College of American Pathologists
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  Q and A






January 2008

Question Q. I recently instituted a test for estimated glomerular filtration rate, or eGFR, in my laboratories, and it is well received. However, one question has arisen for which I am unable to find an answer. There is a correction factor to be applied if a patient is African American. There are many shades of this, as we in the United States are a melting pot. What percentage African American do you have to be to apply this correction factor?

A. The Modification of Diet in Renal Disease Study equation includes a term for African-American race to account for the fact that for the same level of serum creatinine, the African Americans included in the study had a higher glomerular filtration rate than Caucasians and other races. This is due to a higher average muscle mass and, therefore, higher creatinine generation rate in African Americans.

This term was validated in analyzing participants who were screened for inclusion in the African American Study of Kidney Disease and Hypertension. Within these studies, race was assigned by participant self-report. It is therefore recommended to use patient self-assigned race to determine whether the term for African American should be used. More research is required to better address this question and to understand how best to apply this equation in other racial and ethnic groups.

Lesley A. Stevens, MD, MS
Assistant Professor of Medicine
Tufts University School of Medicine

Question Q. It is our policy not to accept back into inventory red blood cell units that have been out of our control for more than 30 minutes. However, a blood transfusion may take up to four hours. What should we do if the start of a transfusion is unavoidably delayed beyond 30 minutes after the unit is issued? Is it acceptable to begin a transfusion after this time, provided it can still be completed within four hours?

A. Yes. The purpose of the commonly applied “30-minute rule” is to ensure that units returned to inventory are still suitable for transfusion. A unit could be subjected to several false starts before being transfused.

The time limit is based on an assumption that the unit’s temperature will not exceed 10ºC for at least the first 30 minutes at room temperature. As this temperature is the maximum allowed for shipping red blood cells, the unit should be expected to be safe and efficacious for transfusion to another recipient after re-refrigeration. Exposing the unit to room temperature for a prolonged period would accelerate the consumption of glucose and could exhaust this necessary substrate before the end of the re-started storage period. Furthermore, at least theoretically, warming the unit might accelerate growth of contaminating bacteria.

The 30-minute limit is arbitrary,1 and the unit does not become dangerous or ineffective at the 31st minute,2 but the limit must be placed somewhere. Therefore, if a transfusion were unexpectedly and unavoidably delayed a few minutes beyond the 30-minute limit, the unit could still be transfused. The four-hour maximum for a transfusion is to keep bacteria from proliferating. This transfusion time can be met in most circumstances, even with a late start.

Limiting the post-issuance starting time also ensures that a transfusion begins promptly, so the unit is not stored in the patient care area and mistakenly transfused to the wrong recipient. Double-checking with the nurse when the unit is requested that the transfusion is set to begin can minimize the frequency of unexpected delays in initiating a transfusion.


  1. Hamill TR. The 30-minute rule for reissuing blood: Are we needlessly discarding units? Transfusion. 1990;30:58–62.
  2. Reid TJ, Babcock JG, Derse-Anthony CP, et al. The viability of autologous human red cells stored in additive solution 5 and exposed to 25°C for 24 hours. Transfusion. 1999;39:991–997.

James P. AuBuchon, MD
E. Elizabeth French Professor
Chair, Department of Pathology
Dartmouth-Hitchcock Medical Center
Lebanon, NH

Chair, CAP Transfusion
Medicine Resource Committee