Electrolyte concentration differences between left and right vitreous humor samples.
Between-eye differences in electrolyte concentrations were studied in 200 medico-legal autopsies using an ion-specific electrode system. Taking the highest of the paired vitreous potassium concentrations, cases < 15 mM/L were classified as biochemically nonputrefied (Cat.1, n = 124), cases 15 to 20 mM/L as early putrefaction (Cat.2, n = 51), and cases > 20 mM/L as biochemically putrefied (Cat.3, n = 25). Mean paired vitreous sodium for all cases (n = 200) was 112 to 173 mM/L (mean 148, standard deviation (SD) = 8.9); between-eye differences were 0 to 8 mM/L (0% to 5.1% of mean), averaging 1.5 mM/L (1%) and with only one case (in Cat.3) outside instrument accuracy (+/- 3 mM/L). Mean paired vitreous chloride for all cases was 73 to 124 mM/L (mean 109, SD = 7.8); between-eye differences were 0 to 9 mM/L (0% to 8.8% of mean), averaging 1.7 mM/L (1.5%) and with 5 of 200 cases outside instrument accuracy (+/- 3 mM/L). Thus between-eye concentration differences of sodium and chloride are tolerable using this methodology. Previous reports of greater variability likely reflect errors introduced by sample manipulation prior to analysis. By contrast, between-eye differences in potassium in Cat.1 cases were 0 to 2.34 mM/L (0% to 21.8% of mean) averaging 0.37 mM/L (3.3%). Significant and erratic between-eye differences in potassium undermine the usefulness of vitreous potassium in estimation of time of death.