3. Samples stored for a long period of time are used as specimens Sample can be stored for upto a week at 2–8°C. Only serum must be

 

3. Anti-DNP may be found in diseases other than

SLE. Low titers have been detected in rheumatoid

arthritis, chronic hepatitis, periarteritis nodosa,

dermatomyositis, scleroderma, atypical pneumonia,

tuberculosis and lymphoma.

Troubleshooting

Problem: False positive results

Possible causes Solutions

1. Contamination of the latex reagent with positive control or positive

sample

Precaution should be taken so that the dropper tip of the reagent does

not touch the samples and controls on the glass slide

2. Samples are stored for a long period Should a delay in testing occur, store samples at 2–8°C. Samples can

be stored for upto a week at 2–8°C

3. Cross contamination due to the usage of the same mixing stick Separate mixing stick should be used for mixing the controls and the

sample

4. Markedly lipemic, hemolyzed and contaminated serum samples Using lipemic, hemolyzed and contaminated samples produce nonspecific results. Avoid using such samples

5. Drying of the reagent on the slide Do not read results beyond 2 minutes. The test should not be carried

out directly under the fan

6. Presence of dust or debris on the glass slide used Dust or debris could be misinterpreted as agglutination therefore only

can dry glass slides must be used for testing

7. Latex particles contaminated with positive control/positive sample Care must be taken to see that the latex reagent dropper tip does not

touch the sample or control taken on the slide during dispensing of

the reagen

8. Wrong dropper used for dispensing the sample Accessories provided with the kit only must be used for optimum

results

9. Increase in drop size, thereby leading to excess reagent dispensed Excess reagent dispensed gives false positive results at borderline

concentrations. Ensure that exactly one drop of reagent is dispensed

onto the slide

10. Reagent dropper not held vertically while dispensing To ensure accurate dispensing of the reagent, hold the reagent dropper vertically while dispensing the reagent

11. Cross contamination due to the usage of the same mixing stick Separate mixing stick should be used for mixing the controls and the

sample

12. Dried latex particles observed in the latex reagent:

• During slide test with negative control

•  In the dropper of the vial (due to freezing of the latex reagent

during storage)

• Improper dispensing of the entire 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

13. Low titers of Anti-DNP may also be found in clinical conditions

such as RA, chronic hepatitis, periarteritis nodosa, dermato myosis, Scleroderma, atypical pneumonia, tuberculosis and lymphoma.

The clinical history of the patient should be checked for any of these

disorders

662 Concise Book of Medical Laboratory Technology: Methods and Interpretations Problem: Delayed positive results

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. Reagents not brought to room temperature before testinG Bring the reagents to room temperature before carrying out the test

Possible causes Solutions

1. Cold reagents have been tested The reagents should be tested only after attaining room temperature

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 as negative Shake the latex reagent well before use to disperse the latex particles

uniformly and improve test readability

3. Samples stored for a long period of time are used as specimens Sample can be stored for upto a week at 2–8°C. Only serum must be

used for testing

4. Sample may be hemolyzed or contaminated Avoid using hemolyzed or contaminated samples for testing

5. 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 results

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

RF present in the sample thereby leading to false negative results

Problem: Positive control giving negative reaction

Problem: Delayed agglutination

AUSTRALIA ANTIGEN HBSAG (VIRUTEX HBsAg)

(Courtesy: Tulip Group of Companies)

Slide Test for Hepatitis B Surface Antigen

Summary