chapter 6: identification of blood
TRANSCRIPT
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Chapter 6: Identification of Blood
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Normal blood volume is 8% of body weight▪ = 5-8 pints for average adults▪ Fatal if lose 40% or more of blood volume
Two portions: Fluid portion▪ Plasma- fluid portion of blood that can clot▪ Serum- remaining fluid after clot is removed
Cellular Portion▪ Red blood cells (erythrocytes; hemoglobin; No DNA)▪ White blood cells (Leucocytes; fight infection; DNA
present)▪ Platelets (Thrombocytes; blood clotting; No DNA)
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Plasma and serum
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Hemoglobin: Transports oxygen from lungs to body tissues; helps with transport of CO2 out of the tissues and back to the
lungs
Heme: Prosthetic group in
hemoglobin; Binds oxygen; also has peroxidase activity
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Presumptive Very sensitive, fast, and easy to perform Depend on oxidation-reduction reaction
catalyzed by heme group of blood Result in color change or release of photon by
chemiluminescence or fluorescence Confirmatory
Need a lab to perform; greater specificity Depend on crystal formation, primary
serological reactions, spectrophotometry, or RNA-based assays
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Detect traces of blood Oxidation-reduction reaction catalyzed by
heme Oxidation- lose electron▪ Hydrogen peroxide used as an oxidant▪ E.g. K-M test described in Lecture 5
Reduction- gain electronTests result in:
Change of color (colorimetric assays) Release of photons▪ Chemiluminescence or fluorescence
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Colorimetric Assays Phenolphthalein (Kastle-Meyer)▪ -Introduced in Lecture 5▪ We will perform this test in lab
Leucomalachite green (LMG)▪ Colorless in reduced state; green when oxidized
Benzadine and Derivatives▪ Benzadine colorless in reduced state; dark blue
when oxidized▪ Tetramethylbenzidine (TMB) colorless in
reduced state; blue-green when oxidized7
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Chemiluminescent assays Light is emitted as a product of the
chemical reaction Luminol- emits light blue color▪ Useful when blood has been cleaned up▪ Performed in darkness▪ Can detect small traces of blood▪ Can detect patterns▪ May dilute sample
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False positive results with luminol:▪ Bleach▪ Plants▪ Copper and copper-
containing alloys▪ Feces▪ Urine (if blood is
present, including menstrual blood)
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Fluorescence assays Absorption of UV or visible radiation kicks
electrons up to a higher orbitial (higher energy state)
When electrons drop down to original ground state:▪ Energy released is transferred to vibrational
and rotational energy of molecular bonds (most common)
▪ Energy released as a photon of lower energy wavelength (less common) = fluorescence
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Fluorescin▪ When oxidized by the
peroxidase activity of heme in the presence of hydrogen peroxide, will fluoresce
▪ Must be exposed to wavelength 425-485 nm (blue-purple) from an ALS
▪ Emits yellowish-green color (longer wavelength)
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Absorbs light here
Emits (fluoresces)
light here
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Microcrystal assays Hemochromagen crystal assay (Takayama) Hematin crystal assay (Teichmann) Method:▪ Small amount of putative blood added to a slide▪ Chemical solution added▪ Slide heated to form crystals (if blood present)▪ Crystals viewed under the microscope
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Positive Takayama confirmatory test for blood
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Other Chromatographic and electrophoretic methods▪ Identify human hemoglobin based on mobility on
columns or in gels Spectrophotometric methods▪ Identify human hemoglobin based on light spectra
absorbed by hemoglobin and its derivatives Immunological methods▪ Anti-human hemoglobin antibodies (see Lecture 5)
RNA-based methods▪ Assay for presence of mRNAs found only in human
blood15