Forensic Serology and Blood Testing

The examination of blood and other biological fluids or materials for purposes relevant to criminal investigations.

It may help establish contact, identify potential contributors, reconstruct events, or exclude proposed associations.

A screening test indicating that a stain may contain blood without conclusively establishing its identity.

A presumptive blood test using phenolphthalein chemistry to detect blood-associated catalytic activity.

The presence of a substance producing the expected reaction, consistent with possible blood but requiring further interpretation.

Certain oxidizing agents, plant materials, or other substances may produce similar chemical reactions.

To help visualize possible blood traces through a chemiluminescent reaction, including some stains not readily visible.

No. Other substances may react, and additional testing is needed to establish the nature of the material.

An examination intended to provide more specific evidence that a questioned material contains blood, subject to the method's limitations.

Hemochromogen crystals that may be formed in a traditional confirmatory microscopic test for blood.

Hemin crystals that may be produced in a traditional microcrystal test for blood.

To evaluate whether a blood sample is of human origin rather than originating from another species.

A traditional immunological test used to assess the species origin of proteins in biological material.

No. Many people share the same ABO blood group.

The presence or absence of A and B antigens on red blood cells.

The presence or absence of the D antigen, commonly reported as Rh-positive or Rh-negative.

The examination of bloodstain size, shape, distribution, and other features to evaluate possible mechanisms of deposition.

A stain formed primarily through the action of gravity, such as a drip, flow, or pool.

A stain produced when a blood-bearing surface contacts another surface.

A stain formed when blood is propelled through the air by a force beyond gravity alone.

A bloodstain resulting from a drop of blood falling under the influence of gravity.

An accumulation of liquid blood on a surface.

A pattern formed as liquid blood moves across a surface under gravity or other forces.

A transfer pattern formed when a blood-bearing object moves across a surface.

A pattern produced when an object moves through an existing wet bloodstain and alters it.

An area lacking expected staining because an object or person may have interrupted deposition.

A smaller bloodstain formed when part of a larger drop separates during impact.

A pointed extension radiating from the edge of a bloodstain.

The two-dimensional region where estimated paths of multiple blood droplets intersect when projected onto a plane.

The estimated three-dimensional region from which blood droplets originated.

For an ideal elliptical stain, the impact angle may be estimated using the inverse sine of the width divided by the length.

Impact angle = arcsin(width ÷ length), using appropriate measurements of an interpretable elliptical stain.

Surface texture, stain distortion, overlapping stains, and nonideal droplet behavior can affect measurements.

No. Stain size is influenced by multiple factors and cannot independently identify a specific weapon.

The analysis of selected genetic markers to compare biological samples and assess possible contributors.

Short tandem repeat.

Their repeat patterns vary among individuals, allowing informative comparisons across multiple genetic locations.

Polymerase chain reaction, a laboratory technique used to amplify selected DNA regions.

A biological sample containing DNA from two or more contributors.

Contributors may share alleles, contribute unequal amounts of DNA, or produce low-level and stochastic effects.

A known sample used to assess whether biological material may have originated from someone such as a responder or laboratory staff member.

The indirect movement of DNA from one person or object to another through an intermediate contact or surface.

No. Direct contact, indirect transfer, persistence, and contamination must be considered.

To reduce the risk of introducing unrelated biological material or cross-contaminating samples.

Moisture can promote microbial growth and degradation of biological material.

It permits moisture exchange and may reduce conditions that encourage biological degradation.

A.M. No. 06-11-5-SC, the Supreme Court rule governing the use and evaluation of DNA evidence in applicable proceedings.

The reaction identifies a possible blood-related lead; further testing and contextual evaluation are required.

Assuming that every contributor participated in the crime or that the mixture establishes when and how DNA was deposited.

Surface effects, stain distortion, measurement reliability, and whether the stain is suitable for the calculation.

Loss of specimen identity and possible cross-contamination, which may undermine reliable interpretation.