Concepts in Laboratory Medicine Flashcards
Why do we need labs
Why do we need labs
-60-70% of decision making in med is done based on results of lab tests*
-aid in early dx of disease that may not have clinical presentation
-monitoring progress of disease
why not labs?
why not labs?
-insufficient understanding of labs can lead to misinterpretation of results
-inefficient selection could increase healthcare costs
reference range
-Normal range -can differ by facility
- Determined by individuals without disease on no meds
-Middle 95% is reference range
-some people have a abnormal number that is normal for them!
-regional differences- ex. hmg
desirable ranges
desirable ranges
-prognosis related ranges
-established by experts
-associated lab results with clinical outcome
-the range that defines certain dx (not certain!)
–
therapeutic ranges
therapeutic ranges
-used to monitor medication effects
-window for levels
-below -> is typically inadequate level of medication
-above -> toxic effect level of mediation
-not always drug level -> can be effect produced
–
threshold
Has no range, presence of disease above a level
-ex. troponin, drugs
-once you hit upper limit of normal = confirmation the event is happening -> positive result!
-threshold separates neg and pos results
–
sensitivity
sensitivity
-identifying population with disease
-capacity to identify all individuals with disease
-however as threshold if lowered to capture all with disease -> false positives can rise
-reliability
-99% sensitivity- if person has condition test will pick it up 99% of time
-(true positives / true positives + false negatives) x 100
-you get more false positives when you increase sensitivity*** -> lowering the bar to capture all the positives but you start including false positives
–
specificity
specificity
-focus on population without disease
-correctly identify those without disease
-as threshold raised to capture all those without disease -> false negatives can rise
-(true negative/true negatives + false positives) x 100
-you get more false negatives when you increase specificity*
–
appropriate value
Established to minimize total number of false positives + false negatives**
-HIV- max sensitivity (blood donor) -> this needs to be sensitive bc you need to know if someone has HIV
-pancreatic cancer- max specificity (before treatment) -> you dont want to treat someone if they dont have it
positive predictive value
positive predictive value
-indicates the likelihood that positive test result identifies someone with the disease
The proportion of positive test results that are true positives (i.e., the probability that subjects with a positive screening test truly have the disease).
ex:
100 people tested positive for the disease.
Of those 100, 80 actually have the disease (True Positives)
20 = false positive
80/(80+ 20) = 0.8
negative predictive value
negative predictive value
-indicates the likelihood that a neg test result identifies someone without disease
-(true negatives/true negatives + false negatives) x 100
–
prevalence vs incidence
prevalence vs incidence
-prevalence- number of existing cases in population
-incidence- number of new cases occurring within a period of time
–
precision vs accuracy
precision vs accuracy
-precision- ability to test 1 sample and repeatedly obtain close results - not necessarily the correct but consistent
-accuracy- relationship between number obtained and true result -> correct
-precision and accuracy- consistent and correct
–
phases of lab analysis
phases of lab analysis
-preanalytical (MC error)- any actions or factors involved in acquiring, handling, transporting, and processing a pt specimen prior to actual analysis
-analytical- all factors related to test platform and to testing process itself
-post analytical- interpretation of the test results in light of our expertise as physicians to formulate a dx (or diff dx) to guide pt management
-errors can happen at every phase
–
preanalytical errors
Inappropriate prep of patient
Not fasting, ingesting drugs that interfere, wrong tube, delayed transport of specimen, stored at wrong temp, inadequate amt of blood
What are types of Analytical errors?
Incorrect use of instrumentation or expired reagents
What are types of Post Analytical errors?
reporting results to wrong patient, delayed in time to enter completed results
preanalytical variables
-Age
-Gender: Testosterone and estradiol hormones
-Body mass- muscle mass, creatine kinase, serum cholesterol w obesity +body fat
-Prepping patient for lab testing - fasting
-Patient posture for blood collection :lower plasma when pt is upright,
but… when supine theres fluid movement into circulation, extra volume in circulation can dilute certain compounds in blood
- Samples of venous arterial and capillary- diff concs than eachother
What are 3 major analytical interferences in lab testing?
-hemolysis -> can cause high K
-bilirubin -> yellow tint
-lipemia -> cloudy serum
–
drug impact
drug impact
-you must know if people are on drugs
-ex. coagulation study with pt on thinners
-interfering with test
-producing effect on body
–
selecting a test
selecting a test
-screening before advanced…$$$
-test with reflex
-dont order too many -> remember 5% fall out of normal range
-abnormal results lead to more tests
–
examples of screening tests
examples of screening tests
-rapid strep test
-urine preg test
-mammogram
-PSA
-pap smear
-total cholesterol level
-TSH
-urine tox screen
-monospot
-COVID home test
-COVID PCR
–
specimens
specimens
-turn around time
-tube for collection
-timing
–
blood cultures
-collect 2 samples from diff parts of body bc of possible contamination
-collected before antibiotics
-do one aerobic culture and one anaerobic
–
types of lab samples
types of lab samples
-blood (peripheral or central)
-urine
-stool
-mucus/sputum
-wound
-tissue
-CSF
–
prior to obtaining sample
prior to obtaining sample
-pt appropriately identified
-specimen container labeled
-source of quantity must be determined
-verify prior preparation (fasting)
–
blood samples
-capillary -> heel (newborn) , point of care diabetic testing
-venous -> whole blood, plasma, serum
-arterial
Blood that has NOT been clotted and is then centrifuged to remove any cells is known as
PLASMA
-plasma is liquid in spun down tube
-Testing for blood cell counts and clotting factors
CLOTTED blood that is centrifuged to remove the clot and any cells is known as
SERUM
- serum is the liquid that remains after the blood was clotted AND the clot was removed -> it has NO CLOTTING FACTORS OR FIBRINOGEN
“think serum + skincare -> its smoother and has no clotting factors because you dont want to clog your pores when you put it on”
cell injury
Plasma Markers of Organ Damage:
-Injured cells leak components “markers”
-Troponin:organ damage
-ALT / AST
-not always present -> only shows up when organs are “screaming”
Acute phase reactants:
-Plasma protein changes with inflammation
-ESR, fibrinogen, c-reactive protein, etc
Infections:
-Identify antibody.
-IgM (acute), IgG (Lymes Disease)
–
