RF (IU/mL) = S × D Where S = Sensitivity of the reagent, i.e. 10 IU/ mL. D = Highest dilution of serum showing agglutination.

 

In rheumatoid arthritis, diagnostically useful

autoantibodies termed as “Rheumatoid factors (RF) can be

detected which are immunoglobulins of the classes IgM,

IgG, IgA and IgE. Practically, IgM class RF with specificity

to human IgG (Fc) is the most useful prognostic marker of

RF. The clinical significance of RF determinations consists

in differentiation between rheumatoid arthritis, in which

RFs of modified IgM class have been demonstrated in the

serum of approximately 80% of the cases examined and

rheumatic fever, in which RFs are almost always absent.

The agglutination test is most frequently used because of its

greater sensitivity and simplicity. The RHELAX RF is a latex

agglutination slide test for detection of rheumatoid factors

of the IgM class.

Reagent

1. RHELAX RF reagent: A uniform suspension of

polystyrene latex particles coated with suitably

modified Fc fraction of IgG. The reagent is standardised

to detect 10 IU/mL of RF or more.

2. Positive control, reactive with the RHELAX RF reagent.

3. Negative control, nonreactive with the RHELAX RF

reagent.

Each batch of reagents undergoes rigorous quality

control at various stages of manufacture for its specificity,

sensitivity and performance.

Reagent Storage and Stability

1. Store the reagents at 2 to 8°C. Do not freeze.

2. The shelf-life of the reagent is as per the expiry date

mentioned on the reagent vial label.

Principle

The RHELAX RF slide test for detection of rheumatoid

factors is based on the principle of agglutination. The

test specimen is mixed with RHELAX RF latex reagent

and allowed to react. If RF is present within detectable

levels, then a visible agglutination is observed. If RF is

absent below detectable levels, then no agglutination is

observed.

Note

1. In vitro diagnostic reagent for laboratory and

professional use only. Not for medicinal use.

2. All the reagents derived from human source have

been tested for HBsAg and anti-HIV antibodies and

are found to be nonreactive. However, handle the

material as if infectious.

3. The reagent contains sodium azide 0.1% as preservative.

Avoid contact with skin and mucosa. On disposal,

flush with large quantities of water.

4. The reagent can be damaged due to microbial

contamination or on exposure to extreme temperatures.

It is recommended that the performance of the reagent

be verified with the positive and negative controls

provided with the kit.

5. Shake the RHELAX RF latex reagent well before use

to disperse the latex particles uniformly and improve

test readability.

Serology/Immunology 657

6. Only a clean and dry glass slide must be used. Clean

the slide with distilled water and wipe dry.

7. Accessories provided with the kit only must be used

for optimum results.

Specimen Collection and Preparation

No special preparation of the patient is required prior to

specimen collection by approved techniques.

Only serum should be used for testing. Should a delay

in testing occur, store the sample at 2 to 8°C. Samples

can be stored for up to a week. Do not use hemolyzed

serum.

Material Provided with the Kit

Reagent

Rhelax RF latex reagent, positive control, negative control.

Accessories

Glass slide with six reaction circles, sample dispensing

pipettes, mixing sticks, rubber teat.

Additional Material Required

Stopwatch, test tubes, high intensity direct light source,

isotonic saline.

Test Procedure

Bring reagent and samples to room temperature before use.

Qualitative Method

1. Pipette one drop of serum onto the glass slide using

the disposable pipette provided with the kit.

2. Add one drop of RHELAX RF latex reagent to the drop

of serum on the slide. Do not let the dropper tip touch

the liquid on the slide.

3. Using a mixing stick, mix the serum and the RHELAX

RF latex reagent uniformly over the entire circle.

4. Immediately start a stopwatch. Rock the slide

gently, back and forth, observing for agglutination

macroscopically at 2 minutes.

Semiquantitative Method

1. Using isotonic saline, prepare serial dilutions of the

serum sample positive in the qualitative method 1:2,

1:4, 1:8, 1:16, 1:32, 1:64 and so on.

2. Pipette each dilution of the serum sample onto

separate reaction circles.

3. Add one drop of RHELAX RF latex reagent to each

drop of the diluted serum sample on the slide.

Do not let the dropper tip touch the liquid on the

slide.

4. Using a mixing stick, mix the sample and the latex

reagent uniformly over the entire circle.

5. Immediately start a stopwatch. Rock the slide

gently, back and forth, observing for agglutination

macroscopically at 2 minutes.

Interpretation of Test Results

Qualitative Method

Agglutination is a positive test result and indicates the

presence of rheumatoid factors in the test specimen. No

agglutination is a negative test result and indicates the

absence of rheumatoid factors in the test specimen.

Semiquantitative Method

Agglutination in the highest serum dilution corresponds

to the approximate amount of rheumatoid factors in

IU/mL present in the test specimen.

To calculate the RF in lU/mL, use the following formula:

RF (IU/mL) = S × D

Where S = Sensitivity of the reagent, i.e. 10 IU/ mL.

D = Highest dilution of serum showing agglutination.

Remarks

1. Markedly lipemic, hemolyzed and contaminated

serum samples could produce non-specific results.

2. Use of plasma rather than serum can lead to false

positive results.

3. Do not read results beyond 2 minutes.

4. Rheumatoid factors are not exclusively found in

rheumatoid arthritis but sometimes in syphilis,

systemic lupus erythematosus, hepatitis, hypergammaglobulinemia also.

5. It is recommended that results of the test should be

correlated with clinical findings to arrive at the final

diagnosis.