MSK lab medicine Flashcards

1
Q

Define specificity

A

ability of a test to correctly identify those WITHOUT disease

A measure of the ‘true negative’ rate

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2
Q

Define sensitivity

A

ability of a test to correctly identify those WITH disease

a measure of ‘true positives’

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3
Q

What does SPIN stand for

A

Specific tests, when Positive, rules disease IN

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4
Q

What does SNOUT stand for

A

Sensitive tests, when Negative, rule diseases OUT

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5
Q

What is accuracy

A

measure of the closeness to the ‘true’ value

ability of a test to correctly measure what we intend it to measure

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6
Q

what is precision

A

measure of the reproducibility of the test

measure of the variation in test performance when other conditions are accounted for

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7
Q

What does reference range mean

A

the normal range (upper and lower limites of a lab test)

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8
Q

what does the reference range do for us

A

provides context to the lab results

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9
Q

What is a critical value for a test

A

a lab result that significantly outside the reference range which is a threat to health and requires urgent intervention

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10
Q

Define point of care testing

A

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)

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11
Q

What is APR

A

Acute phase reactants

inflammatory markers that rise early in the disease process (ESR, CRP and Procalcitonin)

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12
Q

is APR specific or sensitive

A

sensitive because they can not reliably be used to distinguish between the causes of inflammation

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13
Q

What is CRP

A

high-sensitivity (more sensitive than ESR) as it rises in 12-24 hours and peaks in 2-3 days.

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14
Q

what level of CRP is highly suggestive of bacterial infection?

A

> 10mg/dL or >100mg/L

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15
Q

What does ESR stand for

A

Erythrocyte sedimentation rate

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16
Q

how does ESR trend?

A

rises in 24-48 hours and falls slowly over days to months to normalize

17
Q

What does PCT stand for

A

Procalcitonin

18
Q

How do PCT and ESR/CRP compare?

A

PCT is more sensitive and Specific than ESR/CRP

19
Q

what is PCT specific to?

A

infectious etiologies not elevated in rheumatologic conditions

20
Q

what is the trend for PCT?

A

rises in 3-4 hours, peaks in 6-24 hours

21
Q

what does PCT monitor?

A

bacteremia -> sepsis

22
Q

What are acid-fast bacilli

A

Mycobacterial species
M. tuberculosis, M. avium, M. bovis, M. Leprae, etc

These are rare joint pathogens on fluid analysis

23
Q

What are the common fluids that you will analyze?

A

pleural - thoracenteiss
CSF - lumbar puncture
Synovial - aspiration/arthrocentesis

24
Q

What information is gathered by a fluid analysis

A

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

25
Q

What are the indications of arthrocentesis

A

unexplained joint effusion, monoarthrosis, definitive dx of joint infection or gout/pseudogout and symptomatic relief with large effusions

26
Q

What are the relative contraindications for arthrocentesis

A

hemarthosis
overlying infection/wound
acute post-operative
immediately prior to or s/p TJA
inexperienced clinician
uncontrolled bleeding disorder

27
Q

what are the complications associated with arthrocentesis

A

infection (complete overlying cellulitis/soft tissue)
severe joint pain
large hemarthrosis
damage to articular cartilage
damage to neurovascular structures

28
Q

What is the native joint workup for arthrocentesis

A

gram stain and culture
cell count and diff
AFB and fungal cultures
crystals
glucose
+/- Lyme PCR

29
Q

What is the string test for arthrocentisis

A

to test the viscosity
positive string test is normal viscosity, low viscosity is negative

30
Q

what are the special test for lyme disease

A

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

31
Q

How is IgG classified

A

as a ‘long-term’ antibody and it only tells us someone is OR was infected

32
Q

what is the gold standard special test for Lyme arthritis

A

Lyme PCR

33
Q

What is the gold standard for diagnosing crystal arthropathies

A

presence of crystals synovial fluid analysis

34
Q

what type of crystals does gout present with

A

needle - monosodium urate

35
Q

what type of crystals does pseudogout present with

A

rhomboid square, rods - calcium pyrophosphate

36
Q

what serum test are available for diagnosing crystal arthropathies in pseudogout

A

no serum test for psuedogout

37
Q

how does the imaging decipher between gout and psuedogout

A

pseudogout presents with chondrocalcinosis and gout has a rat-bit appearacne and tophi