Transcript How to pass the test

HOW TO PASS THE TEST
LECTURE 5 OF THE 6 PART MINI MED SCHOOL SERIES
Presenter: Sergiy Shatenko
DISCLOSURES
 I am a medical student
 This session is not intended to give you a diagnosis or replace you seeing your health professional
OVERVIEW
 Statistics (I will try to make this as fun as possible)
 Screening tests
 Common blood tests
QUIZ
1. How is a diagnostic test different from a screening test?
2. What does” Pap” stand for in Pap test?
3. What does hemoglobin A1C measure?
LEVELS OF DISEASE PREVENTION
 Primary – health protection and prevention of disease onset (“An apple a day keeps the doctor away” lecture)
 Secondary prevention – early detection of disease to minimize morbidity and mortality (This lecture)
 Tertiary prevention – treatment and rehabilitation of disease to prevent progression and permanent disability
DEFINITIONS
 Population – a collection of individuals who share a common trait
 Sample – selection of individuals from that population
 Sample size – contributes to the precision of the estimate
 Bias – trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions
that are systematically different form the truth ( Sampling bias, measurement bias, recall bias)
 Confounder – a variable that is related to both exposure and outcome that is not measured or is not distributed
equally between groups
BIAS IN SCREENING
 Lead-time bias – over-estimation of survival based on earlier detection
with screening (Example: Huntington’s disease)
 Length-time bias – overestimation of survival time due to sampling of
prevalent as opposed to incident cases (Example: Lung cancer)
DEFINITIONS
 Incidence – number of new cases in a population in a period of time
 Prevalence – total number of cases in a population in a period of time
INTERPRETING TEST RESULTS
Medical test
Disease
Test result
Present
Absent
Positive
24
14
Negative
6
56
30
70
38
62
INTERPRETING TEST RESULTS
 Sensitivity = true positive/(true positive + false negative)

= 24/30

= 80%
 Specificity = true negative/(true negative + false positive)

=56/70

=80%
Disease
Test result
Present
Absent
Positive
24
14
Negative
6
56
30
70
38
62
WHAT IT ACTUALLY MEANS
 SnOut

high sensitivity – if negative -> rule out
 SpIN

High specificity – positive -> rule in
 What clinicians want to know when applying the test to their patients
WHAT PATIENTS WANT TO KNOW
 Positive predictive value (PPV) = True positive/(True positive + False positive)
= 24/(24+14)
= 63%
 Negative predictive value (NPV) = True negative/(True negative + False negative)
= 56/(56+6)
= 90%
Disease
Test result
Present
Absent
Positive
24
14
Negative
6
56
PPV AND NPV ARE DEPENDENT ON PREVALENCE
 Same test if the disease is 10 times less prevalent:

PPV = 11%

NVP = 99.2%
Disease
Test result
Present
Absent
Positive
24
194
Negative
6
776
GOLD STANDARD TEST
 Best available test
 Not necessarily 100% sensitive and specific
 Used as a diagnostic test
 Sometimes not practical
LIKELIHOOD RATIO (LR)
 Positive likelihood ratio = sensitivity/(1-specificity) (= 4 in our example)
 Determines whether a test usefully changes the probability that a condition exists
 Used in the context of pre-test probability
 Changes the post-test probability
 If LR >1, there is increased probability that the disease state exists
 LR = 1, does not change the probability
 LR <1, decreases the probability
HOW A DIAGNOSIS IS MADE
Pre - test probability
LR test 1
Post - test probability
Pre - test probability
LR test 2
Post - test probability
EXAMPLE OF LIKELIHOOD RATIO FOR MIGRAINE
 POUND criteria

Pulsating

duration of 4-72 hOurs

Unilateral

Nausea

Disabling
 If 4 of the 5 criteria are met, the LR for migraine is 24
 if 3 are met, the LR is 3.5
 if 2 or fewer are met, the LR is 0.41
LIKELIHOOD RATIO FOR ACUTE CORONARY SYNDROME (HEART
ATTACK)
 Radiation to both arms LR+ 2.6, LR- 0.93
 Prior coronary artery disease LR+ 2.0, LR- 0.75
 ST elevation on ECG LR + 5.7-53.9, LR – 0.1
SCREENING
 Purpose of screening :
 Take asymptomatic individuals and divide them into high risk versus low risk group
 High risk group goes on to more diagnostic investigations
 Tries to catch the disease at an earlier stage
 NOT TO DIAGNOSE
TYPES OF SCREENING
 Mass screening – screening all members of the population for a disease (Example: Scoliosis)
 Selective screening – screening a specific subgroup of the population who are at risk (Example: Breast Cancer)
 Multiphasic screening – the use of multiple screening tests on the same occasion (Example: annual health check
up)
 Opportunistic screening – screening of persons who come to a health practitioner for some other purpose
(Example: screening for high blood pressure when a patient comes in for a flu shot)
CRITERIA FOR SCREENING TEST
 Disease

Should be serious

Natural history must be understood

Must have an asymptomatic stage that can be detected by a test

Early detection and intervention must result in improved outcomes

Goldilocks incidence (not too high, not too low)
CRITERIA FOR SCREENING TEST
 Screening test

High specificity and sensitivity

Safe, rapid, relatively inexpensive

Acceptable to providers and to populations
CRITERIA FOR SCREENING TEST
 Diagnosis and treatment

There is an available, effective, acceptable and safe treatment

Early treatment should be more effective than later
CRITERIA FOR SCREENING TEST
 Health Care system

Adequate capacity for reporting, follow-up, and treatment of positive screens

Cost effective

Sustainable program

Clear policy guidelines
CERVICAL CANCER SCREENING
 The Pap test (Papanicolaou Test)
 1 in 156 women will develop cervical cancer in their lifetime
 BC Cancer Agency screening guidelines

Women 25-69 should be screened every 3 years (recently changed)
WHAT ARE THEY LOOKING FOR?
POSITIVE PAP TESTS
BC Cervical cancer screening program report
WHAT ARE THE NEXT STEPS?
 Retest in 6 months X4 for patients with ASCUS/LSIL
 Colposcopy and/or colposcopy guided biopsy for patients HSIL/AGC/ASC-H
POST COLPOSCOPY
 PPV for Cervical intraepithelial neoplasia grade 3
or adenocarcinoma in situ is 4.6%

Premalignant changes with high
rate of progression
 PPV for invasive cancer 0.5%
 These numbers will change with
the new screening guidelines
PELVIC EXAMS IN WELL WOMEN
 American College of obstetricians and gynecologists recommend doing them yearly, however this is expert
opinion only
 American College of physicians recommends against doing them
 Canadian Task Force on Preventive Health Care recommended adopting the American College of Physicians
recommendation

Kauffman RP, Griffin SJ, Lund JD, Tullar PE.
Current recommendations for cervical cancer screening: do they render the annual pelvic examination obsolete? Med Princ Pract. 2013;22(4):313–22. - See more at:
http://www.cfpc.ca/ProjectAssets/Templates/Resource.aspx?id=777&amp;langType=4105&terms=pelvic+exam#sthash.nl3G86r8.dpuf
BREAST CANCER SCREENING
 1 in 9 women will develop breast cancer in their lifetime
 BC Cancer agency screening guidelines

all women women 50 – 74: every two years

40 – 49 talk to your doctor about the benefits and limitations of screening

40 – 74 with a 1st degree relative with breast cancer: every year

Younger then 40 if you have BRCA1 or BRCA2 mutation, or chest wall radiation or strong family history

75+ talk to your doctor about the benefits and limitations of screening
WHAT ARE THEY LOOKING FOR
 Looking for asymmetry, architectural
distortions, calcifications
BREAST CANCER SCREENING
 Sensitivity 87.9%
 Specificity 93.1%
 With a prevalence of under 1%
 PPV of about 6.3% (2.5% in 40-49 and 13.5% in 70-79)
WHAT ARE THE NEXT STEPS?
 Diagnostic mammogram
 Ultrasound
 Needle biopsy
 Open biopsy
 6% of those who have a
positive mammogram
actually have breast cancer
SELF BREAST EXAMS?
 Studies show that self-examinations don't save women's lives and that they can lead to unneeded tests, such as
biopsies. The Canadian Cancer Society recommends that all women be familiar with how their breasts look and
feel and to talk to their doctors about any changes
 Healthlink BC: https://www.healthlinkbc.ca/health-topics/hw3791
COLORECTAL CANCER SCREENING
 4.4% of people will get colon cancer in their lifetime
 BC Cancer agency screening guidelines

Men and women ages 50-74 should get screened using the FIT test

Men and women ages 50-74 with a family history or personal history of adenomas should get colonoscopy screening
WHAT ARE THEY LOOKING FOR?
 FIT test AKA Fecal immunochemical test

Detects hemoglobin in the stool
 Colonoscopy
COLON CANCER SCREENING
 4.8% of those screened had positive result
 After a colonoscopy

4% PPV for colorectal cancer

60% PPV for adenoma
TERMINOLOGY
Epithelium
Benign
Malignant
Glandular
Adenoma
Adenocarcinoma
Transitional
Transitional papilloma
Transitional cell carcinoma
Liver
Adenoma
Hepatocellular carcinoma
Skin
Papilloma
Squamous cell carcinoma
Nevus
Melanoma
Basal cell carcinoma
Bone
Osteoma
Osteosarcoma
Fat
Lipoma
Liposarcoma
Cartillage
Chondroma
Chondrosarcoma
Smooth muscle
Leiomyoma
Leiomyosarcoma
“Striped” muscle
Rhabdomyoma
Rhabdomyosarcoma
Vessels
Angioma
Angiosarcoma
ADENOMAS ARE NOT MALIGNANT BY DEFINITION, WHAT’S THE
BIG DEAL?
 Vast majority of colorectal carcinomas are adenocarcinomas
 These are often preceded by adenomas
 Adenomas can be identified and removed during colonoscopy
PROSTATE CANCER SCREENING
 1 in 6 males will develop prostate cancer
 Not a population screening test
 BC cancer agency recommendations

Digital rectal exam (DRE) should be done annually in men 50-70

Digital rectal exam should be done if obstructive urinary symptoms are present

PSA (Prostate specific antigen) recommended if suspicious DRE or suspicious urinary symptoms
DIGITAL RECTAL EXAM
WHAT THEY ARE LOOKING FOR?
 Digital rectal exam

Feeling the prostate for any hard masses or irregularities
 Prostate specific antigen

Blood test for a glycoprotein that the prostate releases

Checking to see if the levels are above normal
PROSTATE CANCER SCREENING
 DRE

Sensitivity 59%

Specificity 94%

24% Positive predictive value
 PSA (4.0 ng/mL)

Sensitivity 21%

Specificity 91%

PPV 25% (40-60% if >10 ng/mL)
 Next steps?

Biopsy

MRI
MOVEMBER FOUNDATION
 Prostate cancer
 Testicular cancer
 Men’s health and suicide prevention
COMMON MEDICAL TESTS AND HOW THEY WORK
 Hemoglobin A1c
 CBC
 Iron
 Thyroid
HEMOGLOBIN A1C
 Measure of the percentage of hemoglobin that has been altered by glucose (glycosylated)
 Indirect measurement of 3 month average blood glucose

Life span of a red blood cell is 60-120 days
 Can now be used to diagnose diabetes (>6.5%)
 Advantages: provides an average, no need to fast
 Disadvantages: provides an average
COMPLETE BLOOD COUNT (CBC)
 Most commonly ordered test
WHAT DOES IT TELL YOU
 White blood cells

Increased in: infection, immune reaction, drugs,
bone marrow disease

Decreased in: infection, drugs, bone marrow disease
 Hemoglobin

Increased in: lung disease, heart
disease, doping

Decreased in: nutrient deficiency, liver/kidney disease,
cancer
 Mean cell volume

Helps differentiate the different types of anemia
 Platelets

If low Increased bleeding risk

Causes: medications, some infection, pregnancy, cancer
IRON
 Ferritin – storage form of iron, a measure of iron reserves
 Iron in the blood

Serum iron

Total Iron Binding Capacity

Transferrin saturation
FERRITIN
SERUM IRON AND TOTAL IRON BINDING CAPACITY
THYROID
 Thyroid stimulating hormone
 Pituitary is the sensor

Releases TSH to regulate thyroid
function
A CLINICAL SCENARIO
 A patient comes in complaining of fatigue
 Started slowly over the past few months
 Patient looks pale
Diagnosis? Anemia
105