LETTERS TO THE EDITOR
tant as well as those variables that may be discovered to be important years later. Retrospective analyses of nonrandomized studies often find alternative explanations for what were thought to be treatment effects. It is possible for random assignment to produce nonequivalent groups, but the laws of probability make that very unlikely. As the number of patients goes up, that probability drops to a trivial concern. Biostatistics-like medicine-is, after all, applied probability. Science, unlike many other methods for seeking the truth, does not claim absolute certainty. The proper role of statistics is to quantify our degree of uncertainty. The question of how many sub jects are required in order to provide reasonable assurance that the treatment groups are sufficiently equivalent on all pretreatment variables can not be answered in the abstract. But the joint efforts of a thoughtful clinical researcher and an experienced statistician usually can estimate that number before the study is begun. The essential point I was attempting to make in Rule VIII is that if patients are assigned randomly to the treatment groups, one may legitimately make much stronger statements about the differences in group treatments being the cause of any differences in group outcomes than if one is without the assurance of group equivalence provided by random assignment. Randomization is not a magic ritual. It actually does produce pretreatment groups of strikingly similar characteristics. If the proper number of patients is randomly drawn from a defined population and randomly assigned to treatment groups, an individual cliician is then in a position to make predictions about a particular treatment for an individual patient, with a known degree of uncertainty. This is not perfect, but it is the most worthy goal of clinical research. And it is the justification for violating so many canons of good medical practice in the process. John ikf. Yancey, PhD Department of Growth and Special Care School of Dentistry University of L4ndville Louisville, KY
366
To the Editor:
The recent review article on blood transfusion in elective surgery by Drs. Goodnough and Shuck provides surgeons with extremely valuable and insightful information on the risks and options, including informed consent, of blood transfusions [I]. However, there is an error in the summary of the article where the authors state, “Here the homologous blood donor is given information identifying high-risk categories of people who should not donate blood, high-risk donors can withdraw from blood donation or identify themselves as high risk, confidentially, by checking a box indicating that the blood donated by them should be used for research purposes only. This screeningmechanism is not possible in designated blood donation since the blood donor is known to the transfusion recipient and is arguably nonvoluntary.” (Italics are mine.)
The error is the last sentence. Designated or directed blood donors must use a confidential unit exclusion method to indicate secretly if their blood should not be used or if it is to be used for transfusion [2]. If neither option is selected by the donor, the blood is discarded. Many directed donors are not individually known to the transfusion recipient. Deferred designated donors are never identified by name, test result, or reason for rejection to the intended transfusion recipient. Of greater importance is the administration of blood and blood components that are donated for a specific person (designated or directed donation) or for a patient’s own use (autologous), which blood, if not used by the intended recipient, may be transfused to other patients. This is called “crossing-over” in bloodbanking parlance. It is a common practice and likely accounts for more than 1% of all transfusions given in this country. Surgeons and other physicians may not know if crossingover is being done at their institution. The regional blood supplier can provide information about crossing-over to institutional medical and administrative staffs, if requested to do so. If designated blood transfusions are to be crossed-over to other pa-
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MARCH 1992
tients by physicians (?unknowingly), then a knowledgeable informed consent of this by the recipient of the intended transfusion should be obtained. Similarly, if autologous blood and components are transfused to patients other than the donor, an informed consent of this should be ob tained In conclusion, blood donation and transfusion are ofttimes lifesaving. But physicians must be knowledge able of blood industry practices that affect patient care, of which they may presently be unaware. This letter points out such a practice. Kenneth Fawcett, MD Transfusion Service St. Joseph Hospital Flint, MI 1. Goodnough LT, Shuck JM. Risks, options, and informed consent for blood transfusion in elective surgery. Am J Surg 1990; 159: 602-9. 2. Standards for blood banks and transfusion services. 13th ed. Arlington, VA: American Association of Blood Banks, 1989. In Response:
We stand by our sentence referenced by Dr. Fawcett on designated blood transfusion, in which we stated that the confidential exclusion screening mechanism that is in place for homologous blood donors is not possible for directed donors, since directed donors are known to the recip ients and are arguably nonvoluntary. We agree that all blood donors are required to use this method, but we argue that it is not effective for designated donors to the same extent as it is for homologous donors. Dr. Fawcett echoes our reservations about the effectiveness of this screening mechanism when he suggests that potential recipients of crossed-over designated blood be informed of the donor origins of the blood. If the confidential donor screening mechanism for designated donors was regarded to be as effective as for homologous donors, such information would not be necessary. The issues related to cross-over of unused designated or autologous blood to other transfusion recipients can perhaps best be dealt with by having as little of this blood as possible available for cross-over. We believe that patients who request direct-
tant as well as those variables that may be discovered to be important years later. Retrospective analyses of nonrandomized studies often find alternative explanations for what were thought to be treatment effects. It is possible for random assignment to produce nonequivalent groups, but the laws of probability make that very unlikely. As the number of patients goes up, that probability drops to a trivial concern. Biostatistics-like medicine-is, after all, applied probability. Science, unlike many other methods for seeking the truth, does not claim absolute certainty. The proper role of statistics is to quantify our degree of uncertainty. The question of how many sub jects are required in order to provide reasonable assurance that the treatment groups are sufficiently equivalent on all pretreatment variables can not be answered in the abstract. But the joint efforts of a thoughtful clinical researcher and an experienced statistician usually can estimate that number before the study is begun. The essential point I was attempting to make in Rule VIII is that if patients are assigned randomly to the treatment groups, one may legitimately make much stronger statements about the differences in group treatments being the cause of any differences in group outcomes than if one is without the assurance of group equivalence provided by random assignment. Randomization is not a magic ritual. It actually does produce pretreatment groups of strikingly similar characteristics. If the proper number of patients is randomly drawn from a defined population and randomly assigned to treatment groups, an individual cliician is then in a position to make predictions about a particular treatment for an individual patient, with a known degree of uncertainty. This is not perfect, but it is the most worthy goal of clinical research. And it is the justification for violating so many canons of good medical practice in the process. John ikf. Yancey, PhD Department of Growth and Special Care School of Dentistry University of L4ndville Louisville, KY
366
To the Editor:
The recent review article on blood transfusion in elective surgery by Drs. Goodnough and Shuck provides surgeons with extremely valuable and insightful information on the risks and options, including informed consent, of blood transfusions [I]. However, there is an error in the summary of the article where the authors state, “Here the homologous blood donor is given information identifying high-risk categories of people who should not donate blood, high-risk donors can withdraw from blood donation or identify themselves as high risk, confidentially, by checking a box indicating that the blood donated by them should be used for research purposes only. This screeningmechanism is not possible in designated blood donation since the blood donor is known to the transfusion recipient and is arguably nonvoluntary.” (Italics are mine.)
The error is the last sentence. Designated or directed blood donors must use a confidential unit exclusion method to indicate secretly if their blood should not be used or if it is to be used for transfusion [2]. If neither option is selected by the donor, the blood is discarded. Many directed donors are not individually known to the transfusion recipient. Deferred designated donors are never identified by name, test result, or reason for rejection to the intended transfusion recipient. Of greater importance is the administration of blood and blood components that are donated for a specific person (designated or directed donation) or for a patient’s own use (autologous), which blood, if not used by the intended recipient, may be transfused to other patients. This is called “crossing-over” in bloodbanking parlance. It is a common practice and likely accounts for more than 1% of all transfusions given in this country. Surgeons and other physicians may not know if crossingover is being done at their institution. The regional blood supplier can provide information about crossing-over to institutional medical and administrative staffs, if requested to do so. If designated blood transfusions are to be crossed-over to other pa-
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MARCH 1992
tients by physicians (?unknowingly), then a knowledgeable informed consent of this by the recipient of the intended transfusion should be obtained. Similarly, if autologous blood and components are transfused to patients other than the donor, an informed consent of this should be ob tained In conclusion, blood donation and transfusion are ofttimes lifesaving. But physicians must be knowledge able of blood industry practices that affect patient care, of which they may presently be unaware. This letter points out such a practice. Kenneth Fawcett, MD Transfusion Service St. Joseph Hospital Flint, MI 1. Goodnough LT, Shuck JM. Risks, options, and informed consent for blood transfusion in elective surgery. Am J Surg 1990; 159: 602-9. 2. Standards for blood banks and transfusion services. 13th ed. Arlington, VA: American Association of Blood Banks, 1989. In Response:
We stand by our sentence referenced by Dr. Fawcett on designated blood transfusion, in which we stated that the confidential exclusion screening mechanism that is in place for homologous blood donors is not possible for directed donors, since directed donors are known to the recip ients and are arguably nonvoluntary. We agree that all blood donors are required to use this method, but we argue that it is not effective for designated donors to the same extent as it is for homologous donors. Dr. Fawcett echoes our reservations about the effectiveness of this screening mechanism when he suggests that potential recipients of crossed-over designated blood be informed of the donor origins of the blood. If the confidential donor screening mechanism for designated donors was regarded to be as effective as for homologous donors, such information would not be necessary. The issues related to cross-over of unused designated or autologous blood to other transfusion recipients can perhaps best be dealt with by having as little of this blood as possible available for cross-over. We believe that patients who request direct-
