MSK lab medicine Flashcards
Define specificity
ability of a test to correctly identify those WITHOUT disease
A measure of the ‘true negative’ rate
Define sensitivity
ability of a test to correctly identify those WITH disease
a measure of ‘true positives’
What does SPIN stand for
Specific tests, when Positive, rules disease IN
What does SNOUT stand for
Sensitive tests, when Negative, rule diseases OUT
What is accuracy
measure of the closeness to the ‘true’ value
ability of a test to correctly measure what we intend it to measure
what is precision
measure of the reproducibility of the test
measure of the variation in test performance when other conditions are accounted for
What does reference range mean
the normal range (upper and lower limites of a lab test)
what does the reference range do for us
provides context to the lab results
What is a critical value for a test
a lab result that significantly outside the reference range which is a threat to health and requires urgent intervention
Define point of care testing
testing completed at the bedside, often by non-lab professionals and require smaller sample sizes than in-lab testing,
Rapid turnaround and used for real-time medical decision making
(i.e. urine dip, glucose test)
What is APR
Acute phase reactants
inflammatory markers that rise early in the disease process (ESR, CRP and Procalcitonin)
is APR specific or sensitive
sensitive because they can not reliably be used to distinguish between the causes of inflammation
What is CRP
high-sensitivity (more sensitive than ESR) as it rises in 12-24 hours and peaks in 2-3 days.
what level of CRP is highly suggestive of bacterial infection?
> 10mg/dL or >100mg/L
What does ESR stand for
Erythrocyte sedimentation rate
how does ESR trend?
rises in 24-48 hours and falls slowly over days to months to normalize
What does PCT stand for
Procalcitonin
How do PCT and ESR/CRP compare?
PCT is more sensitive and Specific than ESR/CRP
what is PCT specific to?
infectious etiologies not elevated in rheumatologic conditions
what is the trend for PCT?
rises in 3-4 hours, peaks in 6-24 hours
what does PCT monitor?
bacteremia -> sepsis
What are acid-fast bacilli
Mycobacterial species
M. tuberculosis, M. avium, M. bovis, M. Leprae, etc
These are rare joint pathogens on fluid analysis
What are the common fluids that you will analyze?
pleural - thoracenteiss
CSF - lumbar puncture
Synovial - aspiration/arthrocentesis
What information is gathered by a fluid analysis
visual characteristics of the fluid
viscosity
cell count/cytology
protein levels/LDH
Gram stain/culture
and situation specific tests such as crystals, AFB, PCR, synvosure
What are the indications of arthrocentesis
unexplained joint effusion, monoarthrosis, definitive dx of joint infection or gout/pseudogout and symptomatic relief with large effusions
What are the relative contraindications for arthrocentesis
hemarthosis
overlying infection/wound
acute post-operative
immediately prior to or s/p TJA
inexperienced clinician
uncontrolled bleeding disorder
what are the complications associated with arthrocentesis
infection (complete overlying cellulitis/soft tissue)
severe joint pain
large hemarthrosis
damage to articular cartilage
damage to neurovascular structures
What is the native joint workup for arthrocentesis
gram stain and culture
cell count and diff
AFB and fungal cultures
crystals
glucose
+/- Lyme PCR
What is the string test for arthrocentisis
to test the viscosity
positive string test is normal viscosity, low viscosity is negative
what are the special test for lyme disease
it is difficult to reliably culture B. burgodorfi
The gold standard is Serologic testing - ELISA, measures total IgM and IgG
western blot/immunoblot (secondary) - more detailed IgM and IgG testing
How is IgG classified
as a ‘long-term’ antibody and it only tells us someone is OR was infected
what is the gold standard special test for Lyme arthritis
Lyme PCR
What is the gold standard for diagnosing crystal arthropathies
presence of crystals synovial fluid analysis
what type of crystals does gout present with
needle - monosodium urate
what type of crystals does pseudogout present with
rhomboid square, rods - calcium pyrophosphate
what serum test are available for diagnosing crystal arthropathies in pseudogout
no serum test for psuedogout
how does the imaging decipher between gout and psuedogout
pseudogout presents with chondrocalcinosis and gout has a rat-bit appearacne and tophi
