An AQP1 allele associated with co(a-b-) phenotype.

The Colton (CO) blood group system consists of four antigens, Co(a), Co(b), Co3, and Co4, located on aquaporin-1 (AQP1), with Co(a) highly prevalent in all populations (99.8%). The Colton null phenotype, Co(a-b-), is very rare, and individuals with this phenotype lack the high-prevalence antigen Co3. To date, only six Co(a-b-) probands have been reported and four silencing alleles characterized. We identified an AQP1-null allele in a white woman with anti-Co3 caused by deletion of a G at nucleotide 601 (nt601delG) that results in a frameshift and premature termination (Val201Stop). Available family members were tested for the allele. Although anti-Co3 has been associated with mild to severe hemolytic disease of the fetus and newborn, the antibody was not clinically significant as evidenced by a low titer and delivery of asymptomatic newborns with moderate to weakly positive direct antiglobulin tests for all four pregnancies.

Hemolytic anemia associated with injection of fluorescein.

A 49-year-old woman presented with a hemoglobin level of 9.5 g per dL (95 g/L), reticulocyte count of 6.7 percent (0.067), and hemoglobinuria. The next day, the hemoglobin had dropped to 5.8 g per dL (58 g/L), and total bilirubin was 8.8 mg per dL (150 mumol/L). The serum reacted 2+ with all red cells (RBCs). The direct antiglobulin test (DAT) was 3+ with anti-IgG and 1+ with anti-C3, but eluates prepared by two different methods did not react with untreated RBCs. The eluate reacted 2+ with amoxicillin-coated RBCs; amoxicillin had been listed in the patient's record as a previous medication. The patient denied recent ingestion of amoxicillin. Further investigation documented the injection of a dye, fluorescein sodium (AK-FLUOR-25%), for a ophthalmologic fluorescein angiographic study 2 days before admission. RBCs coated with AK-FLUOR reacted with the eluate. Controls consisting of normal serum, an eluate prepared from DAT-negative RBCs, and a serum known to contain anti-penicillin did not react with AK-FLUOR-coated RBCs. Nine days later, the DAT was negative and the serum did not react with untreated RBCs. In the presence of AK-FLUOR (1-in-125) or amoxicillin (1 mg/mL), the serum reacted 2+ in the antiglobulin test. Antibodies to AK-FLUOR and amoxicillin appeared to react by two mechanisms, which is similar to results in recent reports of other drugs associated with hemolytic anemia. AK-FLUOR has not previously been reported to be associated with hemolytic anemia.