Adverse Reactions to Stroma Free Hemoglobin Stroma free hemoglobin offers a great potential as a blood substitute. There have been many successful trials in laboratory animals and some researchers have already started clinical trials in humans. However, all of the clinical studies in humans to date have reported some form of adverse reactions. These have been attributed to:

Preparations that are now being used are much purer than earlier preparations. The processing that the hemoglobin solution goes through makes the preparations virtually free of red cell stroma and endotoxin. Thus, making comparisons of results of recent studies with earlier trials using less purified hemoglobin solutions invalid.

At least in theory, allergic or anaphylactic reactions can occur if an animal is repeatedly transfused with hemoglobin from another species. Allergic reactions do not occur if homologous hemoglobin is used. This is unfortunate since bovine hemoglobin, which would be readily available from slaughterhouses is much more efficient at carrying oxygen than is human hemoglobin. Bovine hemoglobin has a P50 of 28 to 30 mm Hg compared to 10 to 12 mm Hg for human hemoglobin.

None of the human trials that have been done with stroma free hemoglobin have resulted in the recipients forming antibodies to the hemoglobin. However, in one trial using a human hemoglobin preparation, weak anti-species antibodies were stimulated in primates transfused with repeated courses of hemoglobin solution if injected with an adjuvant. Antibodies were not produced if the adjuvant was not presented.

On the otherhand, rats repeatedly transfused with human hemoglobin by Chan et al suffered anaphyactic reactions. Therefore, the more dissimilar the species of the recipient and the hemoglobin donor, the higher the probability of antibody production.

None of the animal studies that were performed as background for the few human trials that have been attempted have predicted all of the adverse effects seen in the human studies which followed. This may prolong the approval process for these products by the FDA.

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