Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In patients with insulin resistance, production of NH3 from proximal tubules is reduced and ammonia excretion is also reduced accordingly, resulting in low urine pH.[27] In addition, in patients with insulin resistance, sodium absorption is increased because of hyperinsulinemia, which also lowers urine pH.
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