Titers are a measurement of how much antibody a human may have. There are other titers for other types of organisms; however, for CNAs we are just talking about the titers that are found through a blood test CNAs may have to do before being hired. This blood test is taken for different reasons. It might be to test for how immune a CNA is to a disease like hepatitis A, B, or C.
Other titers can test for Coombs in pregnant women. To find if the patient is negative or positive the test has to be done, where the test is looking for the amount of antibodies in the blood test for a specific disease. There is a dilution ratio given that determines positive or negative.
Any time a person is given a vaccination it is in order to make the person immune to a disease. However, there are certain levels of immunity in which a person may be indirectly immune, but could become ill from that disease given the right circumstances. Basically titers look for sufficient immunity to whatever disease is being considered.
Since titers are a blood draw some CNAs are going to be taught how to take blood from their patient. Typically, blood draws are in the arms, where the veins are easier to see and feel. However, if the arm does not work the CNA may look at the back of the hand to find a vein that will provide a good blood sample.
The CNAs must get enough blood for the lab to run the test. Since a dilution will be created in order to count how many antibodies are in the blood it can require a bit, especially if the test needs to be run again.
It is impossible for the lab to determine if you have developed natural antibodies to certain diseases or if the vaccination was responsible. All the lab test can confirm is that there are antibodies in your system. It is also possible to confirm if a person currently has the disease, been vaccinated for it, or if they ever had the disease because of the presence of the antibodies. There are issues with false negatives sometimes because of the period of time an infection can take to become the disease. It will depend on the disease. CNAs are just asked to run the blood draw for the titers, rather than to complete the test. (Certain states allow CNAs to draw blood, while others will not.)