Screening Tests Flashcards

(24 cards)

1
Q

What is the definition of a screening test?

A

Tests conducted on apparently healthy individuals, typically within groups or populations, to identify disease likelihood of developing disease or detect it early before symptoms appear.

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2
Q

What is the primary purpose of screening tests?

A

To identify the likelihood of developing a disease or detect it in its early stages, before symptoms appear.

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3
Q

Who is the target group for screening tests compared to diagnostic tests?

A

Screening tests target apparently healthy people (groups/populations), while diagnostic tests target sick individuals or those with positive screening results.

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4
Q

Are the results of screening tests typically considered final?

A

No, screening test results are not final and usually require follow-up. Diagnostic tests are often considered diagnostic.

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5
Q

How do screening tests generally compare to diagnostic tests in terms of cost and basis for treatment?

A

Screening tests are typically low cost and not a basis for treatment, while diagnostic tests may be expensive and are used as a basis for treatment.

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6
Q

List three important goals of screening programs.

A
  1. Treat diseases in their early stages. 2. Increase survival rates and minimize complications. 3. Improve the patient’s quality of life. (Also acceptable: Reduce disease development/progression, save costs, improve population mortality/morbidity).
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7
Q

What is Mass Screening?

A

Screening applied to whole populations or subgroups (e.g., universal blood pressure checks).

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8
Q

What is High-Risk or Targeted Screening?

A

Screening focused on groups with specific exposures or higher risk (e.g., Mantoux test for TB exposure).

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9
Q

What is Case-Detection or Opportunistic Screening?

A

Identifying potential cases during routine healthcare visits when individuals seek care for other reasons.

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10
Q

What is Multi-phasic or Multiple Screening?

A

Conducting several different screening tests simultaneously on the same occasion.

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11
Q

What are the key criteria for a good screening test mentioned in the document?

A

Valid, Reliable (Repeatable/Precise), Simple, Safe and Quick, Cheap, and Acceptable to the population.

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12
Q

What does it mean for a screening test to be ‘Valid’?

A

It accurately measures what it is intended to measure, assessed by comparing it to a ‘gold standard’ diagnostic test using metrics like sensitivity and specificity.

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13
Q

What does it mean for a screening test to be ‘Reliable’ (Repeatable/Precise)?

A

It gives consistent results when the test is performed more than once on the same individual under the same conditions.

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14
Q

Define Sensitivity in the context of screening test validity.

A

The ability of a test to correctly identify those with the disease. Formula: True Positives / (True Positives + False Negatives).

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15
Q

Define Specificity in the context of screening test validity.

A

The ability of a test to correctly identify those without the disease. Formula: True Negatives / (True Negatives + False Positives).

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16
Q

What does Positive Predictive Value (PPV) measure?

A

The probability that an individual with a positive screening test result truly has the disease. Formula: True Positives / (True Positives + False Positives).

17
Q

What does Negative Predictive Value (NPV) measure?

A

The probability that an individual with a negative screening test result is truly free of the disease. Formula: True Negatives / (True Negatives + False Negatives).

18
Q

What three main factors can affect the Reliability (Precision) of a screening test?

A
  1. Biological Variation (within the individual). 2. Instrument Variation (equipment differences). 3. Observer Variation (differences between readings by observers).
19
Q

List three essential characteristics a disease should have to be suitable for a screening program.

A
  1. It should be a significant health problem (high burden). 2. Its natural history should be understood. 3. It must have a detectable latent or early asymptomatic stage. (Also: Effective treatment exists, early treatment improves outcomes, facilities available, agreed treatment policy).
20
Q

What are the potential biases listed that can affect the evaluation of screening programs?

A

Lead Time Bias, Volunteer Bias, Length Bias, and Detection/Surveillance Bias.

21
Q

CA 09 24th
A novel screening test has been identified for screening test has been identified for screening the patients with HIV. Discuss how you would assess the validity and the reliability of this screening test (50 marks

A

Okay, here’s a simpler explanation based only on the provided summary:

To check if a new HIV screening test is good, we need to assess two main things:

  1. Is it Accurate? (Validity)
    • What it means: Does the new test correctly spot who has HIV and who doesn’t?
    • How to check:
      • Get a group of people (some with HIV, some without – confirmed by a very accurate ‘gold standard’ HIV test).
      • Use the new screening test on everyone in the group.
      • Compare the new test’s results to the gold standard results.
      • Calculate:
        • Sensitivity: How well the new test finds people who do have HIV (avoids false negatives).
        • Specificity: How well the new test clears people who do not have HIV (avoids false positives).
      • Goal: High sensitivity and high specificity mean the test is accurate (valid).
  2. Is it Consistent? (Reliability / Precision)
    • What it means: Does the new test give the same result if you repeat it on the same person (when their HIV status hasn’t changed)?
    • How to check:
      • Test the same person multiple times with the new test.
      • See if results are consistent.
      • Check for variation caused by:
        • The machine/kit: Are different machines or test batches giving different results? (Needs calibration/quality control).
        • The person reading it: Do different people (or the same person at different times) interpret the result differently? (Needs clear instructions/training).
      • Goal: A reliable test gives consistent results when repeated.

In short: We check if the test is accurate by comparing it to a perfect test (Validity) and if it gives consistent results when repeated (Reliability). Both are needed for a good screening test.

22
Q

List the factors that must be considered when deciding on starting a national screening programme for prostate cancer

A

Here are the factors that must be considered when deciding whether to start a national screening programme for prostate cancer:

  1. Disease Characteristics (from Section 8):
    • Significance: Is prostate cancer considered a significant health problem with a high burden in the nation?
    • Natural History: Is the natural progression of prostate cancer (from early stages to advanced disease without treatment) well understood?
    • Detectable Early Stage: Does prostate cancer have a detectable latent or early asymptomatic stage where screening could identify it before symptoms appear?
    • Effective Treatment: Is there an effective treatment available for prostate cancer?
    • Benefit of Early Treatment: Does evidence demonstrate that treating prostate cancer detected early through screening leads to better outcomes (reduced mortality/morbidity) compared to treating it only when symptoms appear?
    • Agreed Treatment Policy: Is there a nationally agreed-upon policy on who should receive treatment if diagnosed through screening?
    • Overall Benefit vs. Harm/Cost: Do the potential benefits of early detection and treatment outweigh the potential risks (e.g., side effects of treatment, anxiety from false positives) and the overall costs of the screening programme (tests, diagnosis, treatment)?
  2. Screening Test Characteristics (from Section 5, 6, 7):
    • Availability of a Suitable Test: Is there a suitable screening test available for prostate cancer (e.g., PSA test)?
    • Validity: Is the chosen test accurate?
      • Does it have high Sensitivity (correctly identifies men with prostate cancer)?
      • Does it have high Specificity (correctly identifies men without prostate cancer)?
      • What are its Positive Predictive Value (PPV) and Negative Predictive Value (NPV) in the target population?
    • Reliability: Is the test consistent and repeatable? (Considering biological, instrument, and observer variation).
    • Simplicity, Safety, Speed: Is the test simple to administer, safe for participants, and relatively quick?
    • Cost: Is the test cheap enough for large-scale national implementation?
    • Acceptability: Is the screening test procedure acceptable to the target male population?
  3. Resource Availability (from Section 8):
    • Diagnostic & Treatment Facilities: Are there adequate facilities available nationwide for follow-up diagnosis (if the screen is positive) and subsequent treatment?
  4. Overall Program Goals (from Section 3):
    • Will the program effectively contribute to goals like treating the disease early, increasing survival, improving quality of life, and potentially saving costs long-term at a population level?

Therefore, before launching a national prostate cancer screening programme, policymakers must carefully evaluate prostate cancer itself against the criteria for screenable diseases, assess the specific screening test(s) for validity, reliability, cost, and acceptability, ensure adequate healthcare resources are available, and confirm that the overall benefits justify the potential harms and costs, based on solid evidence (while being mindful of potential biases like lead time bias or length bias in studies).

23
Q

1.2 A population with a low prevalence was screened for hepatitis B using the triple panel test. The results are as follows. Sensitivity – 85% Specificity – 88% Positive predictive value – 35%1.2.1 Interpret the above results.(15 marks)1.2.2 Briefly describe the suitability of the triple panel test in screening hepatitis B. (15 marks)

A

Sensitivity (85%): The test correctly identies 85% of individuals who trulyhave Hepatitis B. It misses 15% of cases (False Negatives)

.○ Specicity (88%): The test correctly identies 88% of individuals who do nothave Hepatitis B. It incorrectly identies 12% of healthy individuals as positive(False Positives).

○ Positive Predictive Value (PPV - 35%): In this population (stated as lowprevalence), if a person tests positive, there is only a 35% probability that theyactually have Hepatitis B. 65% of positive results are False Positives.

○ Suitability: The test has reasonable sensitivity and specicity. However, in alow prevalence population, the PPV is quite low (35%). This means many people testing positive will not actually have the disease, leading tounnecessary anxiety and follow-up diagnostic tests. While it might be acceptable for some screening purposes (especially if follow-up testing is readily available and consequences of missing a case are high), the low PPV inthis context is a signicant drawback. Its suitability depends heavily on the program’s goals and the implications of false positives vs. false negativesThe suitability also depends on factors not provided in the results, such as the test’s Reliability (consistency), Simplicity, Safety, Speed, Cost, and Acceptability to the population. Without information on these, a complete assessment of suitability is not possible.

24
Q

Definitions:
Endemic Disease,Screening,Surveillance

A

Endemic Disease: Constant presence of a disease/agent at baseline levels ina specic geographic area/population (e.g., Dengue in SL)
Screening: Presumptive identification of unrecognized disease inasymptomatic individuals using tests/examinations (e.g., Pap smear forcervical cancer)
Surveillance: Continuous, systematic collection, analysis, interpretation, and dissemination of health data for planning, implementation, and evaluation of public health practice (e.g., monitoring inuenza cases).