Principles of Laboratory Medicine Flashcards
Lab tests consume about ___% of annual health care costs in the U.S.
2.3
More than ___% of the objective data in a patient’s medical record comes from the clinical laboratory.
70
What is laboratory medicine?
The medical discipline that specializes in the performance, reporting, and interpretation of clinical laboratory tests in the provision of high quality patient care.
Who is on the laboratory medicine team?
- Pathologists
- Doctoral-level lab scientists
- Technologists
- Technicians
True or false - the specific types of clinical laboratories in health care institutions varies greatly from one place to another.
True
What is a reference lab?
Provide testing services for patients and healthcare providers; labs are generally specialized tests ordered infrequently or that require specialized equipment
What is point of care testing?
Lab testing performed on simpler devices at the point of care and often by non-lab personnel
What is the key objective of POCT?
Producing a result more quickly
What are some examples of POCT?
Urine HCG, glucose testing, INR, troponin
What are the 4 major roles of lab tests in patient care?
- Diagnosis of disease
- Monitoring of disease, therapies, and interventions
- Screening for disease
- Research
True or false - lab tests should be ordered based on clinical questions.
True
What are the negative effects of unnecessary lab tests?
- Increased cost of healthcare
- Contribute to development of iatrogenic anemia
- Unnecessary work-up if there are errors in the diagnostic testing process
Describe the process of lab testing.
- Clinical develops a clinical question.
- Specific lab test is selected
- Test is ordered
- Specimen is collected
- Sample is prepared for analysis
- Sample is analyzed
- Result is verified
- Result is reported
- Test result is interpreted in the context of a clinical scenario
- Action is taken
- Patient care is affected
What are the 3 phases of diagnostic testing?
- Pre-analytic
- Analytic
- Post-analytic
What are the steps of the pre-analytic phase?
- Clinical develops a clinical question.
- Specific lab test is selected
- Test is ordered
- Specimen is collected
What are the steps of the analytic phase?
- Sample is prepared for analysis
- Sample is analyzed
- Result is verified
What are the steps of the post-analytic phase?
- Result is reported
- Test result is interpreted in the context of a clinical scenario
- Action is taken
- Patient care is affected
What are the steps involved in preparation of the patient and collection of a specimen?
- Obtaining appropriate clinical history
- Ordering the right test
- Proper timing and collection of lab specimens
- Correct patient ID
- Correct specimen labeling
- Use of appropriate sample collection containers
- Proper handling and transportation of specimen
- Proper accessioning of specimens
What are the effects of misuse of clinical testing/order wrong/inappropriate tests?
- Delayed decisions
- Prolonged hospital stays
- Missed or delayed diagnoses
- Increased cost
Appropriate ordering and interpretation of lab tests must incorporate the ___.
Clinical scenario
65-75% of all errors in the testing process are from the ___ phase.
Pre-analytical
True or false - time of day, month, or year may affect lab test results.
True
What are some examples of tests that must be collected at specific times or days?
- Blood counts/electrolytes (minimal diurnal variation)
- Hormonal level measurements (day/month)
- Therapeutic drug monitoring is often linked with timing of drug administration
How do cortisol levels fluctuate throughout the day?
Peaks in the early morning, lowest in the late evening around bedtime
How does cortisol vary in patients with Cushing syndrome?
Elevated late night salivary and serum cortisol values
What are other biologic variables that may affect test results?
- Age
- Gender
- Race
- Exercise
- Diet
- Posture
- Genetic predisposition
When should triglyceride level be obtained and why?
In the fasting state, as levels increase with eating; postprandial increase is due to presence of chylomicrons, typically 3-6 hours following a meal
Correct ___ must be used for specimens to ensure the ordered test is performed on the specimen under proper conditions.
Collection tubes
What is a common reason for specimen rejection?
Wrong tube type
Different tube types contain different ___.
Additives
Red cap test tubes have which additives, mode of action, and are used for which tests?
Additive: none
MoA: blood clots and serum is separated by centrifugation
Tests: chemistires, immunology, serology
Lavender cap test tubes have which additives, mode of action, and are used for which tests?
Additive: EDTA
MoA: anticoagulant, removes Ca2+
Tests: CBC, blood bank crossmatch
Light blue cap test tubes have which additives, mode of action, and are used for which tests?
Additive: 3.2% sodium citrate
MoA: anticoagulant, removes Ca2+ (preserves labile pro-coagulants)
Tests: PT, PTT, D-Dimer
Light green cap test tubes have which additives, mode of action, and are used for which tests?
Additive: plasma separating tube with lithium heparin
MoA: heparin anticoagulates, plasma is separated from PST gel at body of tube
Tests: most chemistries
Gold cap test tubes have which additives, mode of action, and are used for which tests?
Additive: none
MoA: Serum separator tube (SST) contains a gel at the bottom to separate blood from serum on centrifugation
Tests: Chemistries, immunology, serology
In addition to wrong tube type, what are other reasons specimens are rejected?
- Mislabeled or unlabeled
- Clotted specimen
- QNS (quantity not sufficient)
Why is a mislabeled/unlabeled specimen a problem?
Patient identity error can lead to reporting of the wrong test result for a patient
How does a clotted specimen develop?
Drawing blood into a syringe and then injecting it into the tube, Overfilling a test tube that has an anti-coagulant
How does QNS occur?
Stopping the blood draw before filling the tube completely
Which phase has the least error in lab testing?
Analytical
Current methods and equipment used to generate test results have a high degree of what two things?
- Accuracy
2. Precision
What is accuracy?
Correctness - how closely the measurement approaches the true value of the analyte
What is precision?
Reproducibility - how closely together are results from measurements of the same substance in the same sample
Why is a precise, inaccurate lab test still accurate?
Trends can indicate issues
Many lab tests are performed on ___ instruments.
Automated
In addition to advances in technology, why are lab tests trending toward automation?
Shortage of allied healthcare personnel entering the field of lab medicine
Despite advances in automated lab techniques, some tests are still performed ___.
Manually
Once an accurate test result is obtained, the lab must do what?
Report the result in a timely manner by using an electronic process allowing for acceptable results to be transmitted via an interface between analyzer and the lab information system (LIS) and then another interface between the LIS and EMR
OR
Transcribing accurately the results to a paper or written medical recrod
What are critical results of tests?
Results that fall significantly outside the normal range, may indicate a life threatening situation, and may require immediate clinical action
What are the current regulations regarding a critical result?
Require the person receiving the report to be asked to read back the results to the lab staff member to ensure correct information was communicated; this must be documented in the medical record
If a test results from a normal healthy patient, how are normal results determined?
Gaussian distribution - central 95% is the normal range (mean +/- 2 STD)
___% of normal healthy patients may fall outside the normal cutoff values.
5
___ is the ability of a test to detect disease.
Sensitivity (proportion of persons with disease in whom the test is positive) - rule out
___ is the ability of a test to detect the absence of disease.
Specificity (proportion of persons without disease in whom the test is negative) - rule in
What determines what level of result is considered normal/abnormal?
Where the lab places the threshold or cut-off on a normal or reference range
