Hemolysis and IgA‐antibodies against tissue transglutaminase: When are antibody test results no longer reliable?

Background Antibodies against tissue transglutaminase (TTG) of isotype IgA (IgA‐aTTG) represent reliable diagnostic markers to confirm or exclude celiac disease (CD). Hemolysis (HL) is an important pre‐analytical factor. HL can be quantified as HL index (HI) correlating with the concentration of free hemoglobin. TTG is abundant in erythrocytes and released upon HL. In immunoassays, the released TTG may interfere with binding of IgA‐aTTG to the coated TTG. Methods We selected 17 HL‐free sera from children with biopsy‐confirmed CD: 7 with low‐positive (1‐5 multiples of upper limit of normal [×ULN]), 5 with intermediate (5‐10 × ULN) and 5 with high IgA‐aTTG (10‐15 × ULN). Sera were spiked with hemolysates resulting in HIs ranging from 12.5 to 800 (12.5‐800 mg/dL free hemoglobin). Results IgA‐aTTG values were significantly decreased (>10%) after addition of hemolysates even if HL was invisible (HI