Intro to Diagnostics

How does diagnostics play a role in screening?

identify risk factors for disease and to detect occult disease in asymptomatic individuals

where do we get the most important clinical information from

patient history and physical exam

how does diagnostics play a role in diangosis?

helps establish or excluded the presence of disease in a symptomatic individual. It can help early diagnosis, assist in a differential diagnosis, and help determine stage or activity of disease

how does diagnostics play a role in patient management?

helps evaluate the severity of the disease. Allows for estimation of prognosis, monitors the course of disease, detects disease recurrence, and selects drugs and adjacent therapy

what factors influence diagnostic test performance?

test performance including timing, container/ tube, and site. patient preparation- wether the patient is fasting, their posture, physical activity level, and compliance. specimen collection- proper labeling, correct time of test, and proper handling and storage.

considerations of diagnostics

• weigh the potential benefits agaisnt the poteintial cost and adverse effects

• some diagnsotics carry of risk of morbidity or mortality to patients

• persnalized medicine

• potential discomfort

• results may mandate additional testing or follow up

• false positives can lead to incorrect diagnosis or further unnecessary testing

Cost of diagnosis

• total cost may be high

• patient out of pocket may be prohbititve

• cost effectiveness may be unfavorable

Criteria for screening test

• characteristic of the population

• characteristic of the disease

• characteristic of the test

characteristics of the population

• sufficently high prevalence of disease

• likely to be compliant with subsequent test and treatments

Characteristics of the disease

• significant morbidity and mortality

• effective and acceptable treatment readily available

• presymptomatic period detectable

• improved outcome from early treatment

Characteristics of the test

• good sensitivity and specificity

• low cost and risk

• confirmatory test available and practical

performance of diagnostic test

• timing

• medium

• site

patient preparation

• fasting, certain electrolyte restrictions

• posture

• physical activity level prior or during a test

• compliance

specimen collection

• proper labeling

• correct timing of test

• correct medium for collection

• proper site and technique

Accuracy

accuracy of a lab test is its correspondance with the true value

Precision

a measure of a test productibility whne repeated on the same sample

Reference Intervals

used on test with quantitative results. Normally 95% of healthy people.

Sensitivity

• rules out disease.

• you want a highly sensitive test- catches almost everyone that has the disease.

• If this highly sensitive test is negative I can be confident my patient probably does not have the disease

Specifcity

• rules in a disease.

• if the test is positive the disease is present.

Prevelance

the proportion of individuals in a population having a disease or characteristic

Positive Predictive Value

the probability of having the disease if a test is positive

Negative Predictive Value

probability that an individual is actually diseae free if the test is negative

True Positive

patient is sick and the test catches it

False Positive

the test is positive but patient does not have the disease (cries wolf)

false negative

the test misses the disease

true negative

healthy patient gets a normal test