p53-upregulated modulator of apoptosis (PUMA) is a biomarker associated with islet cell health. If PUMA is low, islet cells are typically healthy. If PUMA is high, islet cells are typically unhealthy or dying. PUMA may be measured by either measuring its nucleic or amino acid. PUMA mRNA may be induced by TNF-α stimulation in a time- and dose-dependent manner and β cell apoptosis is induced through a mitochondrial pathway. TNF-α significantly inhibited glucose-induced preproinsulin precursor mRNA synthesis. Such β cell stress signaling in human islets indicates overall state of islet health and, ultimately, the risk of onset and/or degree of severity of both type 1 and type 2 diabetes mellitus.