Background: Accurate first-line diagnostics are essential for early recognition of cancer but also to identify patients free of disease. The biomarker soluble urokinase plasminogen activator receptor (suPAR) is elevated in patients with cancer or non-malignant disease compared to disease-free patients. We tested if low suPAR could be used to identify disease-free patients in an accelerated cancer diagnostics program, including ruling out cancer. Methods: Patients with serious nonspecific symptoms and signs of cancer (NSSC) were included at the Diagnostic Outpatient Clinic, Copenhagen University Hospital Hvidovre, Denmark. Data from a clinical examination, including blood tests and imaging, was combined with national registry data on diagnoses and mortality. The association between blood suPAR and the primary outcome of disease-free (i.e., absence of incident disease and mortality) within 1-year follow-up was analysed with logistic regression analysis. Results: Of 1583 patients included, 349 (22.0%) were diagnosed with cancer, 837 (52.9%) with non-malignant disease, and 392 (25.8%) were disease-free within one year. Admission suPAR was significantly lower in disease-free patients compared to patients with cancer or non-malignant disease (P < 0.001), area under the curve 0.67 (95% confidence interval (CI): 0.64–0.70). The highest positive predictive value (PPV) for the outcome of disease-free was 0.55 (95% CI: 0.41–0.68) at a suPAR of 1.65 ng/mL. Patients who died had significantly higher suPAR compared to patients who survived in all disease subgroups. The AUC of suPAR for 1-year mortality was 0.80 (95% CI: 0.77–0.83). Conclusions: suPAR was significantly lower in disease-free individuals compared to patients with cancer or other conditions, but the PPV was not sufficiently high to terminate further clinical investigation with appropriate safety. Elevated suPAR may be a useful prognostic marker for adverse outcomes.