Aim: Comparative evaluation of ultraviolet–visible (UV–Vis) spectroscopy and Congo red card-based test in the diagnosis of preeclampsia. Materials and methods: In this case–control study, UV–Vis spectroscopy and Congo red card test were done using mid-stream clean catch urine samples collected from 98 cases and 98 controls. The results obtained were used to calculate the specificity and sensitivity of each test. Results: Out of 98 cases, 76 showed increased absorbance in UV–Vis spectroscopy while 69 showed Congo red positivity. Thus, the ultraviolet (UV)-absorbance method was found to be more sensitive (77.53) and specific (80.61) compared to the Congo red paper-based test (sensitivity, 70.40; specificity, 64.28) in the detection of the misfolded proteins present in the urine samples of the preeclamptic patients. Conclusion: The UV–Vis absorption spectroscopy is a renowned yet innovative technique in the diagnosis of preeclampsia. It is more sensitive and specific to the existing Congo red paper-based test. Clinical significance: Several studies show that urine of preeclampsia patients shows the presence of misfolded proteins which are present about 2 weeks before the onset of symptoms, that is, clinical diagnosis. This creates scope for early detection and diagnosis of preeclampsia. In this study, we establish the role of spectroscopy as a novel test in diagnosing misfolded proteins in preeclamptic patients and compare its diagnostic performance to the highly acclaimed Congo red card test.