New Orleans, LA - One cup of coffee does not seem to affect the result of an adenosine SPECT imaging test, according to a new study presented at last week's American Heart Association Scientific Sessions 2004.

Dr Gilbert Zoghbi (University of Alabama, Birmingham) explained that caffeine is believed to attenuate the coronary hyperemic response to adenosine by competitive blockade of the A_2a receptor, and caffeine is commonly withheld before adenosine SPECT perfusion imaging so as not to mask ischemia detection. In fact, many such tests are canceled if the patient has had a cup of coffee for breakfast.

Zoghbi and his colleagues hypothesized that since the interaction between caffeine and adenosine is competitive, a cup of coffee is unlikely to mask ischemia, as caffeine blood levels would be low relative to adenosine levels.

To evaluate this further, they performed a study in 30 coronary heart disease patients who underwent two adenosine SPECT imaging studies, the first without caffeine on board and the second one hour after the patient had drunk one cup of 8 ounces of regular coffee. Results showed that the average caffeine blood level was 3.1 mg/L one hour after intake and that this did not have any significant effects on the test results. The sum difference score reflecting ischemia was 3.8 before and 3.9 after caffeine, the abnormality as shown by polar maps was 11.8% at baseline and 12.1% after caffeine, and the left ventricular ejection fraction by gated SPECT was 50 at baseline and 51 after caffeine.

The researchers concluded that these results have important implications with respect to patients who ingest caffeine before adenosine stress testing and have their tests canceled. But Zoghbi said he thought that more studies needed to be conducted, testing different doses of caffeine, before guidelines were changed.

Asked if "coffee was coffee," or did it make a difference what sort of coffee a patient had drunk, ie, "is Starbucks coffee different from that in the hospital canteen," Zoghbi said the caffeine content of a cup of coffee could vary from 90 mg to 300 mg. "There probably is a dose-response effect, so we should do more work on this," he commented.

However, a recent review of the field suggests that caffeine could interfere with vasodilator stress perfusion studies, including those using adenosine,[1] and the authors recommend that all patients undergoing such studies should be advised not to consume any caffeine-containing food or drink for 48 hours beforehand.