Osmolality and Other Chemical Determinations in Postmortem Human Vitreous Humor

The measurement of osmotic pressure in blood and urine has been used extensively in clinical investigation and is beginning to be available as a diagnostic test in the hospital laboratory [1–4]. It is dependent on the number of solute particles in solution, rather than their shape, weight, or charge. The determination of the freezing point depression of a solution gives a good estimate of the number of particles and is the basis for the calculation of the osmolality. Serum osmolality has a normal range of 275 to 295 mOsm/kg, with electrolytes, particularly sodium, contributing over 90 percent of this value. Glucose, nonprotein nitrogen, and protein substances make up a large portion of the remainder. The average osmolality of urine ranges from 300 to 1090 mOsm/kg, varies with dietary intake, and is generally higher in males [3]. The mean value for cerebrospinal fluid osmolality in fifty living patients was found to be 281 mOsm/kg, and the range of values extended from 269 to 304 mOsm/kg [5]. Postmortem spinal fluid studies to date have not included osmolality determinations.