Gastrointestinal (GI) nematode infections are a significant health and welfare threat to calves in pasture-based rearing systems. Sustainable control requires an efficient and cost-effective diagnostic tool. The serum pepsinogen assay is a long-established tool to monitor the infection level. However, the relatively high cost and lack of standardisation hinder the broad implementation of this method. Here, the more cost-efficient and robust Ostertagia ostertagi-Ab ELISA is evaluated as a potential alternative diagnostic method in first-season grazing (FSG) calves. We performed both a literature review of studies where this method has been applied in FSG calves and conducted field studies in Belgium and Sweden to compare results from the O. ostertagi-Ab ELISA with the serum pepsinogen assay. We conclude that the O. ostertagi-Ab ELISA test is a valuable monitoring tool in FSG calves and could complement or replace the serum pepsinogen assay.