Persistence of bloodstains on domestic surfaces treated with detergents: experimental evaluation using Combur Test®

The identification of latent blood traces on cleaned surfaces represents a crucial challenge in forensic practice, especially in cases of intentional removal attempts by the perpetrator. This study evaluated the effectiveness of Combur Test® strips, based on the peroxidase activity of hemoglobin, in detecting residual blood traces on nine types of domestic surfaces subjected to cleaning with five different detergents, applied either immediately or after 48 h from deposition. Ninety samples were analyzed, classifying reactivity on a semi-quantitative scale (0–3) and subjecting the data to statistical analysis. Surface type proved to be the main discriminating factor (ANOVA p < 0.001): cardboard, synthetic leather, and cotton retained higher mean reactivity values (2.70–2.80), whereas plastic, stainless steel, and PVC showed lower values (1.3–1.5). Cleaning timing significantly influenced results (t-test p = 0.013), with a reduction of mean reactivity in samples treated after 48 h (1.98) compared to those cleaned immediately (2.40), suggesting that progressive dispersion and more difficult rehydration of residues reduce test sensitivity as the time interval increases. In contrast, detergent type did not produce statistically significant differences (p = 0.251). Overall, strong reactions accounted for 43% of observations, while absence of reactivity was rare (1%). In conclusion, Combur Test® is confirmed as a rapid and cost-effective method for preliminary screening of latent blood traces. However, its sensitivity is influenced by both substrate nature and timing of the crime scene investigation, highlighting the need for prompt intervention and integration with confirmatory tests in cases of smooth surfaces, recent cleaning, or delayed sampling.