• Improper dispensing of the nature reagent from dropper

Immediately after performing the test, transfer the contents of the

reagent dropper back into the reagent vial

Ensure that no reagent is left behind in the dropper. Close the cap

of the reagent vial properly and store it back at 2–8°C

Do not freeze the reagent vial

Contd...

Problem: Delayed agglutination

Possible causes Solutions

1. Reagents not brought to room temperature before testing. Bring the regents to room temperature before carrying out the test.

Problem: False negative results

Possible causes Solutions

1. The reagent may be damaged due to microbial contamination or

exposure to extreme temperatures

Performance of the reagents can be verified by using positive control/

known positive sample

2. Weak agglutination may be interpreted Shake the latex reagent well before use to disperse the latex particles

uniformly and improve the test readability

3. Prozoning due to antibodies to streptolysin O being in concentrations greater than 4000 IU/mL

Dilute the serum and check for agglutination. If no agglutination is

observed with the neat sample but agglutination is observed with the

diluted sample, then it may be due to prozoning. Determine the titer

of ASO

4. Samples stored for a long period of time are used as specimens Samples can be stored for upto a week at 2–8°C

5. Hemolyzed samples may be used for testing Avoid using hemolyzed samples.

6. If the conclusion of false negative results has been arrived at by

comparison with another kit, this other kit could be giving a false

positive reaction

Run the test with a third kit to validate the results

7. Decrease in drop size, thereby leading to less amount of reagent

dispensed

Less amount of reagent dispensed gives false negative results at

borderline concentrations. Ensure that exactly one drop of reagent is

dispensed onto the slide

8. The latex reagent might have been frozen The latex reagent should never be frozen as freezing leads to the dissociation of human IgG coated on the latex. The free IgG neutralizes

the RF present in the sample thereby leading to false negative results

656 Concise Book of Medical Laboratory Technology: Methods and Interpretations Possible causes Solutions

1. The positive control may have deteriorated due to contamination

or exposure to extreme temperatures

Check the performance of the latex reagent; using known positive

samples, if the latex reagent is working then the positive control may

have deteriorated

Possible causes Solutions

1. The sensitivity of our kit is 200 IU/mL hence, if the other kit has

a cutoff of more or less than 200 IU/mL then the other kit may

produce a false positive/negative result accordingly

Check the sensitivity of the other kit with known true ASO calibrator

Problem: Positive control giving negative reaction

Problem: Positive result with this kit and negative with other kit or vice versa

SLIDE TEST FOR RHEUMATOID FACTORS

(RHELAX RF)

(Courtesy: Tulip Group of Companies)

Summary

Sometimes autoantibodies are produced by the human

body against self-antigens. The precise role that this

aberrant immunity plays in the pathogenesis of certain

rheumatic diseases is unknown. However, the presence of

these autoantibodies serve as credible marker of the disease.