If you have an undetectable viral load, the likelihood of your CD4 cells dropping significantly is so small that getting a CD4 test more than yearly is probably a waste of time, money and any anxiety it may cause. In a study of 832 people receiving HIV care at the U.S. Department of Veterans Affairs between 1998 and 2011, 93 percent kept their CD4s above 200—crucial for preventing opportunistic infections—if they were virally suppressed. Researchers deduced that those with an undetectable viral load and CD4s at or above 300 would have a 97 percent probability of keeping them above 200 for a four-year period. This likelihood increases to 99 percent when non-HIV-related causes of CD4 drops are factored out.