Intro to Urinalysis

how much plasma is filtered by the kidneys per day?

170,000 mL

what is the normal amount of urine output per day?

1200-1500 mL (600-2000 mL acceptable)

what is urea?

a metabolic waste product formed from the breakdown of protein and amino acids

what organic chemicals can be found in urine?

urea, creatinine, and uric acid

what inorganic chemicals can be found in urine?

chloride, sodium, and potassium

what formed elements can be found in urine?

cells, casts, crystals, mucus, and bacteria

which substances are not normally found in urine?

protein and glucose

what is oliguria?

decrease in urine output, less than 400 mL/day in adults

what is anuria?

no urine output

what is nocturia?

increased urine output at night

what is polyuria?

increased urine output, greater than 2.5 L/day

what is diabetes mellitus?

increased concentration of blood glucose due to inadequate production or function of insulin

what is diabetes insipidus and why does it cause polyuria?

inadequate production or function of ADH

why does diabetes mellitus cause polyuria?

excess unabsorbed glucose means the kidneys have to excrete more water to “flush it out” from the body

why does diabetes insipidus cause polyuria?

inadequate production or function of ADH causes the collecting duct to remain impermeable to water, causing higher urine output

does diabetes mellitus cause urine to have a high or low specific gravity?

high, due to excess glucose

does diabetes insipidus cause urine to have a high or low specific gravity?

low, as less water is reabsorbed and urine remains dilute

what is the recommended capacity for a urine collection container?

50 mL

how much urine is needed for microscopic analysis?

12 mL

what is the maximum amount of time a urine specimen can remain unrefrigerated or unpreserved before reaching the lab?

2 hours

how and why does the color of urine change when it is not refrigerated or chemically preserved?

the color can be modified/darkened due to oxidation or reduction of metabolites

how and why does the clarity change in urine that is not refrigerated or chemically preserved?

clarity decreases due to bacterial growth and precipitation of amorphous material

how and why does odor change in urine that is not refrigerated or chemically preserved?

urine will have an increased ammonia smell due to bacterial multiplication, causing the breakdown of urea to ammonia

how and why does pH change in urine that is not refrigerated or chemically preserved?

pH increases due to breakdown of urea to ammonia by urease-producing bacteria/loss of CO₂

how and why do glucose levels change in urine that is not refrigerated or chemically preserved?

glucose levels will decrease due to glycolysis and bacterial use

how and why do ketone levels change in urine that is not refrigerated or chemically preserved?

ketone levels will decrease due to volatilization and bacterial metabolism

how and why do bilirubin levels change in urine that is not refrigerated or chemically preserved?

bilirubin levels will decrease due to exposure to light/photo oxidation to biliverdin

how and why do urobilinogen levels change in urine that is not refrigerated or chemically preserved?

urobilinogen levels will decrease due to oxidation to urobilin

how and why do nitrite levels change in urine that is not refrigerated or chemically preserved?

nitrite levels will increase due to multiplication of nitrate-reducing bacteria

how and why do red and white blood cells and casts change in urine that is not refrigerated or chemically preserved?

red and white blood cells and casts will decrease due to disintegration/lyse in dilute alkaline urine

how and why do bacteria levels change in urine that is not refrigerated or chemically preserved?

bacteria will increase due to multiplication

how and why does trichomonas change in urine that is not refrigerated or chemically preserved?

trichomonas will decrease due to loss of motility and death

what temperature should urine be refrigerated at?

2^oC - 8^oC

how long can urine be refrigerated before use for a bacteria culture?

up to 24 hours

what are the advantages and disadvantages of refrigerating urine?

does not interfere with chemical tests, but precipitates amorphous phosphates and urates

what are the advantages and disadvantages of acid urine preservation?

prevents bacterial growth and metabolism, but interferes with analysis of drugs and hormones

what are the advantages and disadvantages of formalin (formaldehyde) urine preservation?

excellent sediment preservative, but acts as a reducing agent and interferes with tests for glucose, blood, leukocyte esterase, and copper reduction

what are the advantages and disadvantages of sodium fluoride as a urine preservative?

good preservative for drug analyses, but inhibits reagent strip tests for glucose, blood, and leukocytes

what are the advantages and disadvantages of commercial urine preservative tablets?

convenient when refrigeration is not possible and have controlled concentration to limit interference, but can still interfere with certain tests

what are the advantages of urine collection kits?

contain the collection cup, transfer straw, culture & sensitivity (C&S) preservative tube, or UA tube

what are the advantages and disadvantages of light gray and gray C&S tubes as urine preservatives?

keep specimen stable at room temperature for 48 hours and prevent bacterial growth and metabolism, but cannot be used if urine is below the fill line

what are the advantages and disadvantages of yellow UA plus tube as a urine preservative?

can be used on automated instruments but must be refrigerated within 2 hours

what are the advantages and disadvantages of cherry red/yellow preservative plus tubes?

keep the specimen stable for 72 hours at room temperature and are instrument-compatible, but urine must be filled to fill line and bilirubin and urobilinogen may be decreased if exposed to light and left at room temperature

what is the purpose of random urine specimens?

routine screening

what is the purpose of first morning urine collection?

routine screening, pregnancy testing, and orthostatic protein testing

what is the purpose of 24-hour urine collection?

quantitative chemical tests

what is the purpose of catheterized urine collection?

bacterial culture

what is the purpose of midstream clean-catch urine collection?

routine screening or bacterial cultures

what is the purpose of suprapubic aspiration urine collection?

bacterial cultures or cytology testing

what is the purpose of three-glass or four-glass urine collection?

prostatic infection diagnosis

which urine test is chain of custody especially important for?

drug screening

which urine is discarded during a 24-hour test?

the first void of the first day (because it’s produced by the body overnight and will cause falsely elevated results)