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:As another well-known difference in clinical presentation between patients with HSH and FHHNC, serum PTH levels are inappropriately suppressed (<3 pg/mL) or below normal (5–12 pg/mL) in HSH patients during phases of severe hypomagnesaemia, whereas they are usually elevated in patients with FHHNC [2], which can also be seen in our cohort.
Category: