Performing a Urinalysis
Posted: Tuesday, November 30th, 2021 | Updated: Thursday, August 25th, 2022
Posted: Tuesday, November 30th, 2021 | Updated: Thursday, August 25th, 2022
Sample Collection
There are three ways to collect urine from a patient for evaluation. Free catch samples are easily obtained, but may include contamination from cells, bacteria, and various debris. Catheterization of the urinary bladder may be obtained in a sterile manner, however contamination may still occur. Cystocentesis of the urinary bladder tends to provide the best sample for analysis. Samples obtained via cystocentesis can be sent out for culture as well. Patients who are coagulopathic should not have their urine obtained via this method for risk of ongoing hemorrhage
Obtaining a Diagnostic Sample
Samples collected for urinalysis and culture via cystocentesis may be obtained using a 22 gauge 1 to 1.5 inch needle and a 6 to 12 ml syringe. The area of sampling should be cleaned with the appropriate solution prior to entry into the abdomen. Trained personnel may sample urine via the blind-stick method or via an ultrasound guided method. The latter is generally safer
Sample Handling and Storage
Collected urine should ideally be analyzed within the hour because cells and casts may deteriorate. Samples that can't be analyzed within the hour should be stored in a glass red top tube without any additives and be refrigerated. Samples should be observed within 6 hours of refrigeration
Urine Color
Normal: Pale yellow, yellow, amber
Red: Erythrocytes, hemoglobin, myoglobin
Red-Brown or Black: Erythrocytes, hemoglobin, myoglobin, methemoglobin
Yellow-Orange: Bilirubin
Yellow-Green or Brown: Bilirubin or Biliverdin
Note that myoglobin is usually caused by muscle breakdown or injury. Erythrocytes are simply red blood cells indicating that bleeding is present in some degree. Hemoglobin is typically seen with the lysis of red blood cells. When the urine is spun down for analysis, any erythrocytes will form a clump at the bottom of the tube being spun. If hemoglobinuria is present, the urine will stay red in color after being spun. Methemoglobin in the urine is usually due to ingestion of a toxin and the pigment will stay red-brown once spun
Spinning Urine Down for Evaluation of Sediment
Place urine in a centrifuge tube and run the sample at 1500 rpm for 5 minutes. The sediment should be visible at the bottom of the tube once the cycle is complete. Remove the majority of the supernatant and then remix the remaining sample by flicking or tapping the tube gently. Place a drop of the sediment on a microscope slide for evaluation. Samples may be evaluated fresh with a slide cover, stained or unstained. They may also be left to air dry and stained using Diff-Quik
Microscopic Evaluation
Briefly scan the slide at 10x to visualize any gross abnormalities such as some casts or to count the epithelial cells. This is the low power field or LPF. Use the 40x power, or high power field (HPF), to evaluate cells and crystals. Bacteria may also be visualized at this field on a wet mounted slide, although evaluation at 100x with oil immersion is best suited on a dry mounted slide. Estimate the number of cells or crystals by counting the number found in 10 fields and taking the average. Up to 5 RBC and up to 5 WBC per HPF may be present in healthy animals
For information regarding urine specific gravity (USG) CLICK HERE
There are three ways to collect urine from a patient for evaluation. Free catch samples are easily obtained, but may include contamination from cells, bacteria, and various debris. Catheterization of the urinary bladder may be obtained in a sterile manner, however contamination may still occur. Cystocentesis of the urinary bladder tends to provide the best sample for analysis. Samples obtained via cystocentesis can be sent out for culture as well. Patients who are coagulopathic should not have their urine obtained via this method for risk of ongoing hemorrhage
Obtaining a Diagnostic Sample
Samples collected for urinalysis and culture via cystocentesis may be obtained using a 22 gauge 1 to 1.5 inch needle and a 6 to 12 ml syringe. The area of sampling should be cleaned with the appropriate solution prior to entry into the abdomen. Trained personnel may sample urine via the blind-stick method or via an ultrasound guided method. The latter is generally safer
Sample Handling and Storage
Collected urine should ideally be analyzed within the hour because cells and casts may deteriorate. Samples that can't be analyzed within the hour should be stored in a glass red top tube without any additives and be refrigerated. Samples should be observed within 6 hours of refrigeration
Urine Color
Normal: Pale yellow, yellow, amber
Red: Erythrocytes, hemoglobin, myoglobin
Red-Brown or Black: Erythrocytes, hemoglobin, myoglobin, methemoglobin
Yellow-Orange: Bilirubin
Yellow-Green or Brown: Bilirubin or Biliverdin
Note that myoglobin is usually caused by muscle breakdown or injury. Erythrocytes are simply red blood cells indicating that bleeding is present in some degree. Hemoglobin is typically seen with the lysis of red blood cells. When the urine is spun down for analysis, any erythrocytes will form a clump at the bottom of the tube being spun. If hemoglobinuria is present, the urine will stay red in color after being spun. Methemoglobin in the urine is usually due to ingestion of a toxin and the pigment will stay red-brown once spun
Spinning Urine Down for Evaluation of Sediment
Place urine in a centrifuge tube and run the sample at 1500 rpm for 5 minutes. The sediment should be visible at the bottom of the tube once the cycle is complete. Remove the majority of the supernatant and then remix the remaining sample by flicking or tapping the tube gently. Place a drop of the sediment on a microscope slide for evaluation. Samples may be evaluated fresh with a slide cover, stained or unstained. They may also be left to air dry and stained using Diff-Quik
Microscopic Evaluation
Briefly scan the slide at 10x to visualize any gross abnormalities such as some casts or to count the epithelial cells. This is the low power field or LPF. Use the 40x power, or high power field (HPF), to evaluate cells and crystals. Bacteria may also be visualized at this field on a wet mounted slide, although evaluation at 100x with oil immersion is best suited on a dry mounted slide. Estimate the number of cells or crystals by counting the number found in 10 fields and taking the average. Up to 5 RBC and up to 5 WBC per HPF may be present in healthy animals
For information regarding urine specific gravity (USG) CLICK HERE
Sources:
Beatty, Sarah. "In-Clinic Preparation and Evaluation of Urine Dry-Mount Samples" Today's Veterinary Nurse. July/August 2022.
Rizzi, E. Theresa. "Urinalysis in Companion Animals Part 1: Collection, Sample Handling, & Initial Evaluation." Today's Veterinary Practice, March/April 2014, https://todaysveterinarypractice.com/wp-content/uploads/sites/4/2016/06/T1403C07.pdf
Rizzi, E. Theresa. "Urinalysis in Companion Animals, Part 2: Evaluation of Urine Chemistry & Sediment." Today's Veterinary Practice, May/June 2014, https://todaysveterinarypractice.com/urinalysis-in-companion-animals-part-2-evaluation-of-urine-chemistry-sediment/
Beatty, Sarah. "In-Clinic Preparation and Evaluation of Urine Dry-Mount Samples" Today's Veterinary Nurse. July/August 2022.
Rizzi, E. Theresa. "Urinalysis in Companion Animals Part 1: Collection, Sample Handling, & Initial Evaluation." Today's Veterinary Practice, March/April 2014, https://todaysveterinarypractice.com/wp-content/uploads/sites/4/2016/06/T1403C07.pdf
Rizzi, E. Theresa. "Urinalysis in Companion Animals, Part 2: Evaluation of Urine Chemistry & Sediment." Today's Veterinary Practice, May/June 2014, https://todaysveterinarypractice.com/urinalysis-in-companion-animals-part-2-evaluation-of-urine-chemistry-sediment/