Rheumatoid factor
One of the most used & abused tests in #rheumatology
Let's learn a bit about its origin & utility!
#MedEd #MedTwitter #RheumTwitter
(1/15)
One of the most used & abused tests in #rheumatology
Let's learn a bit about its origin & utility!
#MedEd #MedTwitter #RheumTwitter
(1/15)
1️⃣ what is RF actually?🤷♀️
They are antibodies directed against the Fc fragment of IgG antibody
(2/15)
They are antibodies directed against the Fc fragment of IgG antibody
(2/15)
2️⃣ How & when was it first discovered?📆
1st described by Waaler in 1940, a factor present in 🚶♂️serum (in patients with RA & other diseases) that agglutinates 🐑 RBCs when sensitised with sub agglutinating doses of anti-🐑-RBC 🐰 immunoglobulin
onlinelibrary.wiley.com
(3/15)
1st described by Waaler in 1940, a factor present in 🚶♂️serum (in patients with RA & other diseases) that agglutinates 🐑 RBCs when sensitised with sub agglutinating doses of anti-🐑-RBC 🐰 immunoglobulin
onlinelibrary.wiley.com
(3/15)
The most active sera were from patients with RA, however, only 50 of 77 RA patients had a positive RF!
Hence he concluded ⏬
(4/15)
Hence he concluded ⏬
(4/15)
🌹 Rose further described in 1948 that high titres were found in patients suffering from active RA compared to those with rheumatic fever & other arthritis
Since it was first discovered in patients with RA, it was named as 'Rheumatoid Factor'
pubmed.ncbi.nlm.nih.gov
(5/15)
Since it was first discovered in patients with RA, it was named as 'Rheumatoid Factor'
pubmed.ncbi.nlm.nih.gov
(5/15)
The rose waaler test is now obsolete as we obviously don't want to deal with 🐑 & 🐰 now!
3️⃣ So, what methods are used to detect RF now?
(6/15)
3️⃣ So, what methods are used to detect RF now?
(6/15)
🔹Latex agglutination
Replace RBCs➡️ latex particles!
✅ Simple
✅ Inexpensive
✅ Semiquantitative
✅ Sensitive
❎ Low throughput
❎ Semiquantitative
❎ Isotyping can't be done
To note, exact titre estimation & isotyping are not of relevance in the clinic!
(7/15)
Replace RBCs➡️ latex particles!
✅ Simple
✅ Inexpensive
✅ Semiquantitative
✅ Sensitive
❎ Low throughput
❎ Semiquantitative
❎ Isotyping can't be done
To note, exact titre estimation & isotyping are not of relevance in the clinic!
(7/15)
🔹ELISA
🔹Nephelometry
🔹Turbidiometry
✅ Sensitive
✅ High throughput
✅Automated
✅ Quantitative
✅ Isotyping (ELISA)
❎ Expensive
(8/15)
🔹Nephelometry
🔹Turbidiometry
✅ Sensitive
✅ High throughput
✅Automated
✅ Quantitative
✅ Isotyping (ELISA)
❎ Expensive
(8/15)
4️⃣ does a positive RF= RA?
❗NO❗
RF is non specific & can be present in numerous other diseases.
Top off the list being
🔹Infections
🔹Other autoimmune diseases
🔹Chronic diseases
🔹Malignancies
🔹Even healthy individuals!
hindawi.com
(9/15)
❗NO❗
RF is non specific & can be present in numerous other diseases.
Top off the list being
🔹Infections
🔹Other autoimmune diseases
🔹Chronic diseases
🔹Malignancies
🔹Even healthy individuals!
hindawi.com
(9/15)
To note, a very high prevalence of RF is observed in
🔹Sjogren
🔹Hepatitis C
🔹PBC
🔹Type II cryoglobulinemia
(10/15)
🔹Sjogren
🔹Hepatitis C
🔹PBC
🔹Type II cryoglobulinemia
(10/15)
5️⃣ what about the converse? Does a negative RF rule out RA?
Again, ❗NO❗
The sensitivity of RF for RA is 60-90%, so patients with RA can be negative for RF
(11/15)
Again, ❗NO❗
The sensitivity of RF for RA is 60-90%, so patients with RA can be negative for RF
(11/15)
6️⃣ Does seropositive & seronegative RA differ?
Yes in some aspects.
RF positivity is associated with a severe erosive disease & extra articular manifestations
(12/15)
Yes in some aspects.
RF positivity is associated with a severe erosive disease & extra articular manifestations
(12/15)
7️⃣ is there a role of repeat RF testing during treatment ?
Please, ❗NO❗
RF may decline or turn negative with the use of Rituximab or TNFis but this decline has no clinical utility
(13/15)
Please, ❗NO❗
RF may decline or turn negative with the use of Rituximab or TNFis but this decline has no clinical utility
(13/15)
8️⃣ what about IgA and IgG RF?
The majority of seropositive patients have IgM RF (>90%) & hence most commonly detected
pubmed.ncbi.nlm.nih.gov
IgA>IgG RF are associated with
🔹Greater specificity for future development of RA in preclinical cases
🔹More severe disease
(14/15)
The majority of seropositive patients have IgM RF (>90%) & hence most commonly detected
pubmed.ncbi.nlm.nih.gov
IgA>IgG RF are associated with
🔹Greater specificity for future development of RA in preclinical cases
🔹More severe disease
(14/15)
🔺BUT🔺
Isolated IgA/IgG RF positivity is highly uncommon.
Again, anti-CCP is an easily available specific assay for patients negative for IgM RF.
Hence the clinical utility of RF isotyping is minimal.
(15/15)
#MedTwitter
Isolated IgA/IgG RF positivity is highly uncommon.
Again, anti-CCP is an easily available specific assay for patients negative for IgM RF.
Hence the clinical utility of RF isotyping is minimal.
(15/15)
#MedTwitter
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