Potential Experimental Problems and Limitations of the Test
ELISA is used in many laboratories to determine whether a particular antibody is present in a patient's blood sample. Although the procedure is routine and straightforward, it involves a number of variables, such as reagent selection, temperature, volume measurement, and time, which if not adjusted correctly can affect subsequent steps and the test outcome.
This general test has some important limitations:
- A positive result correctly confirming the presence of an antibody does not necessarily mean the patient is sick. The body can continue to produce antibodies even though the person may have had the disease earlier and recovered.
- People may be poor producers of an antibody or may have some interfering substance in their blood. The amount of antibody, consequently, may be too low to measure accurately or may go undetected. This result is termed a false negative.
- A positive result may occur if an unrelated antibody reacts with the antigen non-specifically. Unlike a true positive result in which the specific antibody is detected, however, this positive reaction is false. Testing many patients and running tests more than once helps lab workers distinguish a true result from a false one. To avoid simple experimental mistakes leading to incorrect results, scientists conduct tests using duplicate (or sometimes more than two) samples.