Positive direct antiglobulin test result in dialysis patients resulting from antiformaldehyde antibodies

Patients on chronic hemodialysis who are treated with reusable dialyzers sterilized with formaldehyde are known to have antibodies develop with N-like specificity. These sera have been shown to also react with formaldehyde-treated N-negative cells. This latter specificity has been referred to as antiformaldehyde (anti-Form). Because anti-Form develops presumably in response to formaldehyde-treated cells that gain access to the patient's circulation, the authors reasoned that recipient anti-Form once established might be capable of binding to cells exposed to formaldehyde during dialysis, resulting in a positive direct antiglobulin test (DAT) result and an eluate reacting only with formaldehyde-treated reagent cells. The authors studied 96 patients on chronic hemodialysis who were exposed to formaldehyde-sterilized equipment. Both anti-N-like and anti-Form specificities were found. Anti-Form was detected in the serum of 16% of patients when tested against 0.37% (w/v) formaldehyde-treated cells. Nineteen percent of patients demonstrated a positive DAT result. The presence of a positive DAT result was significantly associated with the presence of anti-Form in the patient's serum (P less than 0.05). Red blood cell eluates from two patients with a positive IgG DAT result and serum anti-Form demonstrated anti-Form in the eluate. Increasing the concentration of formaldehyde treatment of red blood cells resulted in increasing strength of reactions with anti-Form serum, suggesting that the sensitivity of serum and eluate testing could be modified by the method of cell preparation. As expected, the reactivity of anti-Form with formaldehyde-treated cells could not be neutralized by formaldehyde. The authors conclude that patients treated with formaldehyde-sterilized reusable dialysis equipment may on occasion have a positive DAT result and have an eluate that is nonreactive with the use of standard reagent cells but reactive with formaldehyde-treated cells.