To test for the presence of antibodies made against human im

To test for the presence of antibodies made against human immunodeficiency virus (HIV), you performed an indirect ELISA. The results of your experiment are shown below. Based on these results, which patient needs to be retested?

PATIENT A          0.378

PATIENT B           0.182

PATIENT C           1.254

Select one:

a. patient A

b. patient C

c. patient B

Solution

Ans. The ELISA reader gives absorbance of a sample obeying Beer-Lambert’s law. The absorbance of a sample shall be between 0 and 1 (i.e. 0.000 – 1.000). Because the Beer-Lambert’s law is valid for a certain range of specified solute concentration, an absorbance value greater than 1.000 may result deviation from the law (also, deviation from linearity or slope of the graph), thus may give erroneous results.   

The samples giving absorbance value greater than 1.000 are most often re-tested. For example, such samples may be diluted enough with distilled water to bring the absorbance reading below 1.000.

Thus,

Correct option: Patient C. 1.254           Note: Absorbance of sample is greater than 1.000