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44 Cards in this Set
- Front
- Back
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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) |
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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) |
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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 |
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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? |
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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 |
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Accuracy
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-does the test give you the correct answer
-does it measure what it is supposed to measure |
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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 |
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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 |
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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 |
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Sensitivity
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-ability of a test to detect patient with a specific disease
-amount of false negatives results |
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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 |
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True Positives
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-test says positive
-real answer is positive |
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False Positives
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-test says positive
-real answer is negative |
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True Negatives
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-test says negative
-real asnwer is negative |
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False negatives
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-test says negative
-real answer is positive |
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Sensitivity calculation
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TP/ (TP + FN) x 100
ability of test to detect a (+) result |
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Specificity calculation
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TN/ (TN + FP) x 100
ability of the test to be correct about + result |
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Prevalence
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-how often the condition occurs in nature
can influence the predictive value |
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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 |
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Predictive Value Calculation
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TP/ (TP + FP) x 100
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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 |
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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 |
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Screening tool for colon cancer
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-high sensitivity
-low specificity -low cost -innocuous |
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Mammogram for Breast Cancer
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-moderate to low sensitivity
-high specificity -moderate cost |
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Brain Biopsy screening tool for tumor
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-high specificity
-low sensitivity -high cost -not very innocuous |
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Three cateogories for laboratory errors
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1. pre-analytical
2. analytical 3. post-analytical |
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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 |
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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 |
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Preanalytical Errors in improper pt preparation
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-collection site not prepared
-fasting state -medications -exercise -time of day |
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Preanalytical Errors in Environmental Factors
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-sample got hot/cold
-sample was shaken -sample was exposed to light |
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Preanalytical Errors in Timing
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-different tests need to by run within different time periods
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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 |
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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 |
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Sources of analytic error include:
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-test to test carry over
-improper processing -interfering substances -instrument failure |
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Post-analytical error
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-results are released to clinician
-clinician interprets results -clinician makes diagnostic or therapeutic deceisions |
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STAT
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-means now
-lab drops it routine work-laod to comply -generally available eithin 1 hour of request |
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ASAP
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-next available run or when tech is available
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Routine
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-will be done when most efficient
-usually within 24 hours |
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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 |
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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 |
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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 |
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CLIA categorized lab test
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-waived
-PPM (provider-performed microscopy procedures) -moderate complexity -high complexity |
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PPM
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-performed by physician, mid-level practitioner, dentist
-moderately complex procedure -primary instrument is microscope -limited specimen handling required |
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PPM includes:
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-wet preps and KOH
-pinworm exam -urine sediment exam |
