Objectives It is unknown to what extent the fluid retention (FR) status disrupts the detection of weight loss rate (WLR) in adult patients with advanced cancer. This study aimed to determine the association of FR status with WLR.

Methods This study was a secondary analysis of a prospective cohort study. FR was evaluated as follows: oedema (0, no; 1, yes), pleural effusion (0, no; 1, yes but asymptomatic; 2, symptomatic) and ascites (0, no; 1, yes but asymptomatic; 2, symptomatic). Patients were divided into three groups according to their FR scores: no-FR (0), moderate-FR (1–2) and high-FR (3–5). Multiple regression analysis was performed.

Results Four hundred and twenty patients were categorised: no-FR group (n=164), moderate-FR group (n=158) and high-FR group (n=98). The prevalence of oedema, pleural effusion and ascites was 63.9%, 27.8% and 36.7% in the moderate-FR group, and 93.9%, 61.3% and 82.6% in high-FR group. The means of WLR were 9.2, 8.4 and 3.8 in the groups. The high-FR group and the FR score of 5 were correlated with WLR (estimate −4.71, 95% CI −7.84 to –1.58; estimate −10.29, 95% CI −17.84 to –2.74).

Conclusions The coexistence of FR was significantly correlated with WLR.