Which elements on a standard cmp or other test could suggest dehydration?

Multiple: On a CMP, a high BUN-to-creatinine ratio MAY be suggestive of dehydration. On a review of urine electrolytes, a low urine chloride or a low FENa may also suggest this. But the operative word is SUGGEST, as there are many causes of a high BUN:Cr and low FENa. To actually put context to these labs, it is always advisable to seek your physician to interpret them properly and apply them to your case.

Na, BUN, Creat: The three most important components on a comprehensive metabolic panel with respect to "hydration" are the Sodium or Na (This will be elevated with dehydration), The Blood Urea Nitrogen or BUN (This too will be elevated with dehydration) and the Creatinine or Creat. In severe cases of dehydration, the creat can be elevated signifying kidney damage.