Ch 3: Introduction to Urinalysis

ultrafiltrate of plasma

kidneys form urine as

1200 mL

average daily urine output

95% water, 5% solute (urea, organic, inorganic chemicals dissolved in water)

urine composition

urea

• half of total dissolved solids in urine

• metabolic waster product produced in the liver

• breakdown of protein & amino acids

urea, creatinine, & uric acid

organic substances in urine

chloride, sodium, potassium

major inorganic solid dissolved in urine

• urea, creatinine, sodium chloride are higher in urine

• protein & glucose not present in a normal urine specimen

best way to determine whether a fluid is urine is to consider the components

body’s state of hydration

amount excreted is determined by

• fluid intake

• fluid loss

• nonrenal sources

• variation in the secretion of antidiuretic hormone

• need to excrete amounts of dissolved solids: glucose or salts

factors that influence urine volume

1200-1500 mL

average normal daily urine output

600-2000 mL

normal range of daily urine output

oliguria

decrease urine output

• infants: < 1 mL/kg/hr

• children: < 0.5 mL/kg/hr

• adults: < 400 mL/day

oliguria

seen commonly when the body enters a state of dehydration from excessive water loss from vomiting, diarrhea, perspiration, or severe burns

anuria

oliguria leads to cessation of urine flow as a result from any serious damage to the kidneys or from decrease in the flow of blood to the kidneys

day

kidneys excrete 2-3 times more urine during

nocturia

increase in the nocturnal excretion of urine

polyuria

• children: > 2.5-3 mL/kg/day

• adult: > 2.5 L/day

increase in daily urine volume

diabetes mellitus & diabetes insipidus

polyuria is often associated with

suppress the secretion of ADH: diuretics, caffeine, alcohol

polyuria may be induced artificially

DM: defect in pancreatic production of insulin or in the function of insulin → increasing glucose → kidneys do not reabsorb glucose → compensation: increased excretion of water to remove glucose

DI: decrease in production or function of ADH

diabetes mellitus & diabetes insipidus produce polyuria for different reasons

specific gravity

DM: high (due to glucose content)

SI: low (truly diluted)

how to differentiate DM vs DI in analysis of urine

polydipsia

polyuria

polyphagia

classic triad of diabetes

50 mL

recommended capacity of container

refrigeration @ 2-8 deg C

most common method of preservation

precipitation of amorphous urate & phosphate crystals

refrigeration may also cause

enzyme reactions on the strips perform best at room temperature

specimens must be returned to room temperature before chemical testing

random specimen

• most common

• collected at any time

• routine screening tests

first morning specimen

• ideal screening specimen

• concentrated, ensuring detection of chemicals & formed elements