Electrolyte Concentration Differences Between Left and Right Vitreous Humour Samples

Abstract

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.

Comparative study of two vitreous humor sampling methods in rabbits

“…In contrast, the ratios of the cases with variations 15 % greater the mean values in the group B (for the first time samples) are 0/9, 0/9, 1/9, 0/9 and 2/9, respectively. Interestingly, our results are consistent with other reports in which entire-sampling showed obvious variations [2][3][4] and micro-sampling yielded less variations [5,6] . This suggests that the micro-sampling methodology is more reliable than one-time entire sampling, and can yield consistent results.…”

“…Some researchers [2][3][4] believe that there exists a significant difference in electrolyte concentrations between the two eyes. In contrast, several other reports [5,6] suggested that the two-eye variations are acceptable and they believed that the humor of either eye is representative of the individual.…”

Vitreous Humor: A Short Review on Post-mortem Applications

“…Post-mortem vitreous BHB is a useful marker for DKA when levels are elevated and accompanied by an above threshold vitreous glucose level concentration [62]. The argument for the higher thresholds are because the median ketone levels in blood are generally over 5 mmol/L in patients with diabetic ketoacidosis [86,87] and blood ketone levels correlate with VH ketone concentrations [71,73,83,86,87].…”

Sudden adult death

“…During life there is equilibration of electrolytes with the blood, however, after death, changes in electrolyte levels occur due to necrosis of the retinal cells [457][458][459]. Caution also has to be observed due to difference between the eyes having been observed by some [458,460], but not by others [461]; variation may result from the different methods of analysis [462]. Synovial fluid [463,464], pericardial fluid [465,466] and cerebrospinal fluid (CSF) [463,467] have also been studied as possible sources of fluid for biochemical analysis.…”