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Positive and Presumptive Tests for Biological Fluids
Terms in this set (53)
What is a visualization-enhancing chemical that causes bloodstains to glow in the dark - even trace amounts?
What is water-based, may dilute bloodstains, HIGHLY sensitive but used as a last resort; can help visualize bloody impressions
What fixative protein-dye is useful for bloody impressions and stains residues a blue-black color?
what do most presumptive tests for blood rely on?
peroxidase activity of hemoglobin and oxidation of chemical indicators
Describe the method used to test a sample for blood using the Kastle-Meyer or Leucomalachite Green reagent
Add drop of reagent to a stain extract (dry rub on filter paper). Add a drop of hydrogen peroxide and color change is observed. 20 seconds or less = positive. Before hydr peroxide or longer than 20-30 seconds considered neg.
why might Leucomalachite Green be preferred in a presumptive test for blood over the Kastle-Meyer test?
The reagent phenolphthalein is time consuming to make
Describe the process of using hemastix to test a sample for blood
Add a drop of water to strip then rub against stain in question. They contain TMB which is a reagent used independently like kastle meyer.
Describe one advantage and disadvantage to using hemastix
Strips are a one step process and can be done quickly without reagents. Specificity is lower than other test and can be difficult to get stain to transfer.
what are the 2 microchemical confirmatory test for blood?
Takayama (hemochromogen) and Teichman reaction
Describe the process of the hemochromogen (Takayama) test
ferrous iron from Hgb reacts w/ pyridine to produce red feathery crystals. They are observed w/ light microscope.
T/F Microchemical confirmatory tests are not easily disrupted by debris and dirt, and are more sensitive than color tests
T/F one way of confirming blood is to visualize RBCs under a microscope, but the success of this method depends on the skill of the analyst and age of the stain as well as nature of the surface from which the stain came
T/f one reliable confirmatory test for blood is spectroscopy, and has been useful especially in aged and degraded stains that tested negative for color and microchemical tests
In relation to confirmation of blood, describe how spectroscopy works
identifies between Hgb and Hgb derivatives like methemaglobin, carboxyhemoglobin, sulfhemoglobin and oxyhemoglobin. all derivatives exhibit a strong absorbance at 400-425 nm (soret band)
what is the most commonly used confirmatory test for blood?
ABA Card hematrace
Describe how the ABA Card Hematrace works, and state one reason why investigators may not use it
Detects Hgb. Based on antibody-antigen rxn to antibodies in test card. Similar to preg test. Positive rxn w/ ferret blood - some labs will not use and some will process but give this disclaimer
Why is ALS useful in detecting semen stains?
it has fluorescing properties due to bacteria and flavins present. Visualized using 400-500nm wavelengths and using orange goggles in a dark room
T/F ALS visualization of suspected semen stain with a crusty touch is considered positive
False - ALS is merely a screening tool
What're the two most popular presumptive tests for semen?
AP spot and BCIP
T/F: a smal semen stain that dries quickly can have intact sperm for months possibly
Most presumptive semen tests look for the presence of what substance found in high quantities in semen?
describe how the AP spot test works
based on hydrolysis of phosphate esters; acid phosphatase reacts w/ sodium-alpha-napthylphosphate and fast blue B to produce purple/blue color. Positive result is intense color in 20-30 seconds. can be 1 step or 2 step process. Can use AP reagent on filter paper rubbed from stain.
Describe how the BCIP test works
swabbing of stain and adding to tube w/ BCIP. If AP is present it will hydrolyze the BCIP creating blue color changes w/in 15 mins.
what substances have been known to cause false positives of presumptive semen tests?
carrot/cauliflower juices, blood, male urine, fem hygiene prods, spermicides, vaggie fluids, blood
what protein in semen comes from the prostate and is especially important in semen samples of aspermic or oligospermic males?
How do the ABA Card P30 and Seratec PSA Semi-quaint work? Are they presumptive or confirmatory?
Antibody/antigen rxn between PSA & antibodies on test card. Sim to hematrace. Both work similarly; seratec has semi-quantitative internal control 4ng/mL
what is the most reliable technique for confirming the presence of sperm?
what type of stain is commonly used in the US for sperm?
Christmas Tree stain
what're the specific stains used in christmas tree stain?
. Nuclear fast red for Heads (DNA), counter stain of PIC for tails (blue-gray)
when is a microscopic analysis of sperm considered positive?
Sample is positive when any number of intact heads and tails are observed on slide. Presence of three or more heads and no visible tails can also be positive in some labs, depending.
T/F: SpermPaints fluorescent dye w/ antibodies bind to sperm head and tail antigens. Selective only for sperm and won't stain anything else.
True. use in conjuction w/ laser micro-dissection microscope.
T/F Saliva can be difficult to visualize on ALS because it may not fluoresce as well as other fluids
What's the most common test for saliva, because of its sensitivity and specificity?
T/F Vaginal fluids, breast milk may produce false positives for saliva / salivary amalyse
Saliva is alkaline or acidic?
Describe the radial diffusion test for saliva
Not sensitive, false +s. uses agarose gel w/ starch, extract of unknown sample is added to hole in gel, diffuses - amylase in sample hydrolyzes starch produces a clear area after staining w/ iodine. Size of area proportional to amount of amylase in sample.
Describe the way the phadebus test works
Amylase substrate is in an insoluble blue dye, linked to starch. Amylase in sample hydrolyses polymer; can be measured colorimetrically at 620 nm Absorbance in value that exceeds 0.3 units considered positive.
What test comes in prepackaged vials, clear solution that changes to yellow with addition of an extract that contains saliva?
What 'confirmatory' test for saliva is new, based on antibody-antigen reaction, but has known to have false positives with breast milk, fecal matter and vaginal fluids?
RSID - rapid-stain identification of saliva
T/F there are no confirmatory tests for urine. presence of urine is only inferred from the positive presumptive tests
T/F urine can be detected using ALS and will chemiluminesce a blue-white
Describe the method used in the Jaffe test
detects creatinine. Creatinine forms red compound with addition of piric acid
describe the way the urea litmus paper test works
indirectly indicates presence of urea by reacting to urease, generating ammonia from urea. Ammonia indicated using litmus paper (basic - pH).
which test for urine shows ammonia indicated by production of deep blue color in test tube
urea nitrogen tube test
describe characteristics of urine under a microscope
urine contains solid materials with characteristic crystalline structures + epithelial cells
what compound gives feces its characteristic odor?
what presumptive test for feces has been disputed but reacts with urobilinogen?
what is the oldest method of identifying fecal matter, and what characteristics identify it as feces?
Microscopy. Undigested residues of food within last 12-24 hours - characteristic fibrous materials found in animal meat, fruit, grain, veggs & fish
what bacteria in feces are strong presumptive evidence?
T/F there several confirmatory tests for vaginal secretions
False - tests are presumptive in nature
tests for identifying vaginal secretions screen for what?
what test for vaginal secretions is highly subjective; not widely used; when is a positive called?
Lugol's test; when majority of cells stain chocolate brow from yellow color
name 3 presumptive tests for blood
luminol, kastle-meyer (phenolphthalein), Leucomalachite Green, o-tolidine, benzidine, tetra-methyl benzidine, hemastix
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