Post mortem tryptase cut-off level for anaphylactic death.

Serum mast cell tryptase is used to support the diagnosis of anaphylaxis. The recommended clinical cut-off for total tryptase (<11.4µg/L) appears unsuitable in the post mortem setting due to largely unknown processes which result in significantly elevated levels in these samples. Consequently there is no widely accepted tryptase cut-off level for diagnosing an anaphylactic death. This 5-year retrospective study compared total tryptase levels in post mortem femoral blood in anaphylactic deaths and control. Univariate and multivariate analysis was used to assess the relative contribution of other factors (age, gender, post mortem interval, and presence of resuscitation) on post mortem tryptase levels. Nine anaphylactic deaths and 45 controls were identified. Receiver-operating characteristic (ROC) curve analysis identified an optimal cut-off of 53.8µg/L, with sensitivity of 89%, and specificity of 93%, for total post mortem tryptase in femoral blood to diagnosis anaphylaxis. No other factors showed any statistical significant contribution to post mortem tryptase elevation. Femoral total post mortem tryptase level of 53.8µg/L and above is a useful ancillary test in diagnosing an anaphylactic death.

Post mortem vitreous magnesium in adult population.

BACKGROUND: The study of post mortem vitreous magnesium (Mg) is less common than sodium (Na), chloride (Cl) and potassium (K) in the forensic literature. There is no accepted normal range for post mortem vitreous Mg and the relationship between post mortem vitreous Mg levels and post mortem interval (PMI), other electrolyte levels, disease conditions, age and sex have not been fully established. AIM: To investigate the relationship of post mortem vitreous Mg with age, sex, PMI, vitreous electrolyte levels and diabetic status. METHODS: A retrospective study of 20 consecutive cases of diabetics and 20 non-diabetic adult deaths was performed. Spearman correlation and the permutation test were used to explore the relationship between post mortem vitreous Mg and continuous and categorical variables respectively. RESULTS: The mean post mortem vitreous Mg was 1.03mmol/L (95%CI: 0.98-1.08mmol/L). The absolute Spearman correlation coefficients (rho) between post mortem vitreous Mg with PMI, age, and other vitreous electrolytes (Na, Cl, and K) ranged between 0.04-0.21 (p>0.19). Post mortem vitreous Mg was statistically higher in diabetics (mean difference: 0.08mmol/L; area-under-the-curve=0.65 on receiver-operator-characteristic curve). No statistical difference was demonstrated between sexes (p=0.92). CONCLUSIONS: In our adult population, post mortem vitreous Mg did not correlate with age, PMI, other vitreous electrolytes (sodium, chloride and potassium) or sex. It was higher in diabetics, however had limited utility as a surrogate marker. Overall, post mortem Mg is steady in the early post mortem period with a mean of 1.03mmol/L.

Differences in sampling techniques on total post-mortem tryptase.

BACKGROUND: The measurement of mast cell tryptase is commonly used to support the diagnosis of anaphylaxis. In the post-mortem setting, the literature recommends sampling from peripheral blood sources (femoral blood) but does not specify the exact sampling technique. Sampling techniques vary between pathologists, and it is unclear whether different sampling techniques have any impact on post-mortem tryptase levels. AIM: The aim of this study is to compare the difference in femoral total post-mortem tryptase levels between two sampling techniques. METHODS: A 6-month retrospective study comparing femoral total post-mortem tryptase levels between (1) aspirating femoral vessels with a needle and syringe prior to evisceration and (2) femoral vein cut down during evisceration. RESULTS: Twenty cases were identified, with three cases excluded from analysis. There was a statistically significant difference (paired t test, p < 0.05) between mean post-mortem tryptase by aspiration (10.87 ug/L) and by cut down (14.15 ug/L). The mean difference between the two methods was 3.28 ug/L (median, 1.4 ug/L; min, - 6.1 ug/L; max, 16.5 ug/L; 95% CI, 0.001-6.564 ug/L). CONCLUSIONS: Femoral total post-mortem tryptase is significantly different, albeit by a small amount, between the two sampling methods. The clinical significance of this finding and what factors may contribute to it are unclear. When requesting post-mortem tryptase, the pathologist should consider documenting the exact blood collection site and method used for collection. In addition, blood samples acquired by different techniques should not be mixed together and should be analyzed separately if possible.