For decades, forensic scientists have sought a means of estimating the postmortem interval using laboratory analyses. The best known of these attempts uses a linear regression formula based on the increasing concentration of potassium ions in vitreous humor following death. Like all laboratory analyses, the determination of a potassium concentration is subject to pre-analytical, analytical, and post-analytical errors. Any error is magnified when entered into a regression formula that itself is subject to statistical variation, typically with a 95% confidence interval. Estimating the postmortem interval based solely on the concentration of potassium in vitreous humor proved too simplistic for accurate modeling of the myriad factors that influence postmortem changes. Research continues, using more complicated algorithms involving multivariate ion and chemical analyses and genomic sequencing of the postmortem biome. However refined estimates of the postmortem interval based on laboratory analysis become, sound medical practice will still require the integration of scene findings and information concerning the last time that a given decedent was known to be alive with the results of postmortem examination and laboratory analyses into a medical opinion concerning the postmortem interval.