Intro to Clinical Lab Flashcards
What are the 16 steps from the decision to order the test to the clinical response to results?
- Order is written/entered into computer
- Lab receives the order
- Phlebotomist goes to draw blood
- Pt is identified
- Phlebotomy
- Blood drawn into appropriate tubes
- Tubes labeled at bedside
- Specimens transported to lab
- Specimens received and processed
- Routed to appropriate section and tests run
- In-lab reports generated
- Results reviewed by technologist
- Computer reports released
- Critical levels are called to doc or nurse (and rechecked)
- Data interpreted
- Clinical response
Describe the contents and use of each of these colored tubes
Red
Red/gray
Light blue
Purple
Green
Gray
Red: serology/chemistry tests
Glass - nothing
Plastic - clot activator
Red/Gray: chemistry tests/serology
clot activator and gel for separating cells/serum
Light blue: coagulation tests
citrate anticoagulant
Purple: CBC/ammonia
EDTA coagulant
Green: blood gases/chemistry tests
heparin anticoagulant
Gray: glucose
fluoride with oral ate anticoagulant
Describe the laboratory testing cycle and what is involved in the pre-analytic phase, analytic phase, post-analytic phase.
Decision to perform test
Pre-analytic Phase:
- Order placed
- Order transferred to lab
- Identifying information entered
- Specimen
Analytic Phase:
Specimen analyzed
Post-analytic Phase:
- Report generated
- Result conveyed to clinician
- Data interpreted
- Clinical response to result
Where do the majority of laboratory errors occur?
Mostly during pre-analytical phase
What are the 3 categories of pre-analytical variables?
What are ways to minimize these variables?
- Sample collection
- Sample handling
- Patient factors
Minimizing variables:
- physicians writing legibly, entering carefully, or civilly asking for clarification
- ordering tests at appropriate times
What are 2 analytical variables?
- Interfering substances
- Instrument/reagent issues
What are 3 post-analytical variables?
What are ways to minimize post-analytical variables?
- Interpretation/misinterpretation of the results
- Physician did not receive report or did not look at it
- Data transfer errors in medical record
Minimizing variables
- compare current results to previous
- be accurate in data transfer in the chart
- NEVER ACT ON LAB RESULTS THAT DON’T FIT THE CLINICAL PICTURE (recheck recheck recheck)
- don’t order a test if you don’t know what to do with results
- always follow up on tests
- don’t “shotgun”
What are the two steps of the post-analytic lab result review? Who performs this?
- Analytic correctness - done by technologist before results are released
- Clinical significance - done by physician after receiving results
What is a reference interval and how is this determined?
Reference intervals (normal ranges) - the range at which 95% of people without disease fall
Define the following terms in words and equations.
Sensitivity
Specificity
What are these used for and why?
Sensitivity = TP/(TP + FN)
- The probability of a positive result in a sick person
- Used to rule out disease - very important false negatives are low when screening, better to have a false positive and continue work up
Specificity = TN/(TN + FP)
- The probability of a negative result in a not sick person
- Used to confirm disease - more important at this point to avoid false positives, while a false negative is not as important
Define the following in equations and words.
Positive predictive value
Negative predictive value
Positive predictive value (PPV) = TP/(TP+FP)
- the probability that someone with a positive test is sick
Negative predictive value (NPV) = TN/(TN+FN)
- the probability someone with a negative test isn’t sick
Define prevalence and incidence.
Prevalence - number of existing cases in a population (expressed as a percentage) at a given time
Incidence - number of new cases in a population per unit of time
Would screening tests require a high sensitivity or specificity?
What about confirmatory tests?
Screening tests:
- Rule out - avoid false negatives, false positives are fine so you can cast a wide net
- Sensitivity (TP/TP+FN): high sensitivity means likely that a diseased patient will test positive
Confirmatory tests:
- Rule in - avoid false positives so at the end of the process you do not want to confirm the pt has a disease that they don’t
- Specificity (TN/TN+FP): high specificity means likely that a person without disease tests negative
