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

 

Troubleshooting

Problem: False positive results

Possible causes Solutions

1. Plasma is used as a test specimen Only serum must be used for testing

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. Markedly lipemic, hemolyzed and contaminated serum samples Lipemic, hemolyzed and contaminated samples produce non-specific

results. Avoid such samples

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

out directly under the fan

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

clean and dry glass slides must be used for testing

Contd...

652 Concise Book of Medical Laboratory Technology: Methods and Interpretations Problem: False negative 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. 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. Samples can be stored for upto a week at 2–8°C.

4. Hemolyzed samples may be used for testing. Do not use hemolyzed samples for testing.

5. Prozoning due to high levels of CRP. CRP is an acute phase reactant; it is normal to have peaks in CRP levels in acute conditions

such as trauma, myocardial infarction and ischemic heart diseases.

Dilute the specimen and rerun the test.

Carry out a semiquantitative assay to determine the CRP level in

the sample.

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

comparision with another kit, other kit could be giving a false positive reaction.

Run the test with a third kit to validate results.

7. Decrease in drop size, thereby leading of 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.

Problem: Positive control giving negative reaction

Possible causes Solutions

6. 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 reagent

7. CRP levels increase in women who are on oral contraceptives Check the history of the patient

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 regent, hold the reagent dropper

vertically while dispensing the reagent

11. 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)