Intro to Lab Medicine & Common Lab Tests Flashcards
Define reference range
range of values within a population of people who do not have a given disease
- upper and lower limits
- can vary from lab to lab
- usually central 95%
Define desirable range
prognosis related ranges
associate lab results with clinical outcomes - can be a goal rather than a normal result
Define therapeutic range
can measure effectiveness of a medication or
screen for possible toxicity
Define laboratory threshold
a value that is set to catch presence of disease above a threshold, can result in false positives or false negatives
Sensitivity focuses on a population of individuals who ____ the disease
have the disease
Define sensitivity
capacity to identify individuals with the disease
Sensitive tests have ____ diagnostic thresholds and specific tests have ____ diagnostic thresholds
low (more false positives), high (more false negatives)
Define specificity
how effective a test is at correctly identifying people without disease
Specificity focuses on a population of individuals who _____ the disease
don’t have the disease
Positive predictive value focuses on people with a _____ test result, negative predictive value focuses on people with a ____ test result
positive, negative
Positive predictive value predicts the likelihood that…
a positive test identifies someone with the disease (TB test in community with high prevalence)
Negative predictive value predicts the likelihood that…
a negative test result identifies someone without the disease (D-dimer)
Define prevalence
number of existing cases in a population (expressed as a percent)
Define incidence
number of new cases occurring within a period of time (expressed as a number per year)
Reasons for ordering a test
- diagnosing a disease
- monitoring a disease/interventions
- screening for a disease
- research
Questions to ask before ordering a test
- why is it being ordered
- what are the consequences of not ordering
- how sensitive/specific is the test
- how are the results interpreted
- how will the test results influence patient management
3 phases of the lab testing cycle
pre-analytic
analytic
post-analytic
When do most errors occur within lab testing
in the pre-analytic phase
Define the rifle approach
ordering specific tests based on diagnostic accuracy and predictive value
Define the shotgun approach
indiscriminately ordering a large number of tests
What does a pale yellow to amber color urine specimen mean?
Normal
What does a straw color urine specimen mean?
normal but low specific gravity (hydrated)
What does an amber color urine specimen mean?
normal but high specific gravity (dehydrated)
What can colorless urine mean?
- large fluid intake
- diabetes mellitus
- diabetes insipidus
What can turn urine orange?
Pyridium/AZO
What can turn urine reddish or dark brown?
- blood (RBCs)
- hemoglobin
- myoglobin
What does high specific gravity mean
dehydration
what does low specific gravity mean?
hydrated (also diabetes insipidus)
Low pH means
acidic
High pH means
basic
Acidic urine can mean…
uncontrolled DM - ketoacidosis
alkaline urine can mean…
UTI (bacteria strains sometimes)
Hematuria means
blood in the urine
Common/Important clinical implications of hematuria
- lower UTI
- nephrolithiasis
- urinary tract cancers
- renal cancers
- urinary catheter
- anticoagulants
- strenuous exercise
Clinical implications of proteinuria
kidney diseases
Proteinuria means
protein in the urine (mild, moderate, severe)
The presence of _____ in the urine is the single most important indication of renal disease, even in an apparently healthy person if persistent
protein
Term for increased urinary glucose is
glucosuria or glycosuria
increased glucosuria can mean someone has…
diabetes mellitus
Positive urine glucose requires evaluation for which disease
diabetes
ketonuria
term for increased urinary ketones
clinical implications of ketonuria
- diabetes mellitus (ketoacidosis)
- starvation/fasting
False positive for urinary ketones can be caused by
dehydration and medications
Urine nitrite is a marker for _____
bacteria
One interfering factor for urine nitrite is
pyridium/AZO (false positive)
Clinical implications of urine leukocyte esterase presence is
UTI
False positive for urine leukocyte esterase can be cased by
vaginal discharge, infections, contamination
False negative for leukocyte esterase can be caused by
pyridium/azo
Increased levels of urinary bilirubin involve this organ
the liver
Increased urobilinogen has clinical implications for ____ and _____
hemolysis and liver disease
What is the timeframe for urine testing
one hour unless refrigerated
What does the presence of casts in urine microscopy indicate?
kidney issues
Bacteria in the urine resemble this food item
sprinkles
WBCs in the urine resemble this food item
cookies
increased WBCs in the urine can be caused by ____, ____, _____, and _____
UTI, stones, cancer, inflammation
RBCs in the urine resemble this food item
donuts
clinical implications of RBCs in the urine are
UTI, renal cancer, bladder cancer, kidney stones
presence of squamous epithelial cells in the urine indicate
contamination of the sample
RBC casts indicate_____
hemorrhage and are always pathologic
- glomerulonephritis