Urinalysis: dipstick analysis

• Changes in chemical and physical characteristics of urine occur in many diseases and include urinary tract disease, hepatic disease, hematological disorders, endocrinopathy, neoplasia, musculoskeletal disease and hepatic encephalopathy.
• These changes in characteristics can predict disease.
• Therefore, used as a screening test in any ill patient.
  Always do complete urinalysis including sediment examination.

In combination

• With other tests, eg blood glucose Blood biochemistry: glucose , fructosamine Blood biochemistry: fructosamine for monitoring glucose control treatment of diabetes mellitus Diabetes mellitus.

• Diagnosis of diabetes mellitus.

Other points

• Dipstick urine specific gravity should be ignored ( it is inaccurate for animal urine); use refractometer method.

• Urine collected by:
  • Cystocentesis Cystocentesis.
  • Catheterization Urethral catheterization: female Urethral catheterization: male.
  • Midstream free flow sample Urine collection: freeflow.

• A few drops to 1 ml.
• Standard volume of 4-5 ml preferred.

Cystocentesis

• See technique Cystocentesis.
• Use a 10 ml sterile syringe and a 1.5 inch 21-25G needle.
• With the animal standing or in lateral recumbency, palpate and direct bladder towards abdominal wall.
• Needle is introduced through abdominal wall. Direct needle point caudodorsally towards the bladder neck.
• If bladder is less obviously palpable, place animal in dorsal recumbency and direct needle through midline in the bitch or lateral to the penis in the dog at the level of the last mammary gland. Direct needle caudodorsally.

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.

Early morning sample

• Advantage: concentrated with higher yield of cells, casts and bacteria.
• Disadvantage: less likely to reveal hyperglycemic glucosuria than a 3 hour post-prandial sample. Cells may be degenerated.

Recently formed sample

• Advantage: cytologic detail superior.
• Disadvantage: may be insufficiently concentrated to evalute renal function as well as causing lysis of red and white blood cells.

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

• The longer the delay between collection and analysis, the less reliable the results.
• Temperature above 8°C for longer than 30 minutes results in artefacts.
• Must not transport without preservative.
• Package according to Post Office regulations Transportation of diagnostic specimen.

• Determine specifc gravity by refractometer.
  Dipstick specific gravity does not correlate well with refractometry.
• 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.

• Can be performed in-house by most veterinary practices.
• All external laboratories.

Sensitivity

• Low to high.

Specificity

• Low to moderate.

• Urine specific gravity reading on dipstick is unreliable.

• Standardized approach for every analysis results in consistent findings and allows the technician to develop experience.

pH

• 5.5-7.0.
  Some normal dogs may be outside this range.

Protein

• Myelomas will not cause a positive protein reaction on dipstick.
• Normal ranges:
  Chemical determination is more accurate than dipstick estimates. Check all abnormal results by other methods.

Glucose

• If SG <1.020: negative.
• If SG >1.035: <30 mg/dl.
• Urine protein:urine creatinine ratio <0.6.

• Negative.

Ketones

• Negative.

Bilirubin

• If SG >1.020: trace.

Urobilinogen

• Trace.

Blood

• Negative.

Nitrite

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

• Not using fresh urine.
• Outdated dipstick (beyond expiration date).
• Incorrect storage of dipstick.
• Urine not at room temperature.
• Reading dipstick at incorrect time.
• Using a collection technique other than cystocentesis.
• Not being consistent in analysis (technique, timing, volume).

pH

• Increase:
  • Sample standing open at room temperature for few hours (loss of CO2).
  • Furosemide Furosemide at therapeutic dose.
• Decrease:
  • Ammonium chloride.
  • Ascorbic acid Vitamin C.

Protein

• Increase:
  • Chlorhexidine Chlorhexidine.
  • Moisture on dipstick during storage.
  • Prolonged contact of dipstick with excessive amounts of urine.
  • Alkaline urine (>9).

Glucose

• Increase:
  • Intravenous fluids containing dextrose.
  • Aminoglycoside toxicity Gentamicin.
  • Fanconi's syndrome Fanconi's syndrome.
  • Renal glycosuria.
• Decrease:
  • Refrigerated urine.
  • Large amounts of ascorbic acid Vitamin C.
  • Tetracycline Tetracycline (ascorbic acid in formulation).
  • Salicylates Acetyl salicylic acid.
  • Ketones.
  • Low urine pH.

Ketones

• Negative.

Bilirubin

• Increase:
  • Large amounts of phenothiazines Therapeutics: nervous system.
• Decrease:
  • Ascorbic acid Vitamin C.
  • Aspirin Acetyl salicylic acid.
  • Prolonged exposure to ultraviolet light.​

Urobilinogen

• Increase:
  • Acetazolamide Acetazolamide.
  • Bilirubin.
  • Sulfonamide.
• Decrease:
  • Prolonged exposure to light.​

Hematuria

• Increase:
  • Trauma during sampling.
  • Contamination with vaginal/preputial secretion.
• Decrease:
  • Hemolysis.
  • Hyposthenuric.
  • Very acid urine.
  • Very alkaline urine.

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.