urine preservatives

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refrigeration

advantages: doesnt interfere with chemical tests
disadvantages: raises specific gravity by hydrometer, precipitates amorphous phosphates and urates
other info: prevents bacterial growth

thymol

advantages: preserves glucose and sediments well; good for formed elements
disadvantages: interferes with acid precipitation tets for protein, inhibits bacteria and yeast

boric acid

advantages:preserves protein and formed elements well; doesn't interfere with routine analyses other than pH
disadvantages: may precipitate crystals when used in large amounts
other info: keeps pH at about 6

formalin (formaldehyde)

advantages: excellent sediment preservative; good for formed elements
disadvantages: reducing agent, interfering with chemical tests for glucose, blood, leukocyte esterase, copper reduction
other info: rinse specimen container with formalin to preserve cells and casts

toluene

advantages: doesn't interfere with routine tests
disadvantages: floats on surface of specimens and clings to pipettes and testing materials

sodium fluoride

advantages: prevents glycolysis, good preservative for drug analyses (tests for glucose)
disadvantages: inhibits reagent strip tests for glucose, blood, and leukocytes
other info: may use sodium benzoate instead of fluoride for reagent strip testing

phenol

advantages: doesn't interfere with routine tests
disadvantages: causes an odor change
other info: use 1 drop per ounce of specimen

commercial preservative tablets

advantages: convenient when refrigeration is not possible, have controlled concentration to minimize interference
disadvantages: may contain 1+ preservatives include sodium fluoride
other info: check tablet composition to determine possible effects on desired tests

urine collection kits

advantages: contains collection cup, C&S preservative tube or UA tube

gray C&S tube

advantages: sample stable at room tep for 48 hrs; preserves bacteria
disadvantages: decreases pH; do not use if urine is below minimum full line
other info: preservative is boric acid and may not be used for UA

yellow pain UA tube

advantages: use on automated instruments
disadvantages: must refrigerate within 2 hours
other info: round or conical bottom

cherry red/yellow top tube

advantages: stable for 72 hours at RT; instrument-capable
disadvantages: bilirubin and urobilinogen may be decreased if specimen is exposed to light and left at RT
other info: preservative is sodium propionate; conical bottom

saccomanno fixative

advantages: preserves cellular elements
other info: used only for cytology studies

freezing

uses: bilirubin, urobilinogen
problems: destroys formed elements

HCl

uses: calcium, phosphorus, delta-aminolevulinic acid
problems: routine UA, destroys formed elements, bactericidal

sodium carbonate

uses: porphyrins, prophobilinogen, urobilinogen
problems: routine UA

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