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Forensic Biology Evidence Information-Serology Analysis

 

Serology Analysis

In forensic casework, serology is the identification of body fluids, such as seminal fluid and blood.

There are two types of tests that are used in forensic serology analysis.

A presumptive test is a chemical test which, by production of color or light, indicates the presence of a body fluid.  It is typically more sensitive and less specific than a confirmatory test.

A confirmatory test is a test that verifies the presence of a specific compound.  It is typically less sensitive than a presumptive test but more specific.

The OSBI tests two categories of body fluids:  blood and seminal fluid.

 

Blood Analysis

Picture of Hemastix, Takayma, RSID-Blood

 

The presumptive test used for the detection of blood in the FBU is the Hemastix test from Miles Laboratories.  The test consists of a plastic strip with a reagent treated filter paper tab at one end.  The tab contains Tetramethylbenzidine (TMB), diisopropylbenzene dihydroperoxide, buffering materials, and non-reactants.  Testing the blood stain is conducted by rubbing the stain with the Hemastix strip and adding distilled water to the tab.  The reagent pad will turn green or blue-green to indicate a positive test.

The confirmatory test used to confirm the presence of blood in the FBU is the Takayama test.  This is a crystalline test that is viewed using a microscope.  A small cutting of the stain is placed on a microscope slide, and the reagent is allowed to flow between a cover slip and the sample to saturate the sample.  The test is positive if the analyst observes pink or red, rhomboid or needle shaped crystals (microcrystalline characteristics) that exhibit birefringence under plane polarized light.  This test will confirm only that blood is present and is not species specific. The test works regardless of the blood being human or animal.

The confirmatory test used to confirm human blood in the FBU is RSID-Blood, an immunological based test, provided by Independent Forensics.  RSID-Blood is an antigen-antibody test, using glycophorin A found in the red blood cells.  This test is similar in appearance to a home pregnancy test.  The sample is placed in the sample window of the cassette and allowed to wick through the cassette. A positive result will be indicated by the presence of two red lines forming on the cassette detection strip.  If the test is negative, only one line will form.

 

Seminal Fluid Analysis

AP Spot Test, p30, Cell Search Picture

 

The presumptive test used in the FBU for the detection of seminal fluid is the Acid Phosphate (AP) spot test.  Acid phosphatase (AP) is a class of enzymes that can catalyze the hydrolysis of certain organic phosphates.  The AP spot test is a color change test conducted by rubbing the suspected stain with a swab or filter paper and adding the AP spot test solution.  A positive test result will be indicated by a purple color change observed within two minutes.  This test is a presumptive test for the presence of acid phosphatase only. A positive result obtained indicates additional testing is necessary.

The p30 Prostate Specific Antigen (PSA) Immunoassay test is used in the FBU to detect p30.  p30 is a protein that is found in high concentrations in seminal fluid; however, it is also found in much lower concentrations in other body fluids such as breast milk, saliva, urine, etc.  The OSBI FBU uses the Seratec p30 card, which is a chromatographic immunoassay test that utilizes antigen-antibody reactions.  The test is similar to a home pregnancy test and is packaged as a cassette.  The sample is placed in the sample window and allowed to wick through the cassette.  A positive result for p30 will be indicated by the presence of three pink lines.  If the test is negative, only two lines will form.

The confirmatory test available for seminal fluid detection in the FBU is the microscopic identification of spermatozoa.  This test is accomplished by taking a small amount of the sample and placing it on a microscope slide.  The sample is stained with a two-part stain, commonly referred to as the X-mas tree stain, that aids the analyst in visually identifying the sperm.

 

Hair Analysis

The OSBI FBU does not perform hair comparisons; however the unit will look at hair to determine if it is a human or animal hair.  If the hair is determined to be of human origin, then a determination will be made of the hair to determine if it is suitable for nuclear DNA analysis.  The OSBI FBU does not perform mitochondrial DNA analysis; therefore, mitochondrial DNA analysis necessary for a case will be referred to the Federal Bureau of Investigation’s mitochondrial laboratory which may perform the mitochondrial DNA analysis. The OSBI FBU will assist with contacting the FBI regarding case acceptance.