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UMIC
9316
Descriptive report
Urinalysis, Microscopic, Osmolality, and pH
Clinical Information: The kidney plays a key role in the excretion of by-products of cellular
metabolism and regulation of water, acid-base, and electrolyte balance. Urine is produced by filtration
of plasma in the renal glomeruli followed by tubular secretion and/or reabsorption of water and other
compounds. Abnormalities detected by urinalysis may reflect either urinary tract diseases (eg, infection,
glomerulonephritis, loss of concentrating capacity) or extrarenal disease processes (eg, glucosuria in
diabetes, proteinuria in monoclonal gammopathies, bilirubinuria in liver disease).
Useful For: Screening for urinary tract diseases and some nonrenal diseases
Interpretation: Microscopy: Red blood cells (RBCs), white blood cells (WBCs), renal tubular
epithelial (RTE) cells, casts, squamous cells, parasites, fat, bacteria, and pathologic crystals are
reported. RBCs are almost always indicative of glomerulonephritis. WBC casts are typically an
indication of acute interstitial nephritis or pyelonephritis, but can also be seen in glomerulonephritides
because there is often a component of accompanying interstitial nephritis. Fatty casts and free fat are
often seen in patients with nephrotic syndrome or other glomerular diseases associated with significant
proteinuria. Granular casts are observed in a number of disorders and are thought to be formed from
partially degraded cellular casts, or are protein-derived casts. Hyaline casts are not thought to be
indicative of any disease process, but increased numbers may be seen in concentrated urine specimens.
Waxy casts and broad casts are most often observed in advanced renal failure. Increased numbers of
RTE cells are indicators of renal tubular injury. Increased numbers of RTE cells may be caused by
drugs with renal tubular toxicity (eg, cyclosporine A, aminoglycosides, cisplatin, radiocontrast media,
acetaminophen overdose), interstitial nephritis, hypotension (surgical, sepsis, obstetric complications),
and heme pigments from hemoglobinuria or myoglobinuria from rhabdomyolysis (eg, alcoholism, heat
stroke, seizures, sickle cell trait). Newborns often shed RTE cells in their urine. Based on careful review
of all available published outcome studies with results of detailed hematuria workups within actual
patient populations, a panel from the American Urological Association recommends that patients with
>3 red cells per high-power field in 2 out of 3 properly collected urine specimens should be considered
to have microhematuria, and hence evaluated for possible pathologic causes. However, the panel also
noted that there is no absolute lower limit for hematuria, and risk factors for significant disease should
be taken into consideration before deciding to defer an evaluation in patients with only 1 or 2 red blood
cells per high power field. High-risk patients, especially those with a history of smoking or chemical
exposure, should still be considered for a full urologic evaluation even after 1 properly performed
urinalysis documented the presence of at least 3 red blood cells per high-power field. In certain patients,
even 1 or 2 RBCs per high-powered field might merit evaluation. The presence of squamous cells
suggests that the sample may not have been an optimal clean-catch specimen and could be contaminated
with skin flora. Osmolality: Osmolality is an index of the solute concentration of osmotically active
particles, principally sodium, chloride, potassium, and urea. Glucose can contribute significantly to the
osmolality when present in substantial amounts. The ability of the kidney to maintain both tonicity and
water balance of the extracellular fluid can be evaluated by measuring the osmolality of the urine. More
information concerning the state of renal water handling or abnormalities of urine dilution or
concentration can be obtained if urinary osmolality is compared to serum osmolality. Normally, the
ratio of urine osmolality to serum osmolality is 1.0:3.0, reflecting a wide range of urine osmolality. The
reference ranges are as follows 0-12 months range is 50-750 mOsm/kg. >12 months of age range
is150-1150 mOsm/kg. Please note above the age of 20 years there is an age dependent decline in the
upper reference range of approximately 5 mOsm/kg/yr. pH: Urine pH is affected by diet, medications,
systemic acid-base disturbances, and renal tubular function. pH may affect urinary stone formation. For
example, urine pH 6.0 may
reduce the tendency for uric acid stone formation. Ketones: Produced during metabolism of fat.
Increased ketones may occur during physiological stress conditions such as fasting, pregnancy,
strenuous exercise, and frequent vomiting. Ketones may appear in the urine in large amounts, before
serum ketone is elevated, under the following conditions: - diabetic individuals who are unable to
efficiently utilize glucose due to a lack of insulin - starvation - individuals with other abnormalities of
carbohydrate or lipid metabolism Bilirubin: Bilirubinuria is an indicator of liver disease and biliary tract
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