Question 151#

In a study to evaluate a test as a screen for the presence of a disease, 235 of the 250 people with the disease had a positive test and 600 of the 680 people without the disease had a negative test.

Based on this data, the specificity of the test for the disease is: 

A. 235/250 = 94%

Correct Answer C:

The specificity of a test for a disease is the proportion or percentage of those without the disease who have a negative test.  

Specificity = number of true negatives / (number of true negatives + number of false positives) 

= 600 / (600 + 80) 

= 600 / 680 

= 88% (choice C) 

→ In this case, 235/250 = 94% (choice A) is the sensitivity, i.e., the proportion of those with the disease who have a positive test.

→ 15/250 = 6% (choice B) is the false-negative rate.

→ 80/680 = 12% (choice D) is the false-positive rate.

→ 15/80 = 19% (choice E) is the ratio of false-negative tests to false-positive tests, a meaningless ratio.  

The predictive values of positive and negative tests are extremely important characteristics of a screening test. Determination of these values requires knowledge of the prevalence of the disease in the population screened, as well as the sensitivity, specificity, and false-positive and false-negative rates. Since the prevalence of most diseases is low, the percentage of those with a positive test (the predictive value of a positive test) is relatively low, even when sensitivity and specificity are high. When prevalence is low, however, the predictive value of a negative test is very high and may approach 100%.  

Question 152#

The specificity of a screening test is best described as the proportion of persons:

A. With the condition who test positive

Correct Answer E:

A screening test’s specificity is the proportion of persons without the condition who test negative for that condition (choice E). In other words, it is a measure of the test’s ability to properly identify those who do not have the disease.  

→ Conversely, the sensitivity of a screening test is the proportion of those with the condition who test positive (choice A).

→ The other options listed describe false-negatives (choice B), accuracy (choice C), and false-positives (choice D).

Question 153#

Examples of secondary prevention would include all of the following, except:

A. Pap smear for cervical cancer

Correct Answer D:

Primary Prevention is trying to prevent a problem before it shows any signs of appearing. Goal is to remove risk factors.  

Examples: In people with no signs of heart disease, educating them on exercise and diet, and urging them not to smoke. Giving immunizations to kids so that they don’t get the diseases. 

Secondary Prevention is dealing with the early signs of a potential problem. Designed for early detection and treatment. 

Examples: Intervening with people who have high blood pressure (an early condition that might lead to heart disease), through medication or other methods. Screening higher risk patients with tests (eg cholesterol levels for obese patients, colonoscopy for those with positive family history of colon cancer). 

Tertiary Prevention: is treating people who have the full, actual illness.

Examples: Performing heart surgery on people with advanced disease. Giving rehab to someone who has had a stroke or been in an accident.

Question 154#

Which one of the following community health programs best fits the definition of secondary prevention? 

A. A smoking education program at a local middle school

Correct Answer B:

Prevention traditionally has been divided into three categories: primary, secondary, and tertiary.

• Primary prevention targets individuals who may be at risk to develop a medical condition and intervenes to prevent the onset of that condition (e.g., childhood vaccination programs, water fluoridation, antismoking programs, and education about safe sex). (choice A and choice C)
• Secondary prevention happens after an illness or serious risk factors have already been diagnosed. The goal is to halt or slow the progress of disease (if possible) in its earliest stages; in the case of injury, goals include limiting long-term disability and preventing re-injury. (e.g., routine Papanicolaou smears, and screening for hypertension, diabetes, or hyperlipidemia). (choice B)
• Tertiary prevention focuses on helping people manage complicated, long-term health problems such as diabetes, heart disease, cancer and chronic musculoskeletal pain. The goals include preventing further physical deterioration and maximizing quality of life (e.g., cardiac or stroke rehabilitation programs, chronic pain management programs, patient support groups). (choice D and choice E)

Question 155#

Screening for breast cancer in high risk patients is considered:  

A. Passive prevention

Correct Answer C:

Disease prevention strategies:

With respect to healthcare, disease prevention strategies can be broken down into 3 categories:

1. Primary prevention, option (b), is a strategy put in place before disease occurs (e.g. immunization, smoking cessation programs).
2. Secondary prevention, option (c), involves establishing screening methods to detect disease at (hopefully) an early stage (e.g. mammograms, pap smears).
3. Tertiary prevention (d) is treating an existing disease to prevent or retard further complications from arising (e.g. prescribing ACE inhibitors for hypertension).

Option (a), passive prevention strategies are measures put in place that protect a person without their active efforts, e.g. having airbags standard in cars. Whereas, active prevention (e) are measures the individual must do on their own accord such as wearing a seat belt. 

PEARL: Screening is a secondary prevention measure.