A biochemical approach for assessing cutoffs at the age thresholds of 14 and 18 years: a pilot study on the applicability of bone specific alkaline phosphatase on an Italian sample

The majority of age estimation methods analyze morphological changes of specific skeletal (or dental) structures reflecting global bone development (biological parameter) in order to estimate a chronological value. This morphological and structural development is the consequence of a very active tissue metabolism and intensive modeling process which involve both bone formation and bone resorption. Several biochemical markers of bone formation and bone resorption are available, and specific biochemical tests can be performed on blood or urine samples, but such markers of bone turnover have never been employed for age estimation in living individuals for forensic purposes. The aim of this study was to ascertain the applicability of serum bone alkaline phosphatase (BALP) concentration in the age estimation for forensic purposes. We focused on the legal age thresholds of 14 and 18 years (LAT) because, in Italy, the former is considered the minimum age for criminal responsibility and the latter defines adult age and the possibility of applying general criminal laws.

This study analyzed, from a forensic point of view, BALP and Tanner stages of 202 healthy white individuals (116 females and 86 males) between the ages of 10 and 30 years.

We derived a linear logistic model to estimate the probability that an individual was older or younger than LAT using two variables: BALP concentration and Tanner stages. The predictive accuracy of the test was assessed by the determination of the receiver-operating characteristic curve (ROC curve). The test was performed to identify a threshold (cutoff) that could be used to assign an individual to the population of those younger or older than LAT.

ROC curve showed that the use of both serum BALP concentration and Tanner stages has a very good level of reliability in age assessment (the area under the ROC curve, AUC, ranged from 0.918 to 0.962). Best results were obtained in the assessment of male over 18 years of age (sensibility and specificity respectively of 0.90 and 0.93 with an accuracy of 0.92). Worst results were obtained in the assessment of female over 18 years of age (sensibility and specificity respectively of 0.87 and 0.82 with an accuracy of 0.84). We also calculated the probability of the correctness in the age estimation.

The results showed that the use of serum BALP concentration in the age assessment could be a promising and integrative method to established ones, but more research has to be done to validate the value of the proposed method in the forensic practice.