Estimation of postmortem interval using thanatochemistry and postmortem changes

Available online 25 September 2012

Peer review under responsibility of Alexandria University Faculty of Medicine.

Figures & data

Table 1 Scores for the development of the three postmortem changes (rigidity, hypostasis and corneal turbidity).¹⁰

Score	Rigidity	Hypostasis	Corneal turbidity
1	Before onset	Before appearance	No clouding
2	Partial development	Easy to remove by thumb pressure	Slight clouding
3	Complete development	Hard to remove by thumb pressure	Moderate clouding
4	Partial resolution	Unable to remove by thumb pressure	Strong clouding
5	Complete resolution	–	–

Table 2 Distribution of autopsy cases according to different ranges of postmortem interval (PMI) (n = 70).

PMI group (h)	Autopsy cases		PMI, Mean ± SD
	No.	%
Group I, 0–	12	17.1	8.83 ± 0.39
Group II, 12–	16	22.9	20.81 ± 2.37
Group III, 24–60	42	60.0	31.31 ± 9.76
Total	70	100
Min–Max	8–60
Mean ± SD	24.99 ± 11.54

Table 3 Relation between different scores of hypostasis and PMI (n = 70).

Hypostasis score	PMI (h)						Total
	Group I, 0–		Group II, 12–		Group III, 24–60
	No.	%	No.	%	No.	%	No.	%
Score 1	0	–	0	–	0	–	0	–
Score 2	0	–	0	–	0	–	0	–
Score 3	10	83.3	0	–	0	–	10	14.3
Score 4	2	16.7	16	100	42	100	60	85.7
Total	12	100	16	100	42	100	70	100
χ^2	56.39
p value	<0.0001^*

* Statistically significant at p ⩽ 0.05.

Table 4 Relation between different scores of rigidity and PMI (n = 70).

Postmortem rigidity score	PMI (h)						Total
	Group I, 0–		Group II, 12–		Group III, 24–60
	No.	%	No.	%	No.	%	No.	%
Score 1	0	–	0	–	0	–	0	–
Score 2	0	–	0	–	0	–	0	–
Score 3	2	16.7	9	56.3	7	16.7	18	25.7
Score 4	10	83.3	6	37.5	20	47.7	36	51.4
Score 5	0	–	1	6.2	15	35.6	16	22.9
Total	12	100	16	100	42	100	70	100
χ^2	18.33
p	0.001^*

* Statistically significant at p ⩽ 0.05.

Table 5 Relation between different scores of corneal turbidity and PMI (n = 70).

Corneal turbidity scores	PMI						Total
	Group I, 0–		Group II, 12–		Group III, 24–60
	No.	%	No.	%	No.	%	No.	%
Score 1	10	83.3	0	–	1	2.4	11	15.7
Score 2	2	16.6	13	81.3	12	28.6	27	38.6
Score 3	0	–	2	12.5	13	30.9	15	21.4
Score 4	0	–	1	6.2	16	38.1	17	24.3
Total	12	100	16	100	42	100	70	100
χ^2	65.62
p value	<0.0001^*

* Statistically significant at p ⩽ 0.05.

Table 6 Correlation between PMI and scores of postmortem rigidity, hypostasis and corneal turbidity.

Spearman's rho correlation	Postmortem scoring
	Hypostasis	Rigidity	Corneal turbidity
r	0.57	0.40	0.81
p value	<0.0001^*	0.001^*	<0.0001^*

* Statistically significant at p ⩽ 0.05.

Table 7 Relation between K⁺ concentration in VH and PMI (n = 70).

PMI	K^+ level (mmol/l)
	Min	Max	Mean ± SD
0–	6.40	12.00	8.40 ± 1.65
12–	6.50	13.40	9.51 ± 2.29
24–60	5.30	18.90	11.63 ± 3.04
F-test	6.01
p	0.004^*

* Statistically significant at p ⩽ 0.05.

Figure 1 Scatter plot for the relationship between K⁺ concentration in VH and PMI with 95% confidence intervals (n = 70).

Table 8 Relation between Hx concentration in VH and PMI (n = 70).

PMI	Hx level (μmol/l)
	Min	Max	Mean ± SD
0–	97.00	206.00	151.92 ± 34.89
12–	60.00	460.00	234.75 ± 147.23
24–60	60.00	680.00	315.76 ± 134.24
F-test	7.03
p	0.002^*

* Statistically significant at p ⩽ 0.05.

Figure 2 Scatter plot for the relationship between Hx concentration in VH and PMI with 95% confidence intervals (n = 70).

Table 9 Regression equations obtained for prediction of PMI.

	Equation	R^2	p
1	PMI = 1.377K^+ + 9.050	0.37	<0.0001^*
2	PMI = 0.027Hx + 15.401	0.207	0.001^*
3	PMI = 0.978K^+ + 0.014 Hx + 9.178	0.285	<0.001^*
4	PMI = 2.02 rigidity + 6.31 hypostasis + 6.94 corneal turbidity − 24.94	0.717	<0.001^*
5	PMI = 0.667K^+ + 0.003Hx − 0.191 rigidity + 4.907 hypostasis + 4.68 corneal turbidity − 13.624	0.78	<0.001^*

* Statistically significant at p ⩽ 0.05.

Table 10 Regression equations obtained for prediction of PMI with their adjusted R² values and percent of shrinkage.

	Equation	R^2	p	Adjusted R^2	% Shrinkage
1	PMI = 1.377K^+ + 9.050	0.37	<0.0001^*	0.335	3.5
2	PMI = 0.027Hx + 15.401	0.207	0.001^*	0.17	3.7
3	PMI = 0.978K^+ + 0.014Hx + 9.178	0.285	<0.001^*	0.228	5.7
4	PMI = 2.02 rigidity + 6.31 hypostasis + 6.94 corneal turbidity − 24.94	0.717	<0.001^*	0.685	3.2
5	PMI = 0.667K^+ + 0.003Hx − 0.191 rigidity + 4.907 hypostasis + 4.68 corneal turbidity − 13.624	0.78	0.001^*	0.75	3

* Statistically significant at p ⩽ 0.05.

Figure 3 The mean values and the 95% confidence intervals of the absolute deviations for the residuals of the five equations. • 95% CI: 95% confidence interval. • Abs K: Absolute residual obtained from Equation 1. • Abs H: Absolute residual obtained from Equation 2. • Abs KH: Absolute residual obtained from Equation 3. • Abs CRH: Absolute residual obtained from Equation 4. • Abs CRHKH: Absolute residual obtained from Equation 5.

Table 11 The mean values and the 95% confidence intervals of the absolute deviations for the residuals of the five equations.

Equation	Mean value of the absolute deviation for the residuals	95% confidence interval (CI)
		Lower bound	Upper bound
Equation 1	5.53	4.45	6.61
Equation 2	5.86	4.80	6.91
Equation 3	5.53	4.51	6.54
Equation 4	3.38	2.71	4.05
Equation 5	3.14	2.60	3.69

Equation 1: PMI = 1.377K⁺ + 9.050.

Equation 2: PMI = 0.027Hx + 15.401.

Equation 3: PMI = 0.978K⁺ + 0.014Hx + 9.178.

Equation 4: PMI = 2.02 rigidity + 6.31 hypostasis + 6.94 corneal turbidity − 24.94.

Equation 5: PMI = 0.667K⁺ + 0.003Hx − 0.191 rigidity + 4.907 hypostasis + 4.68 corneal turbidity − 13.624.

Table 12 Pairwise comparisons of the differences between the mean values of the absolute deviations for the residuals of the five equations.

Equation number	Equation 1	Equation 2	Equation 3	Equation 4
Equation 1	–
Equation 2
Difference value	0.330
p	1.000
Equation 3
Difference value	0.000	0.330
p	1.000	1.000
Equation 4
Difference value	2.145	2.475	2.145
p	0.005^*	0.0001^*	0.003^*
Equation 5
Difference value	2.389	2.719	2.388	0.243
p	0.0001^*	0.0001^*	0.0001^*	1.000

Equation 1: PMI = 1.377K⁺ + 9.050.

Equation 2: PMI = 0.027Hx + 15.401.

Equation 3: PMI = 0.978K⁺ + 0.014 Hx + 9.178.

Equation 4: PMI = 2.02 rigidity + 6.31 hypostasis + 6.94 corneal turbidity − 24.94.

Equation 5: PMI = 0.667K⁺ + 0.003Hx − 0.191 rigidity + 4.907 hypostasis + 4.68 corneal turbidity − 13.624.

* Statistically significant at p ⩽ 0.05.