02-28 Laboratory Testing in Rheumatology Flashcards Preview

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Flashcards in 02-28 Laboratory Testing in Rheumatology Deck (15)
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1
Q

OBJECTIVE: ANA

  • What is it?
  • Disease associations?
  • How is it measured?
  • Patterns
A

Antibodies against one of many nuclear proteins

Disease Associations

  • SLE - 98% sensitive
    • but highly non-specific

How It Is Measured

  • old: look for LE cell
  • IIF: HEp2 or rodent cells
  • ELISA/EIA (enzyme immunoassay): automated, lower personnel costs

Five Patterns (see cocktail glass)

  1. diffuse - useless
  2. ** Peripheral** - due to Abs to either sDNA or dsDNA
    • dsDNA is specific for SLE
  3. Speckled - ENA (extractable nuc. abs)
    • can be purified out for further testing
  4. anti-centromere - specific for limitied scleroderma (CREST)
  5. nucleolar - systemic sclerosis or SLE

ENA is a reflex panel done to follow-up on strongly positive ANA.

2
Q

OBJECTIVE: RF

  • What is it?
  • Disease associations?
  • How is it measured?
A

It’s an IgM against Fc region of other Igs

Associate with everything under the sun

Measured by agglutination to latex particles coated w/ human IgG

  • 1:80 is positive cut-off
  • also get
3
Q

OBJECTIVE: Appropriate use of “tests of inflamm” (i.e. ESR and CRP)

A

ESR

  • Normal values based on age & sex
    • ♂ upper limit of normal is age/2
    • ♀ (age + 10)/2
  • seriously high if > 100; DDx
    • Malignancy
    • Inflammatory rheumatic disease
    • Infection
    • Renal disease
    • Less than 5% will have no explained cause
  • Used to monitor RA, vasculitis, etc.

CRP

  • If wicked high and ESR equivocal, think infection
  • Named for reactivity to pneumococcal c-polysaccharide
  • More expensive to get than ESR
4
Q

OBJECTIVE: ACPA vs. RF

A

ACPA as sensitive and is more specific for RA than RF

RF increases w/ age is elevated by myriad conditions

5
Q

OBJECTIVE: Review sensitivity and specificity (negative in health, positive in disease, Spin, Snout)

A
  • Sensitivity => PID (positive in disease)
  • Specificity => NIH (negative in health)
  • S(P)in: when a specific test is positive you rule in a disease
  • S(N)out: when a sensitive test is negative you rule out a dz
6
Q

OBJECTIVE: Concept of seropositivity and seronegativity

A

.

7
Q

PPV equation

A

TP/all positives

8
Q

NPV

A

TN/all negatives

9
Q

Modifiable risk factors that increase the amount of citrullinated proteins.

A
  • smoking
  • P. gingivitis
10
Q

Anti-Sm is specific for

A

SLE, also good prognostic sign that pt will have milder dz

small nuclear cytoplasmic antibody

11
Q

Anti-DNA topoisomeraes (Scl-70) is specific for?

A

Diffuse Cutaneous Systemic Sclerosis

  • Worse prognosis than w/ Anti-Centromere
  • more renal dz, ILD etc
12
Q

Anti-tRNA synthase is specific for?

A

DM/PM

13
Q

cANCA

A

Granulomatosis with polyangiitis 90% specific

a.k.a. PR3 ANCA

14
Q

pANCA

A

< specific than cANCA

  • seen in microscopic polyarteritis, but also many others
  • a.k.a. MPO ANCA
15
Q

Ro Abs and preg

A

can cross placenta and cause congenital heart block