Indian Journal of Pathology and Microbiology

: 2020  |  Volume : 63  |  Issue : 2  |  Page : 251--254

Management of transfusion needs in a case of immunizing anti-M antibody in a patient with acute myeloid leukemia

Anisha Navkudkar, Priti Desai, Rajesh Thakkar, Sunil Rajadhyaksha 
 Department of Transfusion Medicine, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai, India

Correspondence Address:
Priti Desai
Department of Transfusion Medicine, Tata Memorial Hospital, 5th Floor Service Block, Dr E Borges Road, Parel Mumbai - 400 012, Maharashtra


Anti-M is a relatively common “naturally occurring” antibody. Unexpected alloantibodies in patient's serum other than ABO isoagglutinins (e.g., anti-M) may cause a discrepancy in the reverse grouping. As long as anti-M does not react at 37°C, it is clinically insignificant for transfusion. However, we found this antibody to be of “immunizing” type which was reactive at 37°C and AHG phase and showing problems in blood grouping and crossmatch. This antibody had both IgM and IgG components. When “M” antibodies active at 37°C are encountered, antigen-negative or red cells that are compatible with an indirect antiglobulin test should be provided.

How to cite this article:
Navkudkar A, Desai P, Thakkar R, Rajadhyaksha S. Management of transfusion needs in a case of immunizing anti-M antibody in a patient with acute myeloid leukemia.Indian J Pathol Microbiol 2020;63:251-254

How to cite this URL:
Navkudkar A, Desai P, Thakkar R, Rajadhyaksha S. Management of transfusion needs in a case of immunizing anti-M antibody in a patient with acute myeloid leukemia. Indian J Pathol Microbiol [serial online] 2020 [cited 2020 Jul 12 ];63:251-254
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Full Text


Anti-M is a relatively common “naturally occurring” antibody.[1],[2],[3] Anti-M appears to be more common in children than in adults and is particularly common in patients with bacterial infections.[1] Although agglutinating anti-M may be considered as IgM, 50%–80% are IgG or have an additionally IgG component.[4] Very occasionally, anti-M has been implicated as the cause of acute and delayed Hemolytic transfusion reactions (HTRs), and anti-M has very rarely been responsible for severe Hemolytic Disease of Fetus and Newborn (HDFN).[5] As long as anti-M does not react at 37°C, it is considered as clinically insignificant. When anti-M reacts at 37°C, it is sufficient to provide units that are crossmatch-compatible at 37°C and at the antiglobulin phase.[6] We came across an “immunizing” anti-M antibody causing blood group discrepancy and incompatible crossmatch. Transfusion need was fulfilled by providing “M” antigen–negative crossmatch-compatible packed red cell unit.

 Case Detail

A blood sample of a 49-year-old female diagnosed with acute myeloid leukemia was received for blood grouping and antibody screening in the Department of Transfusion Medicine. Blood grouping and antibody screening were performed by column agglutination technique (CAT). Initial grouping results in [Table 1] show that there is an extra reaction with “A” cells in serum grouping. Also, antibody screen with three-cell panel was positive. A fresh sample was requested, and in the meantime, patient's history was enquired. Her historical blood group from other blood bank was “A” positive with antibody screen negative. The patient was married with two successful and uneventful pregnancies. She had received two units of packed red cells and three units of random donor platelets at another hospital. After excluding the possibility of technical error, further testing was used by conventional tube technique (CTT). To rule out the possibility of cold antibodies, the serum grouping was performed on a fresh sample by CTT at three different temperatures (4°C, room temperature, and 37°C), the results of which are shown in [Table 2]. We also used A1 lectin to rule out the possibility of a subgroup of A. The patient's red cells had a strong reaction with A1 lectin, so there was no possibility of a subgroup of A. Autocontrol and direct antiglobulin test were negative, ruling out the presence of autoantibody as shown in [Table 3]. Indirect antiglobulin test (IAT) by pooled O cells was positive. Grouping discrepancy was resolved at 37°C by pre-warm technique as shown in [Table 2]. Antibody screening was performed with 3-cell and 11-cell panels by CAT, the results of which corroborated with antibody screening by CTT [Figure 1] and [Figure 2]. Initially, on three-cell panel, probable antibodies identified were anti-e, anti-Fyb, and anti-M. Subsequently, antibody identification on 11-cell panel was carried out and antibody identified after crossing out was anti-M. Anti-M showed dosage effect with stronger reaction with homozygous cells (M+ N−) than cells (M+ +). On treatment of patient's serum with 2 mercaptoethanol (2-ME), the strength of reaction decreased from 2+ to 1+ showing the presence of IgG component to it. The patient's cells were phenotyped which showed the absence of M antigen.{Table 1}{Table 2}{Table 3}{Figure 1}{Figure 2}

To confirm the presence of antibodies, the following criteria were used:

  1. The three-cell rule (three cells positive with M antigen showing a positive reaction and three cells negative with M antigen showing a negative reaction).
  2. Cell numbers 2, 8, and 11 show 1+ to 2+ reactions due to a dosage effect.
  3. The patient is negative for M antigen.
  4. Presence of IgG component of anti-M antibody by treatment of serum with 2 ME.

With the help of the above criteria, we confirmed the presence of anti-M antibody. Blood group of the patient was confirmed as A positive with the presence of anti-M antibody. The antibody was reactive at 37°C and AHG phase, thus regarded as clinically significant. Only M antigen–negative crossmatched blood was provided for this patient with instructions of transfusion under warm conditions. Transfusion was uneventful.


There are approximately 36 recognized blood group systems, some of which are clinically very important. Of these, the ABO and Rh systems are used in routine practice for blood grouping. The MNS system (International Society of Blood Transfusion number 002)[7] is a highly complex system that has 46 antigens.[8] The common antigens in this system are M, N, S, and s. The prevalence of naturally occurring anti-M antibody detectable with saline-suspended cells at room temperature in blood donors is 1:2,500 with M+ N− cells and 1:5,000 with M+ N+ cells.[3],[9] Sometimes, cold alloantibodies like anti-M reactive with reverse grouping cells can lead to unexpected positive reactions.[6] A similar reaction was noticed in this case wherein anti-M interfered with A cells in the serum grouping which was resolved by performing blood grouping by pre-warm technique at 37°C. Generally, anti-M can be ignored in transfusion practice as they are not active at 37°C.[5] Many examples of anti-M are naturally occurring saline agglutinins that react below 37°C.[6] If room temperature incubation is eliminated from compatibility testing and screening for the antibody, these antibodies are not detected. When M antibodies active at 37°C are encountered, M antigen–negative or red cells that are compatible by IAT should be provided.[5],[10],[11] In the above case, the antibody detected was reactive at 37°C and AHG phase/IAT phase with partial IgG component and therefore can be considered of potential clinical significance. Hence, to rule out the possible reactivity observed at the IAT phase due to the presence of IgG and not the binding of IgM from the room temperature test phase, testing was conducted in strict warm conditions. M+ N− red cells tend to be strongly reactive with anti-M than are M+ N+ red cells. Antibodies that are weakly reactive may not be detected if they are treated with red cells expressing a single dose of antigen. This observable difference in strength of reaction based on homozygosity/heterozygosity for an allele is called “dosage effect,” which was observed in this case also. Although we may think of agglutinating anti-M as IgM, 50%–80% have an additionally IgG component.[4] They generally do not bind complement and they do not react with enzyme-treated red blood cells. Although the majority of anti-M antibodies are IgM antibodies and are noncomplement activating,[12] however, IgG component may coexist alone or in combination which may be complement activating. In this case, IgG component was confirmed by treating the serum with 2-ME. On treatment of serum with 2-ME, reaction with M antigen red cells still persisted indicating an IgG component of anti-M as only IgM could be destroyed by 2-ME. Cases of clinically significant anti-M antibodies have been reported by Das et al.[13] Two cases of anti-M were also reported by Tondon et al., one presenting as a blood group discrepancy and other as crossmatch incompatibility.[14] Anti-M antibodies are reported in cases of solid tumors by Soni et al.[15] However, no cases of anti-M in hematological malignancies have been reported in literature. Our case seems to be immune-mediated anti-M as the patient had a history of transfusion of packed red cells which could have led to the development of IgG anti-M. In this case, the grouping discrepancy was resolved by pre-warm technique. Also, M-negative unit was issued to this patient and transfusion was uneventful.


Anti-M is generally considered as a naturally occurring clinically insignificant antibody. Sometimes, its presence in the serum can pose problems in blood grouping and crossmatch. Blood grouping problem as we encountered was an extra reaction with A cells in serum grouping on CAT which was resolved by repeating the serum grouping by pre-warm technique after incubation at 37°C. For transfusion purposes, as long as anti-M antibody does not react at 37°C, it is sufficient to issue units that are crossmatch-compatible at 37°C in the IAT phase. But if the antibody reacts at 37°C, M antigen–negative blood should be provided for transfusion.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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