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1392 Urine Protein/Creatinine Ratio Urine Specific Gravity (USG)

Reference Interval Next Diagnostic Steps to Consider Relative Cost: $ (reported as part of
Dogs and cats: 6.0 to 7.5; however, urine pH if Levels are Low urinalysis)
VetBooks.ir and alkalinuria are not always associated with signs. Evaluate for an acid-base disturbance with Pearls
Consider history (including drugs) and clinical
can change with food or medications. Aciduria
• Alkalinuria may cause false proteinuria via
a blood gas analysis and biochemistry panel.
disease.
dipstick reagent pad.
Causes of Abnormally High Levels Drug Effects • Reagent test strips measure pH in increments
Alkalinuria: alkaloses, urea degradation (i.e., Loop and thiazide diuretics promote aciduria of 0.5 between the range of 5.0 and 8.5.
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effect of storage, urease-containing bacteria), secondary to potassium-wasting (i.e., H is AUTHOR: Shannon D. Dehghanpir, DVM, MS, DACVP
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distal renal tubular acidosis excreted in exchange for K retention). EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
Next Diagnostic Steps to Consider Lab Artifacts
if Levels are High Pigmenturia can interfere with interpretation.
Ensure use of fresh urine. Evaluate for urinary Prolonged storage of urine may raise pH.
tract infection via urine sediment and bacterial
culture. Specimen Collection and Handling
Perform with fresh urine as urine alkalinizes
Causes of Abnormally Low Levels over time.
Aciduria: acidoses, paradoxic aciduria (second-
ary to hypochloremic metabolic alkalosis),
proximal renal tubular acidosis, hypokalemia

Urine Protein/Creatinine Ratio

Definition Reference Interval Specimen Collection and Handling
A quantitative measurement of protein in • Healthy dogs and cats: < 0.2 Perform on fresh urine with inactive sediment.
the urine that is unaffected by urine concentra- • Borderline proteinuria: 0.2-0.5 (dogs) and Urine can be collected via free-catch or cysto-
tion 0.2-0.4 (cats) centesis. Pooled samples are preferable to single
• Proteinuria: > 0.5 (dogs) and > 0.4 (cats) (“spot”) samples. Urine samples can be collected
Synonyms by the pet owner and stored frozen before submis-
UPC, UP:UC Causes of Abnormally High Levels sion; the veterinarian can combine equal volumes
• Pre-renal (overflow) proteinuria: hemo- from each urine sample for analysis. Hospital
Physiology globinuria, myoglobinuria, Bence Jones collection (versus home collection) may increase
Most serum proteins cannot pass through proteinuria results, likely due to transient stress proteinuria.
the glomerular filtration barrier due to their • Renal proteinuria: glomerular disease (e.g.,
large size. Small proteins that pass through the glomerulonephritis, amyloidosis, glomeru- Relative Cost: $$
glomerulus are typically reabsorbed by the renal losclerosis), tubular disease (e.g., Fanconi
tubules. Thus, sources of proteinuria include syndrome, acute kidney injury), transient Pearls
increased delivery of small proteins to the proteinuria (secondary to fever, stress, exercise) • A UPC > 2 is typically associated with
glomerulus, glomerular disease, tubular disease, • Post-renal proteinuria: inflammation or glomerular disease (assuming pre- and
or post-glomerular sources of protein (i.e., hem- hemorrhage of the urogenital tract post-renal causes excluded).
orrhage or inflammation of the urogenital tract). • Proteinuria secondary to tubular disease is
The UPC is calculated by dividing the urine Next Diagnostic Steps to Consider often mild (UPC < 2).
total protein (mg/dL) by the urine creatinine if Levels are High • Do not perform UPC in the face of recog-
(mg/dL). As the renal excretion of creatinine • Exclude pre-renal (e.g., hemoglobinuria, nized lower urinary tract inflammation or
is relatively constant, any increase in the UPC myoglobinuria) or post-renal (e.g., hema- when gross hematuria is present.
reflects increased protein excretion. UPCs are turia, pyuria, bacteriuria) protein sources. • UPC has replaced 24-hour urine quantifica-
generally performed after documentation of • If first abnormal UPC, repeat testing to tion for assessment of proteinuria.
proteinuria via urine dipstick in absence of a exclude transient cause.
pre-renal or post-renal cause. • See pp. 51 and 390. AUTHOR: Shannon D. Dehghanpir, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP

Urine Specific Gravity (USG)

Definition Physiology Urine solute concentration is measured by urine
The measurement of urine solute concentration Glomerular filtrate is modified by the renal specific gravity (USG) or osmolality (the gold
based on the density of urine compared to water tubules through reabsorption or secretion of standard) and is used to assess the concentrat-
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water or solutes (e.g., urea, creatinine, K ). ing ability of the kidneys. USG is typically
Synonym Reabsorption of water requires functional antidi- measured indirectly via refractometry. Always
Urine density uretic hormone and medullary hypertonicity. interpret the USG in conjunction with the
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