OBJECTIVE: ANA
- What is it?
- Disease associations?
- How is it measured?
- Patterns
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)
- diffuse - useless
- ** Peripheral** - due to Abs to either sDNA or dsDNA
- dsDNA is specific for SLE
- Speckled - ENA (extractable nuc. abs)
- can be purified out for further testing
- anti-centromere - specific for limitied scleroderma (CREST)
- nucleolar - systemic sclerosis or SLE
ENA is a reflex panel done to follow-up on strongly positive ANA.
OBJECTIVE: RF
- What is it?
- Disease associations?
- How is it measured?
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
OBJECTIVE: Appropriate use of “tests of inflamm” (i.e. ESR and CRP)
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
OBJECTIVE: ACPA vs. RF
ACPA as sensitive and is more specific for RA than RF
RF increases w/ age is elevated by myriad conditions
OBJECTIVE: Review sensitivity and specificity (negative in health, positive in disease, Spin, Snout)
- 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
OBJECTIVE: Concept of seropositivity and seronegativity
.
PPV equation
TP/all positives
NPV
TN/all negatives
Modifiable risk factors that increase the amount of citrullinated proteins.
- smoking
- P. gingivitis
Anti-Sm is specific for
SLE, also good prognostic sign that pt will have milder dz
small nuclear cytoplasmic antibody
Anti-DNA topoisomeraes (Scl-70) is specific for?
Diffuse Cutaneous Systemic Sclerosis
- Worse prognosis than w/ Anti-Centromere
- more renal dz, ILD etc
Anti-tRNA synthase is specific for?
DM/PM
cANCA
Granulomatosis with polyangiitis 90% specific
a.k.a. PR3 ANCA
pANCA
< specific than cANCA
- seen in microscopic polyarteritis, but also many others
- a.k.a. MPO ANCA
Ro Abs and preg
can cross placenta and cause congenital heart block