Can your blood type be changed?

Update: The answer is “Yes”. Scroll down to see more than one case and an rh negative changing into an rh positive and vice versa.

This is one claim that has been made a lot. And until recently I have never received additional information to any of the claims I have heard.
Then of course there are cases of chimerism where you have different blood types in your veins. And one test can show one blood type, another test the other.
There is however one story out there which documents Demi-Lee Brennan and the 1 in 6 Billion possibility of a transplant changing your blood type.

The 15-year-old liver transplant patient is the first person in the world to take on the immune system and blood type of her donor, negating the need to take anti-rejection drugs for the rest of her life. The phenomenon, which has been documented in the New England Journal of Medicine, has amazed doctors, who say they have no idea how it occurred.

She had the liver transplant done and then:

Nine months later, when her condition worsened and she was readmitted, doctors were shocked to find that her blood type had changed. The head of hematology, Julie Curtin, said she was stunned when she realised Demi-Lee was now O-positive, rather than O-negative.

“I was convinced we had made a mistake, so we tested it again and it came up the same. Then we tested her parents and they were both O-negative, so it was confirmed that Demi absolutely had to have been O-negative.”

You can read more of the story here:

Transplant girl’s blood change a ‘miracle’

But as I have stated before, reading a mainstream newspaper article is one thing (the interpretation of sometimes not sufficiently educated journalists can potentially bring the wrong conclusions) … finding the actual study is another thing:

Acute fulminant hepatitis after a nonspecific viral illness developed in a previously well 9-year-old girl. Her blood group was O, RhD-negative. She was referred to our institution, and at the time of admission she had markedly elevated aminotransferase levels and evidence of marked synthetic dysfunction. Extensive testing ruled out known viral, metabolic, drug-related, and autoimmune causes, and a diagnosis of “non–A-to-G viral hepatitis” was made. A liver biopsy was not performed because of severe underlying coagulopathy.

Given the patient’s fulminant hepatic failure requiring mechanical ventilation, urgent liver transplantation was performed with the use of a whole-organ transplant from an O, RhD-positive 12-year-old male donor who was positive for cytomegalovirus (CMV) (the recipient was also CMV-positive) and who died of hypoxic brain injury. The whole liver was transplanted (cold ischemic time, 9 hours 46 minutes), and the biliary anastomosis was a choledochocholedochostomy. The HLA status of the donor was A34,68;B50,76;DR4,13, and the recipient’s HLA status was A2,24;B37,62;DR7,9.

Nine months after transplantation, a small-bowel obstruction developed, requiring surgical division of adhesions and resection of an ileal band. Routine preoperative blood grouping revealed that the patient’s blood group had changed from O, RhD-negative, to O, RhD-positive (the donor’s blood group), and a weakly positive direct antiglobulin test indicated coating of red blood cells with IgG antibodies. At that time, there was no evidence of spherocytosis on the blood film to suggest hemolysis; the hemoglobin level was 95 g per liter. This finding was confirmed by the Australian Red Cross Blood Service. Both parents had group O, RhD-negative blood with the phenotype ccdee, whereas their daughter’s phenotype was now cDEe. However, serum samples showed mixed-field reactions with anti-D and anti-E typing.

Source and more:

How a liver transplant has changed a young girl’s rh factor

So this was an rh negative person changing into an rh positive. Can it be the other way around? Yes.
See this:

We report a female patient whose Rh phenotype shifted from RhD-positive to RhD-negative over a 3-year period (1991–94), during which time she was treated with mastectomy (1992) and local irradiation for a low-grade recurrent breast cancer. She was diagnosed with chronic myeloid leukaemia in 1994, and has since then received chemotherapy. The patient was repeatedly typed as O, RhD-positive between 1965 and 1991 and was repeatedly found RhD-negative after 1994. Bcr-Abl transcripts typical of Ph1 chromosome were detected. Molecular analysis indicated that the patient was heterozygous at the RH locus, carrying one haplotype in which the RHD gene exhibited a single nucleotide deletion (G600) resulting in a frameshift and premature stop codon, and a normal RHCE gene (allele Ce). The second haplotype contained only the RHCE gene (allele ce) and was normal. Further analysis carried out on total leucocytes, purified neutrophils, EBV-lymphoblastoid cell line and cultured erythroblasts indicated that the G600 deletion was restricted to the myeloid lineage. No modification of other blood group antigens could be detected. These findings suggest a somatic mutation which most probably occurred in a stem cell common to the myeloid lineage.

Source:
Shift from Rh-positive to Rh-negative phenotype caused by a somatic mutation within the RHD gene in a patient with chronic myelocytic leukaemia