Clinical relevance of silent red blood cell autoantibodies.

The diagnosis of autoimmune hemolytic anemia (AIHA) is based on the evidence of anemia, hemolysis and the detection of red blood cell (RBCs) autoantibodies. The absence of detectable RBC autoantibodies does not always exclude autoimmune hemolysis. Conversely, the presence of RBC autoantibodies is not always associated with hemolytic anemia. Silent RBC autoantibodies have been detected in healthy blood donors, in pregnant females and in patients with autoimmune disorders. While the occurrence of clinically non-significant RBC autoantibodies is a well-known phenomenon in immunohematology laboratories, there is little information about the clinical course of subjects with silent RBC autoantibodies and whether disorders known to be associated with AHIA could also be present in these subjects. To address these issues, we retrospectively analyzed the characteristics and the long-term outcome of 60 subjects with silent RBC autoantibodies who were referred to our Hematology Center between January 1995 and December 2012 and followed on a regular basis over time. Our results showed that the development of AHIA in subjects with silent RBC autoantibodies was a rare event and that disorders known to be associated with AHIA were present in a relevant proportion of cases with silent agglutinins. Subjects with silent RBC autoantibodies showed normal Hb values, no signs of hemolysis, acrocyanosis and/or Raynaud phenomena, and no previous history of drugs known to be associated with AHIA, vaccinations, infections, lymphoproliferative diseases or autoimmune disorders. The initial assessment included complete blood count, immunohematologic evaluation, reticulocyte count, haptoglobin, bilirubin, LDH, serum electrophoresis and clinical examination. Data on blood counts, bilirubin levels and immunohematologic tests performed during follow up were also recorded. More details about the clinical workout performed at baseline and during follow up are reported in the Online Supplementary data. Silent RBC autoantibodies were detected in 5 (8%) pregnant females, 34 (57%) healthy individuals (blood donors, 32; subjects with an abnormal agglutination of blood samples, 2) and 21 (35%) subjects screened prior to surgery (benign disorder, 16; malignancy, 5). The median follow up was 60 months (range, 10-204 months), the median age 48 years (range, 19-74 years), and the median Hb value 138.5 g/L (range, 124-167 g/L) with a median reticulocyte count of 74.5 x 10/L (range:11.580-186000). Four blood donors showed an increased reticulocyte count with Hb values ranging between 130 and 160 g/L. Haptoglobin, bilirubin, and LDH levels were normal in all cases (Table 1). IgG autoantibodies were detected in 24 (40%) cases, IgM in 35 (58%) and IgM+IgG in 1 (2%). Cold agglutinins with a median titer of 1:512 and a thermal amplitude around 30°C were recorded in 23/35 (66%) cases, and warm agglutinins in 12 (34%). The median number of immunohematologic tests per patient was 4 (range 213) (Table 2). Clinical and serologic characteristics of subjects with silent RBC autoantibodies according to the associated condition or disorder are described in Figure 1. Asymptomatic RBC autoantibodies were detected in 5 (8%) pregnant females at the time of the first trimester screening (IgG 3 cases, IgM 1, IgG+IgM 1) and persisted during and after pregnancy. No signs of hemolytic anemia were observed in either the mothers or the newborns. In 31 of the remaining 55 (56%) cases, no evidence of an underlying disorder was observed, while it was present in 24 (44%) cases; in 5 /21 (24%) with IgG autoantibodies and in 19/34 (56%) with IgM autoantibodies (P<0.05). Five (5/55, 9%) cancer-bearing subjects (breast cancer 2; thyroid cancer, 3) revealed silent RBC autoantibodies (IgG, 2; IgM, 3) at the time of the pre-surgery screening for cancer removal. RBC autoantibodies disappeared in 2 cases (IgG 1; IgM 1) after removal of thyroid cancer, while they persisted in 3 with active disease. The significant positivity of other autoantibodies directed further serologic and clinical evaluations allow-