% 97% 5% 98% 85% 96% 95% 2% 95% 69% 91% 87% 1% 91% 53% 83% 77% 0.5% 83% 36% 71% 63% 0.3% 75% 25% 60% 50% 0.1% 50% 10% 33% 25% 99.9% 99.1% 99.8% 99.7% Test Specificity Positive Predictive Value of a Single Test Depends on Specificity & Varies with Prevalence

  31. HIV Screening with OraQuick in Labor and Delivery: the MIRIAD Study • Testing of pregnant women in labor for whom no HIV test results are available; 16 hospitals in 6 cities: Atlanta, Baton Rouge, Chicago, Miami, New Orleans, New York • Results: • 4849 women screened • 34 (0.7%) new HIV infections identified • Sensitivity 100 % Specificity 99.9 % • Positive Predictive value: OraQuick 90%; EIA 76% Bulterys et al, JAMA 2004; 292: 219-223

  32. USPSTF Recommends Screening All Pregnant Women for HIV “The United States Preventive Services Task Force continues to recommend screening all adolescents and adults at high risk for HIV and now also recommends screening all pregnant women.”

  33. USPSTF Recommends Screening All Pregnant Women for HIV Evidence is good that pregnant women find recommended regimens of highly antiretroviral therapy (HAART) to be acceptable, and that HAART significantly lowers rates of mother-to-child transmission. Early diagnosis of maternal HIV infection also facilitates discussion of elective cesarean section and avoidance of breast-feeding, which may lower HIV transmission rates.

  34. HIV Screening with OraQuick in Labor and Delivery: the MIRIAD Study • The CDC now recommends routine rapid HIV testing using an opt-out approach (ie, a woman is informed that HIV testing will be routinely done during labor if her HIV status is unknown but she may decline testing). • Rationale: there is a brief window of opportunity for interventions to decrease HIV transmission to the newborn Bulterys et al, JAMA 2004; 292: 219-223

  35. HIV Screening with OraQuick in Labor and Delivery: the MIRIAD Study • “In many settings, including in the developing world, pregnant women with unknown HIV status are often seen by clinicians for the first time during labor. • Rapid testing during labor can enable pregnant women with undocumented HIV status to learn their HIV infection status so they can receive antiretroviral prophylaxis and be referred for comprehensive medical care and follow-up.” Bulterys et al, JAMA 2004; 292: 219-223

  36. Nucleic acid amplification testing • Two steps forward and one step back: • Do antibody tests miss cases that could otherwise be diagnosed? • We know there have been false-negatives during the acute infection period. How bad is the problem ?

  37. Nucleic acid amplification testing • “ In this study, we found that antibody tests alone detected only 96 percent of HIV infections, as compared with an algorithm that included nucleic acid amplification tests to detect acute HIV infections.” Pilcher et.al. NEJM 2005; 352: 1873-83

  38. Nucleic acid amplification testing • “The addition of nucleic amplification testing to an HIV testing algorithm significantly increases the identification of cases of infection without impairing the performance of diagnostic testing. The detection of highly contagious, acutely infected persons creates new opportunities for HIV surveillance and prevention.” Pilcher et.al. NEJM 2005; 352: 1873-83

  39. Nucleic acid amplification testing • “ We believe that the work that has been done to date…is now sufficient to allow us to conclude that this form of testing should be a standard tool for the prevention and surveillance of HIV infection and for the care of infected persons.” Pilcher et.al. NEJM 2005; 352: 1873-83

  40. Nucleic acid amplification testing • What is the value of a test, if patients don’t get the result ? • In some clinical situations the best test may not solve the problem! • Tests must be selected in the clincial context they will be used, not in a vacuum!

  41. Routine Population-Wide HIV Screening May Be Cost-Effective • “The findings of Paltiel et al. and Sanders et al. show that, given the availability of effective therapy and preventive measures, it is possible to improve care and perhaps influence the course of the epidemic through widespread, effective, and cost-effective screening.” Bozzette S.A. N.E.J.M. 2005; 352: 620-621.

  42. Routine Population-Wide HIV Screening May Be Cost-Effective • “Failure to implement widespread routine screening for HIV infection represents a critical disservice to patients who are currently infected, those at risk for infection, and the future health of the nation.” Bozzette S.A. N.E.J.M. 2005; 352: 620-621.

  43. What is a risk factor? • The traits, factors, and characteristics that predispose to the development of atherosclerosis have been collectively termed “risk factors.” • Not all risk factors are useful laboratory tests

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