ABG or VBG
BMP, phos, mag
Urine pH
Urine electrolytes - Na, K, Cl, Ca, Cr
Plasma aldosterone and cortisol for type IV<unk> 
Note that when hyperkalemia is present, aldosterone should be elevated, so a "normal" aldosterone level may be relatively low
Renal tubular acidosis
See metabolic acidosis
Dialysis-associated hypotension
Anion gap acidosis
Dehydration
Dehydration 
Hyperosmolar hyperglycemic state
Dialysis disequilibrium syndrome