Clinical Lab: Intro
Terms
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- Benefits of Diagnostic Tests
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-disease screening (identify risk factors)
-diagnosis
-patient management (severity of dz, prognosis, monitor disease progress) - Negative Side of Laboratory Tests
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-cost
-managed care pre-approval/justification
-invasive/painful
-morbidity/mortality associated with tests (false positive or false negatives)
-laboratory inequalities
-time factors (minutes to days) - Cost of health care
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-over 1.3 trillion spent on health care in U.S.
-lab tests comprise approx 10% ot total health care costs - Pre-ordering quetions
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-how will the test help you?
-why are you ordering the test?
-will the test results change your plans?
-what do you hope to gain from the test?
-so the risks of testing outweight the benefits of the test results?
-how soon do you need the inoformation? - What makes a test clinically useful?
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-methodology is well described and clinical useful
-test is accurate and precise
-test has well established reference ranges
-test is sensitive and specific - Accuracy
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-does the test give you the correct answer
-does it measure what it is supposed to measure - Sources of inaccuracy
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-Human error (obtaining the sample, performance of the test, transciption of the results, interpretation of the results)
-wrong patient
-broken equipment - Precision
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-to what detail can the test detect differences
-e.g. measuring the height of a tree
56 steps
20.5 yards
62 feet 3 inches
62 feet 3.247638349 inches - Reproducability
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-likelihood that you will get the same result next time you do the test
-results usually fall within a Gaussian distribution (bell curve)
-normal range is +/- 2 standard deviations (95%)
-the more precise a test, the more evident the error - Sensitivity
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-ability of a test to detect patient with a specific disease
-amount of false negatives results - Specificity
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-ability to detect only the analyte of interest
-how well test abnormality is restricted to those with the disease in question
-amount of false positive results - True Positives
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-test says positive
-real answer is positive - False Positives
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-test says positive
-real answer is negative - True Negatives
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-test says negative
-real asnwer is negative - False negatives
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-test says negative
-real answer is positive - Sensitivity calculation
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TP/ (TP + FN) x 100
ability of test to detect a (+) result - Specificity calculation
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TN/ (TN + FP) x 100
ability of the test to be correct about + result - Prevalence
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-how often the condition occurs in nature
can influence the predictive value - Predictive Value
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-smaller the number of cases of the disease in the population, the more likely the (+) test result will be a false positive
-the more common the disease in the population, the more likely that the (+) result is true - Predictive Value Calculation
- TP/ (TP + FP) x 100
- Reference Ranges
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-normal population has lab values which fall within a gaussian distribution
-95% of the group lie within 2 standard deviation
-many ranges are age dependent
-normal range may very between labs - Screening Tests should be..
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-sensitive
-sepcific
-inexpensive
-innocuous
-high prevalance of disease in population
-signigicant morbidity and mortality
-effective tx available
-improved outcome if early intervention - Screening tool for colon cancer
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-high sensitivity
-low specificity
-low cost
-innocuous - Mammogram for Breast Cancer
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-moderate to low sensitivity
-high specificity
-moderate cost - Brain Biopsy screening tool for tumor
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-high specificity
-low sensitivity
-high cost
-not very innocuous - Three cateogories for laboratory errors
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1. pre-analytical
2. analytical
3. post-analytical - Pre-analytical Errors occurs:
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-at time of pt assessment
-test order entry
-request completion
-communication to lab
-specimen collection
-specimen transoport
-specimen receipt in lab - Preanalytical Errors in specimen collection
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-sample too small
-sample contominated
-sample lost
-sample mixed up with others
-sample mis-labeled
-sample collected in wrong tube - Preanalytical Errors in improper pt preparation
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-collection site not prepared
-fasting state
-medications
-exercise
-time of day - Preanalytical Errors in Environmental Factors
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-sample got hot/cold
-sample was shaken
-sample was exposed to light - Preanalytical Errors in Timing
- -different tests need to by run within different time periods
- Preanalytical error: Common conditions that effect lab results
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-IV fluids running at time of collection
-effect of dehydration
-effect of heparin flushes (sample collected from ports or IV lines)
-administration od meds at unexpected times
-poor communication between provider and nurses - Analytical phase beginning and end
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-begins when specimen is prepped for testing
-ends when result is interpreted and results are verified and ready to report - Sources of analytic error include:
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-test to test carry over
-improper processing
-interfering substances
-instrument failure - Post-analytical error
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-results are released to clinician
-clinician interprets results
-clinician makes diagnostic or therapeutic deceisions - STAT
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-means now
-lab drops it routine work-laod to comply
-generally available eithin 1 hour of request - ASAP
- -next available run or when tech is available
- Routine
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-will be done when most efficient
-usually within 24 hours - Ancillary Testing: point of care
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-no central clinical lab on site but some tests can be done in the oddice or on pt floor by trained persons
-CLIA waived test - Examples of ancillary testing
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-fingerstick glucose
-urine dipstick
-fecal occult blood
-pregnancy testing
-micro-albumin
-spun hematocrit
-ovulation test
-ESR
-hemoglobin
-Physician performed microscopy - CLIA
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-Clinical Laboratory Improvement Amendments of 1988
-set standards to improve quality in all laboratory services
-US department of health and human services - CLIA categorized lab test
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-waived
-PPM (provider-performed microscopy procedures)
-moderate complexity
-high complexity - PPM
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-performed by physician, mid-level practitioner, dentist
-moderately complex procedure
-primary instrument is microscope
-limited specimen handling required - PPM includes:
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-wet preps and KOH
-pinworm exam
-urine sediment exam