Direct Comparison of Body Fluid Identification Technologies

Crime scenes, particularly those involving violence, often yield evidence from bodily fluids - blood, saliva, urine, semen - left behind. However, discerning the composition and source of the fluids is more complicated than one might think, particularly when several sources are mixed together. If forensic scientists can identify a fluid's source, they might gain critical information about a person's involvement with a crime and what happened. In the tragic case of five-year-old Harmony Montgomery, whose body has still not been recovered, investigators were able to reconstruct events by analyzing fluid-soaked ceiling tiles retrieved from a shelter the Montgomery family had visited. They found blood evidence that led prosecutors to allege Montgomery's father had temporarily stored her body in the shelter's ceiling before he later moved it.[1]

In recent years, forensic investigators expressed the need for body fluid identification technologies that identify fluids more accurately and with greater sensitivity than traditional immunoassay methods.[2] Fortunately, several new methods have been introduced that meet this demand. Collectively referred to as "omic"-based methods, they are now available for fluid identification purposes (Table 1). National Institute of Justice (NIJ)-funded researchers recently released the results of a study designed to compare the specificity and sensitivity of these "omic"-based methods.

Table 1. Emerging "omic"-based approaches to body fluid identification, including epigenomics, transcriptomics, and proteomics.

Dr. Mirna Ghemwari, from the Center for Forensic Science Research and Education, combined expertise with Dr. Jack Ballantyne (transcriptomics), Dr. Bruce McCord (epigenomics), Dr. Glendon Parker (shotgun proteomics), and the New York Office of the Chief Medical Examiner (targeted proteomics). They investigated the specificity and sensitivity of epigenomic, transcriptomic, and proteomic methods for body fluid identification, as well as their accompanying error rates, so crime labs could make informed decisions about which approach to use.

Procedure Standardization and Sample Testing: A Two-Phase Approach

In the first phase, researchers standardized sample preparation methods to ensure fluid technology calibration. Ghemrawi sent samples from five fluid types (semen, venous blood, saliva, vaginal fluid, and menstrual blood) to external labs for identification. The source of the body fluids was withheld from the testing labs until all results were gathered and compared. Analyses indicated that the best results were generated when samples were not diluted with water and swab slurries were not used.

In the second phase, researchers analyzed mock casework samples. They deposited 58 samples consisting of nine fluid types[3] on different types of substrates at a variety of volumes. Then, they identified the fluid type using six methods: two types of traditional immunoassay (methods A and B), DNA methylation, mRNA testing, shotgun proteomics, and targeted proteomics (Figure 1).

Figure 1. Comparison of specificity, sensitivity, and error rates of the body fluid identification assays: targeted proteomics, mRNA, DNA methylation, the traditional immunoassay methods A and B[ii], and shotgun proteomics.