To the Editor,
The P antigen is a high-incidence antigen present in erythrocytes, platelets, lymphocytes, fibroblasts, the placenta and uroepithelial cells. More than 99.9% of the population has this antigen. Individuals with P phenotype are characterised by a lack of Pk, P and P1 erythrocyte antigens and by forming anti-Tja antibodies (anti-PP1PK), without previous immunization. Knowledge of this type of antibodies is important because they are involved in severe post-transfusion reactions.1
CASE REPORT
The patient was a 68-year-old female, whose only history of significance was iron deficiency anaemia, examined by Gastroenterology since May 2013, with no history of nephrology problems. Following progressive anaemia (haemoglobin: 6.5g/dl), the patient was referred to the hospital centre for a red blood cell transfusion. We observed a post-transfusion reaction and progressive deterioration of renal function, reaching a maximum creatinine level of 7.67mg/dl, urea 171mg/dl and oligoanuria. The patient was admitted to the Nephrology Department, where a complete study was carried out. We observed values of haemoglobin up to 4.2mg/dl, LDH 997UI/l, indirect bilirubin 1.1mg/dl, reticulocytes 2.9%, haptoglobin 36.40mg/dl and anisopoikilocytosis with polychromasia in the blood smear. Haematuria and pyuria were detected in the urine test strip. The data suggested autoimmune intravascular haemolytic anaemia due to blood incompatibility.
The Haematology Department was consulted, which reported the presence of irregular antibodies of anti-Tja specificity at a titre of 1:16. These results are compatible with the absence of a high-incidence antigen in the general population, the P antigen. During the hospital admission, renal function improved. The patient required various sessions of haemodialysis, support treatment with intense fluid therapy and alkalinisation, and treatment of anaemia with erythropoietin and intravenous iron, and four units of packed erythrocyte transfusion. Currently the patient has a creatinine level of 0.3mg/dl and haemoglobin level of 10.6g/dl.
DISCUSSION
This case covers two conditions rare in normal clinical practice: the absence of the P antigen and acute renal failure (ARF) due to haemoglobinuria. Despite the diagnostic suspicion being intravascular haemolytic anaemia secondary to blood incompatibility, doubts arose due to the urine testing negative for haemosiderin and haemoglobin, as well as in the Coombs test.
The absence of the P, Pk and P1 antigens, structurally related, occurred as a result of the loss of activity of 4-alpha-galactosyltransferase, a type II membrane protein with 353 amino acids. In addition to being associated with post-transfusion reactions, it can also cause abortions through haemolytic disease of the fetus and newborn and, according to some theories, different infectious diseases (infectious erythema or haemolytic-uraemic syndrome).2,3
ARF can be triggered by rhabdomyolysis and haemolysis, due to myoglobin and haemoglobin respectively, proteins that contain the “haemo” pigment which damages the kidney, causing tubular obstruction, acute tubular necrosis and vasoconstriction. Haemoglobin has a greater molecular weight (65 000Da) than myoglobin (17 000Da) and, in contrast, binds to proteins such as haptoglobin, making its filtration and excretion more difficult. Both cases presented dark-coloured urine, testing positive for blood in the urine test strip, and increase in plasma LDH levels. In myoglobinuria, the level of creatine-kinase enzyme increased and in the case of haemolysis, we detected anaemia, a decrease in haptoglobin and an increase of indirect bilirubin with the appearance of dysmorphic red blood cells in peripheral blood.4,5
Treating a rare blood-type is a complicated task because of the difficulty in finding blood of the same phenotype. Consequently, the options were to carry out cryopreservation of autologous red blood cells or to find compatible individuals within the patient’s family. In our case, blood from another hospital was reserved and blood from a family member was used.
Conflicts of interest
Lecture fees: Yes, but not related with the content of the published study.
Council Membership: The author (F.J. Gainza) is a member of the editorial committee of the magazine Nefrología and a reviewer of other international magazines.
Travel expenses: Not related to the content of the study. Routine funding for meetings and conferences organized by scientific societies.
