Delayed reactions to low-molecular weight heparins: Cross reactivity with unfractioned heparin.
Saturday, March 3, 2018
South Hall A2 (Convention Center)
Ana Rodriguez Fernandez, Patricia Rojas-Perez, Blanca Noguerado-Mellado

Heparins are anticoagulants used in thromboembolic disorders, which include unfractioned heparins (UH) and low-molecular weight heparins (LMWH). Cross reactivity between them is unknown.


A retrospective-descriptive study was registered in our Allergy Department including patients diagnosed of delayed hypersensitivity reactions to LMWH between January-2013 to March-2017.

Skin tests with LMWH and UH were performed, with readings at 48-96 hours.

When skin tests confirmed hypersensitivity mechanism, we performed a drug challenge test (DCT) with UH.


Twenty three patients were diagnosed of delayed reactions to heparin allergy. Eighteen (78,26%) women and five (21,73%) men with a 70,54 mean age (13,9 SD), 73 median. Clinical patterns were: erythematous local plaques 18 (78,26%) and 5 (21,73%) maculopapular exanthemas.

Twenty cases (86,95%) were due to hypersensitivity to enoxaparin and 3 (13,04%) to bemiparin. 78,26% patients were diagnosed by skin test, 13% by DCT and 8,69% by clinical history.

86, 66% of patients tolerated UH and 13,33% had a positive DCT with it. Cross-reactivity was 13, 33%. The negative predictive value for skin tests with enoxaparin was 88,88% and 66,66% for bemiparin.


Skin tests were diagnostic in 78, 26% of suspected hypersensitivity to LMWH.

Despite our short cases-serie, it seems that cross reactivity between LMWH and UH is low.

Skin tests and DCT with UH should be performed in all patients with allergy to LMWH.