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 (pH7.0) 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 (pH7.0) 
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 (