OBJECTIVE: Protein loss from wound fluid is usually recognized as one of the factors contributing to the deterioration of the nutritional status in older patients with severe pressure ulcers. We quantified the protein loss owing to pressure ulcers and investigated associations with wound-related factors and nutritional status. METHODS: This cross-sectional study included 25 patients (>or=60 y) from 10 institutions, with full-thickness pressure ulcers. Wound fluid was collected once after accumulating beneath a film dressing. The amount of protein loss per day was estimated by the volume of wound fluid per hour and the total protein concentration in the wound fluid. Wound evaluations and nutritional assessments were performed. Correlations between variables were obtained using Spearman's rank correlation. RESULTS: The median age of the patients was 79 y (range 61-100), and median body mass index was 19.6 kg/m(2) (12.2-24.9). The median amount of protein loss was 0.2g/d (0.04-2.1), which corresponded to 0.01 g x kg(-1) x d(-1) (<0.01-0.04) and 0.6% (0.1-13.8) of protein intake. Four wounds characterized as infected or surgically debrided lost 1.5-2.1g of protein per day, which was substantially higher than other wounds lost. Protein loss was correlated with wound severity including area, depth, the wound severity score, and infectious markers (all Ps<0.05), but not with body mass index or arm muscle circumference (P>0.05). CONCLUSION: The amount of protein loss could be small and thus may not be related directly to nutritional status, although it increased as the wound became more severe.