What happens when doctors have trouble arriving at a definitive ADHD diagnosis? Typically, the next step is a standard series of tests and evaluations -- not so much to diagnose ADD as to determine whether conditions like learning disorders or neurological problems are involved -- instead of, or in addition to, ADD.
When low IQ or a learning disorder is suspected, intelligence and academic achievement tests are usually called for. "Probably 40 percent to 50 percent of the children we see should have this kind of comprehensive evaluation," says psychologist Ricardo Eiraldi, Ph.D., of the Children's Hospital of Philadelphia and a member of the CHADD scientific advisory board.
Neuropsychological testing (a battery of tests that measure brain functions like memory, attention, fine motor skills, and decision-making abilities) is needed less frequently -- about 5 percent of the time, Dr. Eiraldi says. "It's usually for kids with a possible neurological problem -- they have severe tics or a history of seizures. Otherwise, it's overkill. Testing takes up to eight hours, and it's expensive."
Neuropsych testing is more frequently used for adults with possible ADD. "We do it in cases of diagnostic uncertainty," says Lenard Adler, M.D., director of the adult ADHD program at New York University -- such as when an adult can't remember whether he had similar problems in childhood (a requirement for the diagnosis). A college may require test results before granting ADD accommodations. "Still, we test only 15 percent of the adults who come to our program," says Dr. Adler.
Continuous performance testing (CPT), a relative newcomer to ADD evaluation, is a computerized system that measures attention and impulse control. During the test, which lasts about 20 minutes, the patient is asked to perform a basic task, like press a button as quickly as possible whenever a certain image appears on the screen (for example, an "X" in a rapid succession of letters).
CPT adds information, but "it's not very useful diagnostically," Dr. Eiraldi says. "It gives too many false positives and negatives." Andrew Adesman, M.D., chief of developmental and behavioral pediatrics at Schneider Children's Hospital, in Glen Oaks, New York, says CPT provides "an imperfect piece of data that needs to be viewed in the context of a much broader picture."
In fact, from the experts' point of view, all any test can do is add detail to a picture that, after all is said and done, may still be unclear. "Parents are often hoping for an objective test that will reveal what's wrong," Dr. Adesman says. "But we don't have any lab measure that gives us that kind of diagnostic certainty."