The time interval since death can be estimated by measuring potassium in the vitreous humor.
Conditions for study group:
(1) time interval since death: 3 to 120 hours
(2) ambient temperature < 50°F
(3) sudden death from traumatic or natural causes
Screen for underlying metabolic disorders:
(1) Sodium, calcium, chloride, urea and nitrogen are stable in the post-mortem interval up to 120 hours postmortem.
(2) The presence of an underlying metabolic disorder will result in increased levels in the vitreous humor before death, making post-mortem time estimates falsely high.
(3) The proposed limits on use of potassium equations:
(3a) urea nitrogen: < 70 mg/dL or < 100 mg/dL
(3b) creatinine < 1.0 mg/dL
Madea Formula
hours post-mortem =
= (5.26 * (potassium concentration of vitreous humor in mEq/L)) - 30.9
with 95% confidence interval +/- 19 hours
Sturner Formula
hours post-mortem =
= (7.14 * (potassium concentration of vitreous humor in mEq/L)) - 39.1
with 95% confidence interval +/- 33 hours
Interpretation:
• Sturner formula tends to overestimate the time since death, due to lesser slope
• using the screen of < 100 mg/dL for urea nitrogen is sufficient to exclude significant antemortem metabolic disorders, but using urea nitrogen < 70 mg/dL and creatinine < 1.0 mg/dL narrowed the confidence interval (+/- 15 hours)
Limitations:
• Pre-existing metabolic disorders can result in falsely elevated time intervals.
