This systematic review elucidates the role of fingernail analysis in the diagnosis and management of diabetes mellitus (DM) and its complications. It combines multidisciplinary insights to highlight the potential of non-invasive diabetes assessment, long-term glucose monitoring, and early detection of complications. Covers a wide range of techniques, including spectroscopy and imaging methods such as near-infrared spectroscopy (NIR), Raman spectroscopy (RS), laser-induced breakdown spectroscopy (LIBS), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectroscopy (XRF), as well as microscopy and elemental analysis techniques such as dermoscopy, nail fold video capillaroscopy (NVC), inductively coupled plasma mass spectrometry (ICP-MS), and liquid chromatography-tandem mass spectrometry (LC-MS/MS), Nail biochemical analysis and Doppler ultrasound imaging were also included. Special emphasis is placed on glycemic biomarkers such as N-acetyl-DL-leucine enantiomers, carboxymethyl lysine (CML), and advanced glycation end-products (AGEs), which demonstrate robust diagnostic utility. Meta-analytical data indicate that these multimodal approaches yield Area Under the Curve (AUC) values of 0.78 e (CML), and advanced glycation end-products (AGEs), which demonstrate robust diagnostic utility. Meta-analytical data indicate that these multimodal approaches yield Area Under the Curve (AUC) values of from 0.78 to 0.88, underscoring their clinical potential for high sensitivity and specificity discrimination between diabetic and healthy populations Notwithstanding, challenges persist, including instrumentation costs, environmental interferences, and operator expertise requirements. Future directions prioritize elucidating the molecular mechanisms underlying nail-diabetes associations, innovating minimally invasive analytical platforms, and conducting multicenter validation trials to bridge the translational gap.