2 mL (1.5 mL min.) Serum from 1 SST AND 5 mL (3 mL min.) aliquot of random Urine. Do not use preservative. Separate serum within 1 hour of collection. Ship refrigerated. DO NOT FREEZE.
Freezing point depression
Sample Daily by 3 pm; Report Same day
The ratio between urine and serum osmolality helps in the differential diagnosis of Polyuria.