DIAGNOSIS OF DISEASE BASED ON IMMUNE RESPONSE—A VIRTUAL LABORATORY EXERCISE
Components of the immune system called antibodies are found in the liquid portion
of blood and help protect the body from harm. Antibodies can be used also outside
the body in a laboratory-based assay to help diagnose disease caused by
malfunctions of the immune system or by infections.
Potential Experimental ProblemsELISA 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 virtual laboratory has been developed so that when a mistake is made, you will not get the correct answer. The program keeps track of errors made throughout the experiment and generates a report at the end.
Limitations of the TestThis general test has some important limitations.
First, a positive result correctly confirming the presence of 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.
Second, people may be poor producers of 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.
Third, a positive result may occur if an unrelated antibody reacts with the antigen nonspecifically. Unlike a true-positive result where 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 from a false result. To avoid simple experimental mistakes leading to incorrect results, scientists conduct tests using duplicate (or, sometimes, more than two) samples.
Begin with the Background describing the experiment.