[Clinical and Laboratory Characteristics of Primary Autoimmune Hemolytic Anemia Patients with Negative Results of DAT by Tube Test But Positive Results by Microcolumn Gel Assay].

Objective: To investigate the clinical features and laboratory characteristics of primary autoimmune hemolytic anemia (AIHA) patients with negative results of direct antiglobulin test (DAT) by tube test but positive results by microcolumn gel assay, in order to provide references for the diagnosis of these patients.

Methods: 59 patients diagnosed with primary AIHA in our hospital from January 2015 to December 2020 were retrospectively analyzed. According to the results of tube test and microcolumn gel assay, the cases were divided into 3 groups, and the clinical and laboratory characteristics of each group were compared.

Results: The cases were grouped as follows: Group I, cases with negative results by both methods of DAT (n=5); Group II, cases with negative results by tube test but positive results by microcolumn gel assay (n=26); Group III, cases with positive results by both methods of DAT (n=28). There was no significant difference in age and sex between Group II and other groups, whereas the positive rate of anti-IgG + anti-C3d of Group II was lower than that in Group III (P=0.015). The main clinical manifestations of Group II were chest tightness, shortness of breath, fatigue, as well as yellow skin and sclera or dark urine, but the incidence rate of these symptoms was not significantly different from other groups. Anemia related indexes in Group II such as red blood cell (RBC) count and hemoglobin (Hb) were lower than the reference intervals, but there was no significant difference compared with other groups. Hemolysis related indexes in Group II such as reticulocyte (Ret) ratio, indirect bilirubin (IBIL), lactate dehydrogenase (LDH) and free-hemoglobin (F-Hb) were higher than the reference intervals, and the latter two items were signficantly higher than those in Group I (P=0.031 and P=0.036). Serum complement C3 and C4 in Group II were higher than those in Group III (P=0.010 and P=0.037).

Conclusion: Anemia severity of primary AIHA patients who were negative of DAT by tube test but positive by microcolumn gel assay was similar to those with negative or positive results by both DAT methods, but the mechanism and degree of complement system involved in hemolysis might be different. Results above may be helpful for laboratory diagnosis of this kind of patients.