Chapter 7: Postanalysis Flashcards by Kirby Leij Santos

Indicate problem with the specimens or an issue with the result
Prevent the release of erroneous laboratory

Alarms and Flags

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Additional Steps in Flagging Specimens

by automated instrument itself
by specialized middleware
by laboratory information system

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Flags for Problem Specimen

sample contain amounts inadequate for reliable analysis

- presence of high concentration of interfering substances in the specimen

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instrument that can often analyze more than 100 samples per hour

Automated Cell Counters

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What type of samples can be reported immediately?

Normal Sample or Samples that show Quantitative Abnormalities

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Flagged for preparation of blood smear and further evaluation

Samples that could contain qualitative abnormalities

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What happens to an analyte concentration outside the validated linear range?

increase in signal linearity related to inc. in conc.
above the linear range, the machine dilutes and renanalyze sample
below LR, sample is reported as “less than the limit of detection”

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The process of conparing a current laboratory result with results obtained on a previous specimen from the same patient

Delta Checks

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Types of Errors Detected by Delta Checks

preanalytic and analytic issues

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May not be readily detectable

Must be reported immediately to a healthcare provider

Critical Values

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Required rapid communication of laboratory results

Federal Law, Regulatory Agencies, and Joint Commission

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Develops a crticial values policy that meets the needs of the patients and staff served by the laboratory

Medical Director of the Laboratory

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Definition of Reference Intervals

Laboratory Results vs Reference or Normal Range

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Range of values into which 95% of non-diseased individuals will fall
*some of these analytes is defined as “greater than” or “less than” a certain value
some have been defined by prof. org. w/out adherence to the 95% rule

Reference Ranges

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Does not require reference intervals except if the patient population was clearly distinct and exhibited range of values

Standardization

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The Joint Committee for Traceability in Laboratory Machine establishes process for standardization by:

Identifying
Reviewing against agreed criteria
Publishing list(s) of Higher Order Certified Reference Materials and Reference Measurement Procedures

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Calibrating and using materials traceable to isotope dilution mass spectrometry reference measurement procedure

Reduce Interlaboratory Variability

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Factors that Influence Reference Ranges

Age
Genetic background
Exposure to environmental factors
Sample collection container
Sample transport
Time between specimen collection and analysis
Sample storage before analysis

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Determination of Reference Ranges

Testing at least 120 SAMPLES from nondiseased individuals in each “partition”
Transference
Verication by another lab’s or the manufacturer’s reference interval if the analyte was not previously tested for the lab

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Verification of a reference interval that was previously established for a different method

Transference

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Result of assay imprecision

Analytic Variability

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Due to biologic changes that cause analyte levels to fluctuate over time

Intraindividuality Variability

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Occurs becauuse of factors specific to individual patients

Interindividuality Variation

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The sum analytic and intraindividuality variability

Study These Flashcards

Random Variability

Used for disease classification (positive or negative)

Threshold

Based on the results that are seen in 95% of the healthy population

Reference Range / Interval

Determined by comparing test's ability to discern true disease from nondisease

Diagnostic Accuracy

Used to discern true disease from nondisease

Diagnostic Gold Standard

The non-overlapping areas of the two patient distribution.

True Results

Classified as Abnormal

True Positive (TP)

Classified as Normal

True Negative (TN)

Used to discriminate disease from normal populations

Single Cutoff

The overlapping areas of the two patient distribution

False Results

INCORRECTLY classified as NORMAL

False-Negative (FN)

INCORRECTLY classified as ABNORMAL

False-Positive (FP)

The error of True Positive

False-Negative

The error of True Negative

False-Positive

Measures of diagnostic accuracy | Indicators in distinguishing the presence and absence of disease at a chosen cutoff

Sensitivity and Specificity

● The ability of a test to detect disease. ● The proportion of persons with the disease. ● TRUE POSITIVE (TP) ● Identifies a greater proportion of persons with the disease.

Sensitivity

● The ability of a test to detect the absence of disease ● The proportion of persons without the disease. ● TRUE-NEGATIVE (TN) ● Excludes a greater proportion of persons without the disease.

Specificity

Effect of Altering the Test Cutoff

● Altering the cutoff changes a test’s sensitivity and specificity. ● An inverse relationship between SENSITIVITY AND SPECIFICITY is noted.

For tests where high values indicate disease, lowering cutoff (cutoff line moved to the left) will lead to more diseased patients being classified as abnormal.

HIGH SENSITIVITY

If the cutoff is raised (the cutoff line moved to the right), more non-diseased patients are classified correctly.

HIGH SPECIFICITY.

The Need for High Sensitivity vs High Specificity

● False results such as FP (false-positive) and FN (false-negative) can lead to misdiagnosis and inappropriate clinical management. ● SENSITIVITY should be HIGH to capture the majority of cases. (Lowering cutoff) ● SPECIFICITY can be INCREASED to exclude all persons without the disease. (Increasing cutoff).

 sometimes referred to as positive predictive value  may be understood as the probability that a positive test indicates disease  it is the proportion of persons with a positive test who have truly the disease.

PREDICTIVE VALUE OF A POSITIVE TEST

 Referred to as negative predictive value  Is the probability that a negative test indicates absence of disease  It is the proportion of persons with a negative test who are true without disease

PREDICTIVE VALUE OF A NEGATIVE TEST

Relationship of Prevalence and Posttest Probability

The higher the prevalence, or pretest probability, the higher the posttest probability, or predictive value of a positive test.

- Shows that sensitivity and specificity influence the predictive value. - Describes the relationship between posttest and pretest probability of disease or no disease based on the sensitivity and specificity of the test

Bayes Theorem

Also known as priori probability, is the prevalence of the disease in the patient’s clinical setting - used in conjunction with the characteristics of diagnostic accuracy as summarized in the sensitivity and specificity of the test.

Pretest probability

Also known as posteriori probability, is the probability of disease in the posttest situation and is commonly referred to as the predictive value of the test.

Posttest probability

● A convenient measure that combines sensitivity and specificity into a single number specificity into a single number. ● An assessment of test performance, and not of disease status, in the patient being tested.

Likelihood Ratio

The LR+ is the ratio of two probabilities: the probability of a positive test result when the disease is present (TP) divided by the probability of the same test result when the disease is absent (FP).

Likelihood Ratio of a positive test (LR+)

A convenient graphic tool that uses a logarithmic scale to determine posttest probability, given the LR at a specified cutoff and the pretest probability

FAGAN NOMOGRAM

a useful tool for identifying the optimal cutoff for a diagnostic test by calculating the sensitivity and specificity combinations across the entire range of cut off values

RECEIVER OPERATOR CHARACTERISTIC CURVE

a method that allows one to assess the optimal cutoff with numeric estimates for clinical impact, or consequences, of test results.

POSITIVITY CRITERION

• Is a process by which medical decision can be made by using as many objective tools as possible. • Can help to reduce the uncertainty of medical decision making.

EVIDENCE-BASED MEDICINE

5 Steps of EBM

1. Ask a clinical question based on a patient encounter 2. Acquire information by searching for resources 3. Analyze and critically evaluate the information and reach a conclusion 4. Apply the information to individual patients 5. Audit effectiveness and monitor the literature

The clinical question can be described in four parts with | acronym of PICO

- Problem - Intervention - Comparison - Outcome

Chapter 7: Postanalysis Flashcards

(58 cards)