A young woman developed a line-associated deep vein thrombosis (DVT), which was treated with low molecular weight heparin (dalteparin). 8 days later, the DVT had significantly extended-in spite of therapeutic heparin levels. A diagnosis of heparin-induced thrombocytopenia and thrombosis (HITT) was considered, but the platelet count had not dropped. Nevertheless, a HITT assay was carried out which came back positive, with a repeat assay confirming the result. Dalteparin was stopped and apixaban treatment started, with symptomatic recovery over the following days and weeks.