Tool measures capacity of Alzheimer's patients to give consent for research

Survey results tracked opinions from experts

A recent study of an instrument for assessing decisional capacity in patients with Alzheimer's disease shows that it's a reliable tool for determining whether those patients are competent to give their own consent for research.

The study, published recently in the American Journal of Geriatric Psychiatry, showed that scores patients received on a subsection of the MacArthur Competency Assessment Tool for Clinical Research (MacCAT-CR) tracked well with experts' opinions as to whether that patient was able to give consent.1

Jason Karlawish, MD, associate professor of medicine and associate director of the Penn Memory Center at the University of Pennsylvania in Philadelphia, says these results may help IRBs be more comfortable with the use of tools such as this one to help gauge decisional capacity.

Karlawish says IRBs need to consider tools such as the MacCAT-CR whenever a population under study has a reasonable probability of clinically significant cognitive impairment.

"Then it's worth thinking about what process or procedure you will have in place to assess capacity," he says. "We show one method, but by no means is that the method or the only method. That should be a function of the nature of the study's risks and benefits and complexity.

"But I think the field has reached the point where it's simply inappropriate to say that you cannot assess decisional capacity, which is a phrase that used to fly around out there."

Tool used in trial

Previous studies of the MacCAT-CR had shown it to be a reliable tool when used with patients who had mild to moderate Alzheimer's disease. This time, Karlawish and his colleagues studied its use in an actual clinical trial.

Karlawish's group studied 59 subjects who were participating in a clinical trial of simvastatin, a cholesterol-lowering drug being studied in the treatment of mild to moderate Alzheimer's disease. Each subject was accompanied by a study partner, an adult relative or friend who the subject trusted and who could serve as a knowledgeable aide to the subject.

The MacCAT-CR was administered to both the subjects and the study partners. The instrument itself is a semi-structured interview that is adapted to fit the specific information from the trial.

"This is not an instrument that has pre-specified questions with answers," Karlawish says. "It lets you plug relevant information from your clinical trial into structured questions with standardized scoring criteria."

The patient and study partner would have a written summary of the clinical trial, organized according to the sections outlined in the informed consent. After each section was read aloud, the interviewer would ask if there were questions, answer them, and then administer the questions from the MacCAT-CR pertaining to that section. Those results were tabulated.

Afterward, an audiotape of the interview was shown to three consulting psychiatrists who, without seeing the score or knowing the severity of the subject's illness, judged for themselves whether they thought the subject had sufficient capacity to give consent on his own.

Using a consensus of at least two out of three judges, 39 patients (53%) were found capable of giving their own consent. Comparing those results to the scores from the MacCAT-CR, the investigators found the scores — particularly the understanding subscore — highly predictive of the expert's opinion.

"In our paper, we're not even pushing the value of the other scales (included in the MacCAT-CR). We're saying if you just use the understanding subscale of the MacCAT, you get some decent information to structure your assessment of whether someone has adequate decisional capacity," he says.

No set cut-point

Karlawish says he was pleasantly surprised to see a reasonable proportion of patients were able to give their own informed consent.

"Even for those patients who were not capable, you were probably getting some information from them about their preferences and desires to be in research," he says.

He doesn't believe that it's necessary, or even desirable, to have one set cut-point for the MacCAT-CR — a score below which a subject is always incapable of giving consent. That cut-point could fluctuate from study to study, depending upon the risks involved. He notes previous studies have shown that experts' judgments of competency are dependent upon the risks of the research.

The cut-point also could vary based on the comfort level of the IRB, he says.

"There's no question that you can take the same protocol and give it to a variety of IRBs and you get back very different assessments of the research risks and benefits," he says. "It only logically follows that you get very different judgments about what are appropriate subject protections."

Reference

  1. Karlawish J, Kim SY, Knopman D, et al. Interpreting the clinical significance of capacity scores for informed consent in Alzheimer disease clinical trials. Am J Geriatr Psychiatry 2008 Jul;16(7):568-74.