BOARD REVIEW : EBM & PREVENTION

Jesse C James

Q & A: Harrisons I-1

• A physician is deciding whether to use a new test to screen for Disease X. The prevalence is 5%. Sensitivity 85% Specificity 75%. In a population of 1000, how many with X will be missed in screening?

• A 50• B 42• C 8• D 4• E 10

Q&A

• What is this question asking? How many people w disease have negative test?What is the expected number of false negatives? %FN=(1-sensitvity) or #FN= Prevalent cases-TP cases

• Prevalence = number of people with diseasePrevalence = 5% * 1000 = 50

• Sensitivity= 85% with disease will be True PositivesSens= .85*50 = 42.5 True PositivesFN = 50-42.5= 7.5 FN

Sensitivity

• The percentage of persons with the disease of interest who have positive test results= True-post/(True-post + False-neg) x 100 (HUH??)= True positives/All pts w disease (OK!!!)Tests that are very sensitive are clinically useful to

rule out a disease…because if you had it, you would be positive

IDEPENDENT of the prevalence of disease

Specificity• The percentage of persons without the

disease who have negative test results= True-neg/(True-neg + False-post) = True-neg/All patients with diseaseThe more specific the more likely persons without

the disease of interest will be excluded.Both sensitivity and specifity are independent of

prevalence

Q & D

• PREVALENCE: Prob (+ disease)• SENSITIVITY: Prob (True Positive) given

disease• SPECIFICITY: Prob (True Negative) given no

disease• PPV: Prob (+disease) given positive test• NPV: Prob (-disease) given negative test

Q & A: Harrisons I-1

• A physician is deciding whether to use a new test to screen for Disease X. The prevalence is 5%. Sensitivity 85% Specificity 75%. In a population of 1000, how many with X will be missed in screening?

• A 50• B 42• C 8• D 4• E 10

ANSWER

• The answer is C. 8• Prevalent cases 50• True positives=Prev Cases*Sens= 50*.85= 42.5• False negatives=Prev Cases-TP=7.5

2x2 Table

Q&A Harrison’s I-2

• How many patients were told erroneously that they have disease based on this test?

• A.713• B.505• C.237• D.42• E.8

ANSWER

• What is the question asking?How many without disease have a positive test?How many false positives are expected?Total without disease – TN cases= # False positives

• Prevalence = number of people with diseasePeople w/o disease = 1000-(5% * 1000) = 950

• Specificity= 75%of people without disease will be TN casesSpec(TN) cases= .75*950 = 712.5 TN casesFPcases = 950-712.5= 237 FP cases

ANSWER

• The answer is C. 237

Q&A: Harrisons I-3

• Drug X is investigated in a meta-analysis for its effect on mortality after a myocardial infarction. It is found that mortality drops from 10 to 2% when administered. What is the ARR?

• A. 2%• B. 8%• C. 20%• D. 80%

ANSWER

• ANSWER IS B 8%• ARR = Difference between risk in Exposed

(Exposed Event Rate) vs risk in Control (Control Even Rate)

• ARR= CER-EER• 10%-2%=8%• The RELATIVE RISK REDUCTION=ARR/CER=

8%/10%=80%

Q&A: Harrison’s I-4

• How many patients will have to be treated with drug X to prevent one death?

• A. 2• B. 8• C. 12.5• D. 50• E. 93

ANSWER

• The answer is C. 12.5• The NNT is equal to the inverse of the ARR• 1/ARR= 1/8% = 12.5

Q&A: Harrison’s I-6

• Which of the following regarding CAD in women is true?

A. Death rates for CAD for men and women have been increasing over the last 30 years.

B. The most common initial symptom of heart disease in women is angina.

C. Women with AMI are more likely than men to present with VTach.

D. Women in all age groups have lower mortality from MI than males do.

ANSWER

• The answer is B.• Mortality from CAD has been increasing among

women for the last 30 years and among men it has been decreasing.

• According to Framingham study angina is the most common presentation of coronary heart disease in women.

• Females w MI are more likely than males to present w cardiogenic shock and males are more likely to present w Vtach

Q&A: MKSAP14 FIM-4

• 23 yo woman evaluated for migraine occurring fives times per month wants to restart prophylactic medication regimen. The pt has already responded poorly to Beta-blockers and amitriptyline in the past. She wonders whether gabapentin will help. Which of the following sources is most likely to provide reliable information for answering this patient’s question?

A. Randomized controlled trialB. Case reportC. Case controlled studiesD. Systematic reviewsE. Drug information inserts

Study Types

• Case report/Case series: a description of single or multiple anecdotal presentation and management of diseases

• Case-control: typically identify patients with an outcome and then make retrospective survey of exposures. Matches cases with disease to controls without disease and check for exposures.

• Cohort study: prospective study that follows groups (the cohorts) divided by exposure to measure risk of development of outcome over time

• Systematic review: a literature assessment that identifies a question, eliminates/includes sources, appraises results and synthesizes/describes conclusions.

ANSWER• The answer is D: systematic review• Systematic reviews and meta-analyses are provided summaries of

voluminous information from multiple publications of original research. They can show where a body of literature has both consistencies and controversies and be generalized more reliably across populations.

• Single RCTs rarely provide definitive answers to broad clinical questions due to the difficulty in generalizing to a single patient and the probability of differences being due to chance alone (type I error).

• Case reports are clinical observations that should never be used to draw clinical conclusions.

• Case controlled studies are not randomized and prone to bias and typically describe the association between and exposure and an event.

Q&A: MKSAP14 FIM-7

• 19 yo F w RLQ abd apin and fever. Abd tender to palpation w/o rebound/guarding. Pelvic exam normal. From experience the probability of acute appendicitis is 50%. A positive abdominal CT has a likelihood ratio of 13.3 for the diagnosis of acute appendicitis. If the CT scan is positive for appendicitis what is the approximate increase in probability that the patient has appendicitis?

A. 5%B. 15%C. 30%D. 45%E. 60%

LIKELIHOOD RATIOS

• LR: considers both the sensitivity and specificity combined into a single measure of diagnostic effectiveness

• +LR= sensitivity/(1-spec)• Proportion of pts with disease that test positive versus

the prop of pts w/o disease who test positive• The greater the magnitude of a LR, the more useful the

test is for increasing the probability for confirming a target disease.– Positive LR of 2, 5, and 10 increase the probability of disease

by 15%, 30% and 45% respectively

ANSWER

• The answer is D: 45%

MKSAP14 FIM13

• 55 yo w cough and malaise that occurs multiple times per year. He has 40 pack-year history. On exam he is afebrile HR, RR, BP wnl. Cardiopulmonary exam is normal, chest clear w/o consolidation/wheeze and heart regular. Which of the following is the most appropriate initial smoking cessation management step during this visit?

• A. Recommend nicotine gum• B. Provide a clear, personalized message to the patient• C. Refer the patient to behavioral modification• D. Prescribe bupropion

ANSWER

• The answer is B. Provide a clear, personalized message to the patient

• Although buproprion, nicotine replacement, and behavioral therapy are appropriate adjunct interventions, however, using these without adequately assessing the patients readiness for behavioral change is premature.

• Brief interventions for as few as 1-3 min have been shown to result in an increased number of patients who quit and abstain from cigarette smoking.

MKSAP GIM6

• 25 yo woman evaluated during for routine exam, nonsmoker, social alcohol drinker, denies illicit drug history. She has had 3 sexual partners and is in a serious monogamous relationship. She has no history of STIs and takes OCP for pregnancy prevention. She has a scheduled Pap smear. Which of the following is most appropriate for this patient?

• A. Encourage sunscreen use• B. Prescribe multivitamin with folic acid• C. Screen for Chlamydia • D. Measure fasting plasma glucose

ANSWER• The answer is C: Screen for Chlamydia• CDC recommends annual screening for sexually active women

aged 25 and younger at increased risk for infection– New or multiple sexual partners– History or current symptoms of STI– History of unprotected intercourse

• Age <25 is strongest predictor in men and women• Benefit of counseling to patients w high sun exposure is unknown• A multivitamin w folic acid is recommended for pregnant women

to prevent neural tube defects but is not necessary in this patient she is not pregnant and on OCPs.

• FPG is not recommended for routine screening without risk factors for DM.

MKSAP 14 GM37

• 45 yo AAM is evaluated for concerns about prostate cancer. A close friend was recently diagnosed w extensive disease and has a poor prognosis. The patient asks if he should have a screening test for the disease. He has once per night nocturia and no hesitancy, freq, or dribbling. Which is the most appropriate plan of action?

• A. PSA measurement• B. PSA and DRE• C. Transrectal US• D. Random biopsies• E. Shared Decision making

ANSWER

• The answer is E: Shared Decision Making discussion risk and benefits.

• USPSTF recommends shared decision making on the potential risk and benefits of screening for prostate cancer.

• The PPV for PSA is 30%. Of the men with positive test, only a third actually have prostate cancer.

MKSAP 63

• 22 yo nursing school grad is evaluated for pre-employment. She has hx of SLE and no recollection of having chickenpox and her varicella titer is negative. Which is the most appropriate recommendation?

• A. No vaccination• B. Single vaccination (shortened series), clear for work• C. Single vaccination, delay work 4 weeks• D. Two-dose vaccination series over 6 weeks, clear for

work• E. Two dose vaccination series over 6 weeks, delay work

for 4 weeks.

ANSWER

• The answer is E: Two dose vaccination series over 6 weeks, delay work for 4 weeks.

• Due to her age and occupation she is at high risk for VZV infection an should be immunized w the usual two doses. The vaccine is recommended for all adults with no evidence of immunity.

• The live vaccine can cause shedding in the 4 weeks following injection so she should avoid patients who might be sick from exposure to her.

• A single dose is not advised for anyone

MKSAP14 HO-70• 30 yo woman G3P2 evaluated for routine exam, two years had

bilat tubal ligation. Took OCPs for 5 years between births. Healthy and w/o complaints. FH sig for maternal cousin diagnosed w OvarianCa at age 48. No other FH Brst or Ovrn Ca. Exam normal. Has friend of Askenazi Jewish descent w strong FH. Pt wants to know what she can do to reduce her own risk Brst/Ovrn Ca. Which of the following would be most appropriate?

• A. Routine Ca screening• B. Prophylactic bilat ooporectomy• C. CA-125 measurement• D. Restart OCPs• E. Routine daily vitamins

ANSWER

• The answer is A: routine screening.• Pt not a high risk for cancer so only age and

gender appropriate screening are indicated.• Pts friend most likely harbors BRCA1 gene

women with this abnormality are encouraged to use shared decision-making to consider prophylactic oophorectomy, chemoprophylaxis or routine CA-125 screening.

MKSAP HO-84• 59 yo woman is evaluated during a routine exam. Her family

history includes a sister who was recently diagnosed with advanced stage-ovarian cancer. The remainder of her medical and family history is noncontributory. Physical exam normal. Pt is concerned about her risk for developing ovarian cancer and ask what routine screening methods will decrease her risk. Which of the following is the most appropriate recommendation for ovarian cancer screening in this patient?

• A. No Screening test• B. Serum CA-125• C. Transvaginal US• D. Doppler ovarian exam

Answer

• The correct answer is A.• No screening tool has been shown to decrease

ovarian cancer mortality in general or in at risk risk populations.

• No clinical review organizations recommend routine ovarian ca screening.

• Predictive models developed show the available screening tools would have at most a small benefit.

GOOD LUCK GUYS!!!