Clin Lab med and lab methods Flashcards
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?
-insufficient understanding of labs can lead to misinterpretation of results
-inefficient selection could increase healthcare costs
ranges
-reference range = normal range
-can differ by facility based on instrument and reagent used to perform test
-ranges are determined by people without disease and on no medications -> middle 95% is reference range
-some people have a abnormal number that is normal for them!
-regional differences- ex. hmg
-
desirable ranges
-prognosis related ranges
-established by experts
-associated lab results with clinical outcome
-the range that defines certain dx (not certain!)
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
-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
-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
-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 and 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
-indicates the likelihood that positive test result identifies someone with the disease
-(true positive/true positives + false positives) x 100
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- number of existing cases in population
-incidence- number of new cases occurring within a period of time
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
-preanalytical- 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 variables
-age
-gender
-body mass
-preparation
-posture
-sample type
-diff ranges
analytical interferences
-hemolysis -> can cause high K
-bilirubin -> yellow tint
-lipemia -> cloudy serum
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
-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
-rapid strep test
-urine preg test
-mammogram
-PSA
-pap smear
-total cholesterol level
-TSH
-urine tox screen
-monospot
-COVID home test
-COVID PCR
specimens
-turn around time
-tube for collection
-timing
blood cultures
-2 samples from diff parts of body bc of possible contamination
-collected before antibiotics
-aerobic and anaerobic
types of lab samples
-blood (peripheral or central)
-urine
-stool
-mucus/sputum
-wound
-tissue
-CSF
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
-serum = plasma - clotting factors
serum vs plasma
-Clotted blood that is centrifuged to remove the clot and any cells is known as SERUM
-Blood that has not been clotted and is then centrifuged to remove any cells is known as PLASMA
-Testing for blood cell counts and clotting factors
-serum is liquid with clotted blood
-plasma is liquid in spun down tube
cell injury
-Plasma Markers of Organ Damage:
-Injured cells leak components “markers”
-Troponin
-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)
