The role of the Coombs test in evaluating hemolysis in adults

Dear Editor,

The article by J M Zaradona and Mark H Yazer on the clinical utility of Coombs test merits consideration of the pit-falls of a negative result [1]. A negative Coombs test in a patient with clinically significant hemolysis requires further evaluation. Reasons for a negative DAT may be due to low-affinity antibodies coating the red cell surface which are removed in the washing process or the prior use of corticosteroid therapy in the patient. IgG antibodies and C3d are detected by the direct antiglobulin test (DAT); however, IgM and particularly IgA antibodies may not necessarily be detected by the polyclonal antihuman-globulin serum. Therefore, DAT using anti-IgA or anti-IgM may be required if a negative DAT using anti-IgG do not correlate with clinical manifestations. Patients whose RBCs are coated with multiple immunoglobulins have severe hemolysis and may need intensive therapy with immunosuppressive agents [2] or even splenectomy [3].

A major immunohaematology referral center in UK found 124 of 5235 patients had warm elutable IgA antibodies and of these, six had only IgA autoantibodies coating the red cells [4]. It is known that IgA complexes can activate the alternative pathway and result in complement activation. Therefore, measurement of complement components C3 and C4 could prove useful in some situations. Splenic sequestration of IgA- sensitized red cells occur and in-vitro analysis have shown monocytes to be involved in haemolysis of the sensitized red cells [5]. Naturally occurring antibodies are of IgM isotype which binds complement and autoantibodies of this class occur in conjunction with anti-IgG and or anti-IgA immunoglobulins. In- vivo autoagglutination of IgM antibodies can lead to multi-organ failure and usually have a high rate of mortality [6]. Sokol RJ and colleagues reported two patients with only IgM autoantibody having chronic hemolysis and one required splenectomy [7]. It is therefore important that clinicians are aware of the limitations of biological tests and investigate a ‘negative-Coombs test’ patient with severe hemolysis and organ involvement in greater detail.

Competing interests: None declared.

1. Zarandona JM, Yazer MH. The role of the Coombs test in evaluating hemolysis in adults. CMAJ. 2006 Jan 31;174(3):305-7.

2. Sokol RJ, Booker DJ, Stamps R, Booth JR. Autoimmune hemolytic anemia due to IgA class autoantibodies. Immunohematol. 1996;12(1):14-9.

3. Bardill B, Mengis C, Tschopp M, Wuillemin WA. Severe IgA-mediated auto- immune haemolytic anaemia in a 48-yr-old woman. Eur J Haematol. 2003 Jan;70(1):60-3.

4. Sokol RJ, Booker DJ, Stamps R, Booth JR, Hook V. IgA red cell autoantibodies and autoimmune hemolysis. Transfusion. 1997 Feb;37(2):175- 81.

5. Clark DA, Dessypris EN, Jenkins DE Jr, Krantz SB. Acquired immune hemolytic anemia associated with IgA erythrocyte coating: investigation of hemolytic mechanisms. Blood. 1984 Nov;64(5):1000-5.

6. Friedmann AM, King KE, Shirey RS, Resar LM, Casella JF. Fatal autoimmune hemolytic anemia in a child due to warm-reactive immunoglobulin M antibody. J Pediatr Hematol Oncol. 1998 Sep-Oct;20(5):502-5.

7. Sokol RJ, Booker DJ, Stamps R, Sobolewski S, Haynes AP. Autoimmune hemolytic anemia caused by warm-reacting IgM-class antibodies. Immunohematol. 1998;14(2):53-8.

Conflict of Interest:

None declared