title: Improved estimation of postmortem interval based on differential behaviour of vitreous potassium and hypoxantine in death by hanging.
abstract: Many formulae are available to estimate the relation between the potassium ([K+]) and hypoxantine ([Hx]) concentration in the vitreous humour and the postmortem interval (PMI). Typically these have been based on a correlation test and linear regression using the postmortal interval as the independent variable and [K+] or [Hx] as the dependent variable in order to estimate the confidence interval. However, a recent study has shown that a more precise measurement of PMI can be obtained if [K+] is used as the independent variable. The regression lines obtained from the most recent deceased subjects with forensic relevance received for autopsy in the Institute of Legal Medicine are [K+] = 5.589 + 0.174PMI and [Hx] = 26.459 + 3.017PMI, by changing the variables, we obtain PMI=3.967[K+] - 19.186 (R2 = 0.688, P < 0.001) and PMI = 0.172 [Hx] + 0.170 (R2 = 0.518, P < 0.001). In this paper we propose the cause of death as an extra factor which modifies the relationship and gives even greater precision in estimating PMI. In cases of death by hanging the results are considerably improved with [K+] = 5.224 + 0.225PMI and [Hx] = 15.161+4.957PMI, respectively, and consequently, PMI = 3.631[K+] - 17.334 (R2 = 0.818, P< 0.001) and PMI = 0.153[Hx] - 0.368 (R2 = 0.757, P < 0.001): the slope is less and the precision is obviously enhanced.
authors.affiliation: Institute of Legal Medicine, School of Medicine, C/San Francisco s/n, University of Santiago de Compostela, 15782 Galicia, Spain. barusiml@usc.es
authors.forename: José I
authors.initials: JI
authors.lastname: Muñoz Barús
authors.forename: JoséM
authors.initials: J
authors.lastname: Suárez-Peñaranda
authors.forename: Xosé L
authors.initials: XL
authors.lastname: Otero
authors.forename: María S
authors.initials: MS
authors.lastname: Rodríguez-Calvo
authors.forename: Eduardo
authors.initials: E
authors.lastname: Costas
authors.forename: Xoán
authors.initials: X
authors.lastname: Miguéns
authors.forename: Luis
authors.initials: L
authors.lastname: Concheiro
mesh_terms: D001237:Asphyxia / Q000378:metabolism*; D001344:Autopsy; D003404:Creatinine / Q000032:analysis; D005260:Female; D005554:Forensic Medicine / Q000379:methods; D006801:Humans; D019271:Hypoxanthine / Q000032:analysis*; D008297:Male; D011180:Postmortem Changes; D011188:Potassium / Q000032:analysis*; D012680:Sensitivity and Specificity; D013997:Time Factors; D014508:Urea / Q000032:analysis; D014822:Vitreous Body / Q000737:chemistry*
chemical_list: D019271:Hypoxanthine; D014508:Urea; D003404:Creatinine; D011188:Potassium