Q and A

January 2007

Q. Our local hospitals routinely crossmatch all patients we send for blood transfusions. Why not simply do an immediate spin, test against the panel cells (screening for antibodies), and, if no alloantibodies are present, take a bag of group-compatible cells off the shelf, rather than do a long and laborious full crossmatch?

A. Indeed, why not? Your question raises the issue of judicious use of precious resources—both laboratory materials and staff.

Some laboratories began depending on an antibody screen rather than an antiglobulin phase (“full”) crossmatch to detect clinically significant red cell alloantibodies over 25 years ago. Once a patient has been shown not to have any currently (or previously) detectable clinically significant antibodies, an immediate spin or electronic crossmatch can be used to provide a transfusion that can be predicted to be compatible in vivo with a high degree of certainty. (Only antibodies to low-frequency antigens would not be detected, and these rarely cause significant morbidity.)

However, the key to applying this approach successfully is a dependable result from the antibody screen. Many hospitals with low transfusion volumes or that rotate techs among multiple sections of the lab may be concerned about the reliability of the screen’s negativity and prefer to double-check that result with an antiglobulin phase serologic crossmatch. (Blood bankers are well known for wearing both belts and suspenders.) One could argue that any tech working in any transfusion service laboratory needs to have demonstrated initial and continuing competency in performing all basic tasks, such as antibody screening, and thus the use of an immediate spin crossmatch should be able to be implemented safely in any laboratory.

Laboratories that still apply an antiglobulin phase crossmatch for all transfusions may want to take a moment and evaluate the credibility of their competency assessments. If the assessments are to be believed, then pretransfusion testing procedures may be simplified safely. If not, then they need to be bolstered to ensure accurate performance, not only of antibody screens but also of all tests performed.

James P. AuBuchon, MD
E. Elizabeth French Professor and Chair of Pathology
Dartmouth-Hitchcock Medical Center
Lebanon, NH
Chair, CAP Transfusion
Medicine Resource Committee

Q. Do we need to use a Fyrite gas analyzer to monitor daily our CO₂ incubator in microbiology, or is the digital readout sufficient?

A. The laboratory must have a procedure in place for daily monitoring and recording of CO₂ levels in each CO₂ incubator. It is necessary initially to validate the digital readout as part of your equipment validation using an external device, such as a Fyrite analyzer. After validation, the frequency of the external check must be defined by your laboratory in your equipment quality control procedure and should occur, at a minimum, at the frequency recommended by the manufacturer. For daily monitoring to ensure the environment is maintained at an appropriate range for CO₂ content, it is acceptable to monitor and record the CO₂ level from the digital readout of the incubator.

We do not recommend using organisms as a sole means of monitoring CO₂ content. An organism may be used as an adjunct to mechanical monitoring and would be a good indicator of a potential problem. The organism used must be directly affected by the level of CO₂ in the incubator to be a reliable monitor.

CAP microbiology checklist question MIC.21813, phase I, reads:

Are CO₂ incubators checked daily for adequate CO₂ levels, with recording of results?

Note: Some organisms require CO₂to grow sufficiently to form visible colonies. CO₂monitoring is required in all CO₂incubators, including those that adjust gas flow to maintain a set CO₂level, to ensure that the environment is within an acceptable range for CO₂content. It is acceptable to monitor and record CO₂levels from digital readouts; however, the laboratory must verify that the readout is accurate (by initial calibration or Fyrite). The frequency of verification must be defined in the laboratory’s equipment quality control procedure and should be performed, at minimum, at the frequency recommended by the manufacturer.

Carolyn Gandy
Technical Specialist
Laboratory Accreditation Program
College of American Pathologists
Northfield, Ill.