Urinalysis: dipstick

• Changes in chemical and physical characteristics of urine occur in urinary tract and systemic disease and trauma.
• Such changes can be detected by the reaction of specific components with reagents impregnated in dipstick pads which produce characteristically graded color changes.
• Results are qualitative and depend on subjective interpretation of user.

Alone

• Monitoring glucose control treatment of diabetes mellitus Diabetes mellitus (crude method).

In combination

• With other laboratory tests for investigation of polyuria/polydipsia.
• Serum creatinine Blood biochemistry: creatinine and urine specific gravity (refractometer) Urinalysis: specific gravity to assess renal function.
• Serum bile acids Blood biochemistry: bile acid and serum urea Blood biochemistry: urea to investigate hepatic encephalopathy Hepatic encephalopathy due to portocaval shunt Congenital portosystemic shunt (CPSS).
• Serum glucose Blood biochemistry: glucose to confirm diabetes mellitus.
• Culture and sensitivity Urinalysis: culture and sensitivity to investigate upper and lower urinary tract infection Cystitis: bacterial.

• Ultrasonography Ultrasonography: bladder and urinary tract to investigate hematuria.
• Hematology Hematology: complete blood count (CBC) in severe hemolytic disease.

• Hematology and biochemistry to investigate endocrinopathy.

Other points

• Refractometer method Urinalysis: specific gravity preferred for specific gravity measurement.

• Cystocentesis Cystocentesis.
• Catheterization Urethra: catheterization.
• Free flow urine sample Urine collection: freeflow.

• Standard volume of 4-5 ml preferred.

Precautions

• Trauma during collection may contaminate sample.
• Delay between collection and analysis   →   less reliable results.
• Sample standing for >30 minutes must be refrigerated (2-8°C).
• Urine must be at room temperature before analysis.
• Protect sample from bright light.

Timing of test

• The composition of urine varies throughout the day.
• Sample for screening test at any time of day.

Sample storage

• Urine can be refrigerated at 2-8°C for a few hours (maximum 12 hours).
• If sample is to be stored, divide into two containers, add preservative (boric acid tablet or 10% formalin) to one and refrigerate both.
• The sample with preservative is for sediment examination. The sample with no preservative is for dipstick (chemical) analysis.
• Specimen for bacteriologic culture should be in sterile container without preservative.

Sample transport

• Standard mailing times.
• Package according to mailing regulations Transportation of diagnostic specimen.

• Rapid, complete immersion of the dipstick with immediate shaking off of excess urine as well as holding the dipstick level is needed to avoid run-off between pads.
• Compare the color change of dipstick to the reference range at the correct time specified on product.
• Determine specific gravity by refractometer.
  Dipstick specific gravity does not correlate well with refractometry.

• Can be performed in-house.
• All external laboratories.

Sensitivity

• Low to high.

Specificity

• Low to moderate.

• ?Reliable reading of specific gravity of urine.

• Interpretation of color change is subjective, so routine use of the same technician/vet will result in more consistent results.

pH

• Usually acid, mean 6.0, range 5.0-9.0.
  Vegetable and cereal diets can result in alkaline urine.

Protein

• Trace.

Glucose

• Negative.

Ketones

• Negative.

Bilirubin

• Negative.
• If specific gravity >1.020: trace.

Blood

• Negative.

Nitrite

• Negative (unreliable in animals for screening for bacteria because of large number of false negative tests).

• pH  Urinalysis: pH.
• Proteinuria Urinalysis: protein.
• Glucosuria Urinalysis: glucose.
• Ketonuria Urinalysis: ketone.
• Bilirubinuria.
• Urobilinogen Urinalysis: urobilinogen.
• Hematuria Urinalysis: blood.
• Nitrituria Urinalysis: nitrate.

• Not using fresh urine.
• Incorrect storage of dipstick
• Urine not at room temperature.
• Reading dipstick at incorrect time.
• Using a collection technique other than cystocentesis.
• Inconsistent technique.
• Dipstick too old (past expiry date).

pH

• Increase: sample standing open at room temperature for few hours (loss of CO2), furosemide Furosemide at therapeutic dose, contamination with urease-producing bacteria (distal urinary tract or environment), detergents or disinfecting agents in collecting containers.
• Decrease: ammonium chloride Ammonium chloride, ascorbic acid Vitamin C.

Protein

• False positive: chlorhexidine Chlorhexidine or other quaternary ammonium compounds, presence of urease-producing bacteria, prolonged immersion of dipstick (   →   loss of buffer), administration of alkalinizing drugs.
• False negative: failure to detect Bence-Jones proteins (associated with myeloma), acidification of urine following collection.

Glucose

• Increase: intravenous fluids containing dextrose, aminoglycoside toxicity.
• Decrease: refrigerated urine, large amounts of ascorbic acid Vitamin C, tetracycline Tetracycline (ascorbic acid in formulation), salicylates Acetyl salicylic acid, ketones, low urine pH, bacteria.

Ketones

• None.

Bilirubin

• Increase: large amounts of phenothiazines Acepromazine maleate.
• Decrease: ascorbic acid, aspirin Acetyl salicylic acid, prolonged exposure to ultraviolet light.

Urobilinogen

• False positives common - often indicate strips are out of date or have been stored incorrectly.

Hematuria

• Increase: trauma during sampling, contamination with vaginal/preputial secretion.
• Decrease: hemolysis occurs in hyposthenuric, very acid urine, very alkaline urine.
  Must interpret with urine sediment examination.

Nitrite

• Increase: phenazopyridine.
• Decrease: frequent voiding, ascorbic acid Vitamin C.

Refereed papers

• Recent references from VetMedResource and PubMed.
• Brobst D (1989) Urinalysis and associated laboratory procedures. Vet Clin North Am Small Anim Pract 19 (5), 929-949.
• McCaw D L, Fleming E J & Mikiciuk M G (1989) Interpreting the results of urinalysis - a key to diagnosing renal disorders. Vet Med 84 (3), 281-286.

Other sources of information

• Kaneko J J (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Eds: Harvey J W & Bruss M L. Academic Press, USA.
• Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine Clinical Pathology. 3rd edn. Iowa University Press, USA.