4 Methods of Diagnosis II

Question 1

Objective 1. Understand basics of disease in screening a population

Contrast Screening and diagnostic testing

Answer 1

Screening: Testing a healthy (asymptomatic) population to look for people at high risk of some disease
If positive, can do further tests for confirmation and try to prevent it from happening or delay onset/complications
Diagnostic testing: intended for those showing symptoms in need of a diagnosis

Question 2

SLIDE 14 IMAGE Describe how normal ranges are constructed

Answer 2

Assuming a rooughly Gaussian distribution A population of 120 +/- samples is required. Once tested, the results are compared and the highest and lowest values (outliers) are eliminated. The range is then established from the remaining sample values.
- values within 95% of the mean are considered normal which means 5% of otherwise healthy people will have abnormal results

Question 3

Define:
* True Negative
* False Negative
* True Positive
* False Positive

Answer 3

• True Negative* Patient does not have the disease and tests neg
• False Negative* Patient has the disease but tests NEG
• True Positive: Patient does have the disease and Tests POS
• False Postive: Pt doesn’t have the disease but tests positive

Question 4

How do you calculate sensitivity of a lab test? What is Sensitivity?

Answer 4

Sensitivity = TP/(TP+FN) X100%
TP = True Pos
FN = False Neg
ie specificity equals the number of people who tested positive while being sick divided by everyone who tested positive.
Sensitive = Good at sensing disease; probability that the test will be positive in the presence of disease ( hits over hits+misses)

Question 5

How do you calculate Specificity?
Define Specificity

Answer 5

Specificity = TN / (TN+FP)
- Specificity describes the probability that the test will be negative in the absence of disease
- More specific = more likely a true neg person will test neg

Question 6

What is SNOUT?

Answer 6

• SNOUT:
• Sensitivity
• Sn = Sensitive
• N = Negative
• Out = RULES OUT
• ie a highly sensitive test giving a negative result **rules out **the disease

Question 7

What is SPIN?

Assessing lab test performance

Answer 7

• SPIN
• Sp - specificity
• P = Positive
• IN = Rules in
• ie a highly specific test giving a positive result rules in the disease

Question 8

Define incidence and prevalence.

Answer 8

Incidence = Number of new cases in a fixed time period (usually yearly)
Prevalence = How many people actually have the disease at any point in time (more aggressive will have lower prevalence because of high mortality)

Question 9

➢ List ideal conditions for screening.

Answer 9

• Screening must provide a benefit to the patient
• Effect of treatment is available,
• Screening test is not harmful
• To be Effective:
• Target population has significant prevalence of the disease
• A suitable screening test is available
• Appropriate target population must be identified
• Test must be available to the target population

Question 10

➢ List ideal characteristics of a screening test.

Answer 10

1. Inexpensive
2. Noninvasive
   * 3. expensive and/or invasive tests sometimes acceptable
3. Excellent sensitivity and specificity
   * 4. Often acceptable to use less specific test as long as a VERY SPECIFIC diagnostic test is used
4. **Positive screening test is usually followed up with a diagnositic test **
   * 5. must have high sensitivity and specificity