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viewed while held up to a light source.This operates on the principle that the refractive index of a urine specimen will vary directly with the total amount of dissolved solids in the sample.This instrument mea?sures the refractive index of the urine as compared with water on a scale that is calibrated directly into the ocularUrinary tract infections and bacterial contamination also will alkalinize pH. Medications such as potassium citrate and sodium bicarbonate will reduce urine pH. Alkaline urine is also found in Fanconi syndrome, a congenital gener?alized aminoaciduria resulting from defective proximal tubular function.This generally occurs after an initial period of anuria because the damaged tubules are unable to concentrate or dilute the glomerular filtrate.16 pH Determinations of urinary pH must be performed on fresh specimens because of the significant tendency of urine to alkalinize on standing.In alkaline urine, suspended precipitates of amorphous phosphates and carbonates may be responsible for turbidity, whereas in acidic urine, amorphous urates may be the cause.16 Volume The volume of urine excreted indicates the balance between fluid ingestion and water lost from the lungs, sweat, and intestine.Polyuria is observed in diabetes mellitus and insipidus (in insipidus, as a result of lack of ADH), as well as in chronic renal disease, acromegaly (overproduction of the growth hor?mone somatostatin), and myxedema (hypothyroid edema).Alkaline urine (pH > 7.0) is observed postprandially as a normal reaction to the acidity of gastric HCl dumped into the duodenum and then into the circulation or fol?lowing ingestion of alkaline food or medications.Acidity in urine (pH < 7.0) is primarily caused by phosphates, which are excreted as salts conjugated to Na+, K+, Ca2+, and NH4

• .Pathologic states, in which increased acidity is observed, include systemic acidosis, as seen in diabetes mellitus, and renal tubular acidosis (RTA).Brownish-black after standing is seen in alkaptonuria (a result of excreted homogentisic acid) and in malignant melanoma (in which the precursor mela?nogen oxidizes in the air to melanin).Urinary tract infections impart a noxious, fecal smell to urine, whereas the urine of diabetics often smells fruity as a result of ketones.Low SG can occur in dia?betes insipidus, pyelonephritis, and glomerulonephritis, in which the renal concentrating ability has become dysfunctional.Fixed SG (isosthenuria) around 1.010 is observed in severe renal damage, in which the kidney excretes urine that is iso-osmotic with the plasma.Owing to the Na+/H+ exchange pump mechanism of the renal tubules, pH (H+ concentration) increases as sodium is retained.The characteristic pungent odor of fresh urine is due to vola?tile aromatic acids, in contrast to the typical ammonia odor of urine that has been allowed to stand.SG varies with the solute load to be excreted (consisting primarily of NaCl and urea), as well as with the urine volume.High SG can be seen in diabetes mellitus, congestive heart failure, dehydration, adrenal insuffi?ciency, liver disease, and nephrosis.Acidity also reflects the excretion of the nonvolatile metabolic acids pyruvate, lactate, and citrate.In RTA, the tubules are unable to excrete excess H+ even though the body is in metabolic acidosis, and urinary pH remains around 6.Chemical Analyses Routine urine chemical analysis is rapid and easily per?formed with commercially available reagent strips or dipsticks.Anuria or oliguria (<200 mL/d) is found in nephritis, uri?nary tract obstruction, AKI, and kidney failure.Most recently, an indirect colorimetric reagent strip method for assaying SG has been added to most dipstick screens.Certain inborn errors of metabolism, such as maple sugar urine disease, are associated with characteristic urine odors.Turbidity The cloudiness of an urine specimen depends on pH and dissolved solids composition.The most commonly encountered analytic method consists of a refractometer, or total solids meter.Unlike the refrac?tometer, dipsticks measure only ionic solutes and do not take into account glucose or protein.Automated and semiautomated instruments that detect to green color is a result of bile pigment oxidation.SG gives an indication of the density of a fluid that depends on the concentration of dissolved total solids.It is used to assess the state of hydration/dehydration of an individual or as an indicator of the concentrating ability of the kidneys.These strips are plastic coated with different reagent bands directed toward different analytes.Colors on the dipstick bands are matched against a color chart provided with the reagents.Red and brown after standing are due to porphyrins, whereas reddish-brown in fresh specimens comes from hemoglo?bin or red cells.Turbidity generally may be due to gross bacteriuria, whereas a smoky appearance is seen in hematuria.When dipped into urine, a color change signals a d eviation from normality.Specific Gravity The specific gravity (SG) of urine is the weight of 1 mL of urine in grams divided by the weight of 1 mL of water.Correct cali?bration is vital for accuracy.SG will increase about 0.004 units for every 1% change in glucose concentration and about 0.003 units for every 1% change in protein.Drugs and some foods, such as beets, may also alter urine color.

viewed while held up to a light source. Correct cali￾bration is vital for accuracy. Most recently, an indirect
colorimetric reagent strip method for assaying SG has
been added to most dipstick screens. Unlike the refrac￾tometer, dipsticks measure only ionic solutes and do not
take into account glucose or protein.
The normal range for urinary SG is 1.003 to 1.035 g/mL.
SG can vary in pathologic states. Low SG can occur in dia￾betes insipidus, pyelonephritis, and glomerulonephritis,
in which the renal concentrating ability has become
dysfunctional. High SG can be seen in diabetes mellitus,
congestive heart failure, dehydration, adrenal insuffi￾ciency, liver disease, and nephrosis. SG will increase about
0.004 units for every 1% change in glucose concentration
and about 0.003 units for every 1% change in protein.
Fixed SG (isosthenuria) around 1.010 is observed in severe
renal damage, in which the kidney excretes urine that is
iso-osmotic with the plasma. This generally occurs after an
initial period of anuria because the damaged tubules are
unable to concentrate or dilute the glomerular filtrate.16
pH
Determinations of urinary pH must be performed on
fresh specimens because of the significant tendency of
urine to alkalinize on standing. Normal urine pH falls
within the range of 4.7 to 7.8. Acidity in urine (pH < 7.0)
is primarily caused by phosphates, which are excreted
as salts conjugated to Na+, K+, Ca2+, and NH4

• . Acidity
  also reflects the excretion of the nonvolatile metabolic
  acids pyruvate, lactate, and citrate. Owing to the Na+/H+
  exchange pump mechanism of the renal tubules, pH
  (H+ concentration) increases as sodium is retained.
  Pathologic states, in which increased acidity is observed,
  include systemic acidosis, as seen in diabetes mellitus,
  and renal tubular acidosis (RTA). In RTA, the tubules
  are unable to excrete excess H+ even though the body is
  in metabolic acidosis, and urinary pH remains around 6.
  Alkaline urine (pH > 7.0) is observed postprandially
  as a normal reaction to the acidity of gastric HCl dumped
  into the duodenum and then into the circulation or fol￾lowing ingestion of alkaline food or medications. Urinary
  tract infections and bacterial contamination also will
  alkalinize pH. Medications such as potassium citrate and
  sodium bicarbonate will reduce urine pH. Alkaline urine
  is also found in Fanconi syndrome, a congenital gener￾alized aminoaciduria resulting from defective proximal
  tubular function.
  Chemical Analyses
  Routine urine chemical analysis is rapid and easily per￾formed with commercially available reagent strips or
  dipsticks. These strips are plastic coated with different
  reagent bands directed toward different analytes. When
  dipped into urine, a color change signals a d
  eviation
  from normality. Colors on the dipstick bands are
  matched against a color chart provided with the reagents.
  Automated and semiautomated instruments that detect
  to green color is a result of bile pigment oxidation. Red
  and brown after standing are due to porphyrins, whereas
  reddish-brown in fresh specimens comes from hemoglo￾bin or red cells. Brownish-black after standing is seen in
  alkaptonuria (a result of excreted homogentisic acid) and
  in malignant melanoma (in which the precursor mela￾nogen oxidizes in the air to melanin). Drugs and some
  foods, such as beets, may also alter urine color.
  Odor
  Odor ordinarily has little diagnostic significance. The
  characteristic pungent odor of fresh urine is due to vola￾tile aromatic acids, in contrast to the typical ammonia
  odor of urine that has been allowed to stand. Urinary
  tract infections impart a noxious, fecal smell to urine,
  whereas the urine of diabetics often smells fruity as a
  result of ketones. Certain inborn errors of metabolism,
  such as maple sugar urine disease, are associated with
  characteristic urine odors.
  Turbidity
  The cloudiness of an urine specimen depends on pH and
  dissolved solids composition. Turbidity generally may
  be due to gross bacteriuria, whereas a smoky appearance
  is seen in hematuria. Thread-like cloudiness is observed
  when the specimen is full of mucus. In alkaline urine,
  suspended precipitates of amorphous phosphates and
  carbonates may be responsible for turbidity, whereas in
  acidic urine, amorphous urates may be the cause.16
  Volume
  The volume of urine excreted indicates the balance between
  fluid ingestion and water lost from the lungs, sweat, and
  intestine. Most adults produce from 750 to 2,000 mL every
  24 hours, averaging about 1.5 L per person. Polyuria is
  observed in diabetes mellitus and insipidus (in insipidus,
  as a result of lack of ADH), as well as in chronic renal
  disease, acromegaly (overproduction of the growth hor￾mone somatostatin), and myxedema (hypothyroid edema).
  Anuria or oliguria (