Methods and therapeutics for treating nitric oxide (NO) mediated condition comprising administering a therapeutically effective amount of a pharmaceutical composition containing a therapeutic, wherein the therapeutic one of increases xanthine oxidase (XO) associated nitrite conversion to nitric oxide and increases nitrite conversion to nitric oxide via DADS. Method and devices for measuring an amount of nitrite in a sample comprising obtaining a sample, adding diallyl disulfide (DADS) to the sample, measuring a post DADS amount of nitric oxide (NO) in the sample, and using the post DADS amount of NO in the sample to determine the amount of nitrite in the sample. Methods and therapeutics for diagnosing and treating critical limb ischemia (CLI) versus non-critical limb ischemic peripheral artery disease (PAD) in a patient comprising determining a patient indicator value, where the patient indicator is value one of a total hydrogen sulfide metabolite plasma level, a total nitric oxide, nitrite, and nitrite (NOx) plasma level, a ratio of free hydrogen sulfide plasma level to total NOx plasma level, and a ratio of total hydrogen sulfide metabolite plasma level and total NOx plasma level, diagnosing the patient with as having CLI based on the patient indicator value, and administering to the patient a therapeutic for CLI.