Potassium in vitreous humour
Background
Potassium was one of the first biochemical markers to be used for estimation of time of death. It is dependent on the ambient temperature, and this should be corrected for when estimating the post mortem interval.
Important publications of note:
- Rognum et al 2016. Estimation of time since death by vitreous humor hypoxanthine, potassium, and ambient temperature. Forensic Sci. Int. 262, 160–165
- Zilg, B., Bernard, S., Alkass, K., Berg, S., Druid, H., Lyon, C.B., Umr, C., Jordan, I.C., 2015. A new model for the estimation of time of death from vitreous potassium levels corrected for age and temperature. Forensic Sci. Int. 254, 158–166.
Method
Eye fluid (vitreous humour) is a clear gel that fills the space between the lens and the retina of the eye. It is an easily available and less complex fluid (contains less interfering components) than for example blood. This makes it a good object of analysis.
Accuracy and use
Both the hypoxanthine and the potassium method may be used for a longer period of time after death (4 days) than methods based on temperature drop (1 day). Moreover the hypoxanthine method is substantially more precise than the classical methods currently used.
Precautions
A problem with this method is that the level of potassium varies between healthy individuals when alive (3,5 – 5,0 mmol/l). Loss of kidney function, low intake of fluid and the use of diuretics can give rise to further aberration.
Also when using this method it is of importance to consider ambient temperature.