Sorted By Test Name - Mayo Medical Laboratories

UMIC
9316
Reference Values:
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
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1822