History of Forensic Serology and Immunological Methods

In 1901 Karl Landsteiner, working at the Vienna Pathological-Anatomical Institute, described four patterns of agglutination when human sera and red cells were mixed across individuals. He identified groups A, B, and O (initially called C); a fourth group, AB, was described shortly after by his colleagues Decastello and Sturli. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for this work. The forensic significance was not immediately obvious: the original motivation was clinical, to explain transfusion reactions. But within a decade, practitioners recognised that a dried bloodstain could be assigned to an ABO group and that this assignment, stable in aged material under the right conditions, could associate or exclude a suspect.

The first court use of ABO blood-group evidence in a criminal case is generally attributed to German courts in the early 1920s. By the 1930s, ABO typing of bloodstains was an established forensic procedure in Germany, Austria, the United Kingdom, and Japan. The method used was the absorption-elution technique, which detects ABO antigens on red cells even in dried stains by allowing specific antibodies to bind and then recovering them by heating, followed by agglutination testing. This technique extended the forensic reach of blood typing to stains weeks or months old.

A critical limitation was apparent from the start: ABO typing assigns a bloodstain to a group shared by a substantial fraction of the population. Group O is the most common type in most populations, found in approximately 44% of people of European descent, around 49% in India, and over 60% in some Indigenous American populations. A bloodstain typed as group O narrows the population but cannot identify an individual. This limitation drove the search for additional polymorphic markers throughout the twentieth century.

Also in 1901, Paul Uhlenhuth at the University of Greifswald described the precipitin test for human blood. Uhlenhuth immunised rabbits with human serum, then demonstrated that the resulting antibodies produced a precipitate specifically when mixed with human serum but not with serum from other species. In a now-celebrated case that year, he applied the test to material from a murder case in Rugen, Germany, confirming the presence of human blood and excluding animal blood on a suspect's tool. The test had immediate practical utility: it answered the question courts asked, namely whether a stain was human blood at all, before any further characterisation.

The standard forensic precipitin test, sometimes called the Ouchterlony double-diffusion test in its gel-diffusion form, works on the same principle. Known antisera specific to different species are placed in wells in agar alongside unknown sample wells. Each diffuses toward the other; where the concentrations meet and the proteins match, a visible precipitation band forms. Multiple antisera can be run in parallel, allowing species identification from a single test. Antihuman antisera remained standard in forensic laboratories throughout the twentieth century as the first confirmatory test applied to any suspected bloodstain.

The precipitin test has well-documented limitations on heavily degraded material. Proteins denature with heat, ultraviolet exposure, and microbial action. A stain several years old in unfavourable conditions may give a weak or absent precipitin reaction even when its origin is human. Later immunological methods, particularly ELISA, were applied to species identification precisely because of their superior sensitivity on degraded material.

The Rh blood group system, discovered in 1940 by Landsteiner and Wiener, added a second major antigen system to the forensic toolkit. Rh typing combined with ABO reduced the population fraction consistent with any given two-system result. Through the mid-twentieth century, forensic serologists systematically evaluated additional systems: MNS (described in 1927), Kell (1946), Duffy (1950), Kidd (1951), and others. Each new typing system, if reliably performable on dried stains, multiplied the discriminating power of the combined panel.

Secretor status added a further dimension. Approximately 80% of people secrete their ABO antigens into body fluids including saliva, semen, sweat, and vaginal secretions. A secretor's saliva swab or semen stain can be ABO typed using the same absorption-inhibition technique applied to bloodstains. The remaining 20%, non-secretors, produce no detectable ABO antigen in these fluids. Identifying secretor status from a semen or saliva stain was a routine forensic procedure from the 1960s onward, particularly important in sexual assault cases where semen evidence was present but no blood was recovered. The secretor gene (FUT2) is now characterised at the molecular level, but its population-level serology was established decades earlier.

Red-cell enzyme polymorphisms, including phosphoglucomutase (PGM), esterase D, and adenylate kinase, were added to forensic panels from the 1960s. These were typed by isoelectric focusing, a gel electrophoresis technique that separates enzyme variants by charge. PGM typing in particular became a standard forensic procedure in the UK and US; the 1984 case against Colin Pitchfork (later resolved by DNA) initially relied on ABO and PGM typing to narrow the suspect pool. By the mid-1980s, a combined ABO, Rh, MNS, PGM, and EsD panel could generate random-match probabilities in the range of one in several hundred to one in several thousand, far short of modern DNA profiling but a substantial advance over ABO alone.

Rosalyn Yalow and Solomon Berson developed radioimmunoassay (RIA) in 1959 to measure circulating insulin in diabetic patients. The principle, competitive binding between a radiolabelled antigen and unlabelled antigen for a fixed number of antibody sites, offered sensitivity far beyond anything achievable with precipitation or agglutination. Yalow received the Nobel Prize in Physiology or Medicine in 1977. Forensic and toxicological laboratories adopted RIA during the 1970s primarily for drug detection: the technique could detect nanogram quantities of drugs such as opioids, barbiturates, and amphetamines in urine or blood. The limitation was the requirement for radioactive isotopes, the associated regulatory controls, and the disposal requirements, all of which made RIA unsuitable for most routine forensic casework.

Eva Engvall and Peter Perlmann in Stockholm, and simultaneously Bauke van Weemen and Anton Schuurs in the Netherlands, published the enzyme-linked immunosorbent assay in 1971. ELISA replaced the radioactive label with an enzyme that generates a measurable colour change on substrate addition, retaining the sensitivity advantage of RIA while eliminating the radioisotope requirement. The technique was rapidly adopted in clinical diagnostics and research, and from the late 1970s onward began to appear in forensic applications.

In forensic serology, ELISA offered three advantages over earlier methods. First, sensitivity: ELISA could detect body-fluid proteins in nanogram quantities, making it useful for highly diluted or degraded samples. Second, specificity: the assay could be designed around antibodies specific to proteins unique to particular body fluids, such as prostate-specific antigen (PSA) for semen or amylase for saliva. Third, format flexibility: sandwich ELISA, competitive ELISA, and indirect ELISA formats allowed adaptation to different analytes and sample types without redesigning the entire assay platform. Forensic laboratories in the UK, US, Germany, Australia, and elsewhere had incorporated ELISA-based confirmatory assays for semen identification by the early 1990s.

Georges Kohler and Cesar Milstein described the hybridoma method for producing monoclonal antibodies in 1975, for which they received the Nobel Prize in Physiology or Medicine in 1984. A monoclonal antibody is produced by a single clone of fused antibody-producing and tumour cells, yielding an unlimited supply of antibody with defined, reproducible specificity against a single epitope. For immunoassay development, this was a decisive change: assay-to-assay variability from polyclonal antisera was a persistent source of forensic quality-control concern, and monoclonal reagents removed it.

Lateral-flow immunoassay technology, commercialised in the 1980s initially for home pregnancy testing (detecting human chorionic gonadotropin), was adapted for forensic body-fluid identification from the late 1990s. The format uses nitrocellulose membrane strips on which monoclonal antibodies are immobilised in test and control zones. A liquid sample carrying the target antigen migrates by capillary action; labelled antibody in the conjugate pad binds the antigen; the complex is captured at the test line, generating a visible coloured line. The entire process takes two to five minutes and requires no reagents beyond the sample. Devices validated for forensic use include ABAcard HemaTrace for human haemoglobin, ABAcard p30 for semen, and lateral-flow tests for saliva and menstrual blood.

These devices are classified as presumptive or confirmatory depending on the validation level. HemaTrace is used as a highly sensitive confirmatory test for human blood in many jurisdictions, having demonstrated specificity for human and a small number of closely related primate haemoglobins. ABAcard p30 performs as a confirmatory test for semen in many laboratory protocols, replacing earlier acid-phosphatase spot tests. The speed and simplicity of lateral-flow devices have extended serological triage to the crime scene and to high-volume processing settings, both of which were previously impractical with bench ELISA.

Alec Jeffreys developed DNA fingerprinting at the University of Leicester in 1984. The first forensic DNA case, the Enderby murders in Leicestershire, was resolved in 1986. Polymerase chain reaction (PCR), described by Kary Mullis in 1983, made DNA profiling practical on the minute and degraded samples typical of forensic evidence by the early 1990s. Short tandem repeat (STR) profiling, which delivers random-match probabilities of one in billions, displaced blood-group serology for individual identification across most forensic laboratories by around 2000.

The displacement was not elimination. Forensic serology retained a defined and necessary role as the analytical layer that precedes DNA profiling. Before committing to extraction and amplification, a laboratory needs to know what a stain is: blood, semen, saliva, or another body fluid. That determination is immunological. It also needs to know the stain is human, not from an animal that contaminated the scene. That determination, historically the precipitin test and now a lateral-flow or ELISA assay, is also immunological. The sequence in a modern laboratory is: presumptive test (colour reaction or immunochromatographic strip), confirmatory test (ELISA or validated lateral-flow), then DNA extraction.

Relationship testing is a domain where immunological methods were comprehensively replaced. Pre-DNA paternity testing used ABO, Rh, MNS, and enzyme panels; post-DNA, STR profiling at 15 to 20 loci produces statistical power no blood-group panel can approach. In India, the courts recognised blood-group typing for paternity purposes under the Indian Evidence Act until the 1990s; courts today rely on DNA, governed by guidelines from bodies such as the Central Forensic Science Laboratory (CFSL). Similarly in the UK, the Child Support Agency and courts moved entirely to DNA-based paternity testing by the late 1990s, and US state courts followed the same trajectory.

Immunological methods continue to develop in directions specific to forensic needs. Multiplex lateral-flow panels that detect several body-fluid markers simultaneously from a single sample have entered validation pipelines. Microfluidic immunoassay platforms that integrate the full sequence from sample preparation to result on a single chip are under active development. The underlying principle throughout the discipline's history remains the same as in 1901: an antibody with defined specificity for a target molecule is the instrument, and the forensic problem is always one of detection, identification, and interpretation of that target.