Doctors and nurses take so much blood from intensive care patients for testing that the patients become anemic and require transfusions, a new study concludes.

The study, published last week in The New England Journal of Medicine, found that in an average stay at Boston's Beth Israel Hospital, intensive care patients lost an average of almost two pints of blood to tests during their stay. In some cases, the amount of blood drawn was "exactly balanced by transfusions," suggesting that if fewer tests had been ordered, transfusions and their risk of infection might have been avoided, write Drs. Bruce R. Smoller and Margot S. Kruskall.

In patients with tubes implanted in their arms for easy access to blood samples, tests were taken up to six times a day.

The doctors did not say the tests were unnecessary. "Since we did not look at the indications for individual laboratory tests, we cannot evaluate the appropriateness of the tests ordered," they wrote.

But they did say smaller test tubes should be used, the same sample should be used for more than one test, and a cumulative total of the amount of blood drawn should be kept and checked before tests are ordered.

In an accompanying editorial, Dr. John F. Burnum laments: "The only two mammals to remove blood regularly from other mammals are vampire bats and humans." And he notes: "Vampire bats only occasionally attack humans."