Liquid gold part 1 - The physical and chemical examination of urine provides information for much more than just the urinary system

Introduction

Complete urinalysis should be performed every time a need to evaluate the renal system exists. However, the complete urinalysis is not only of value for evaluation of the renal system. The urinalysis can provide information about other body organ systems like the liver as well as help characterize underlying systemic acid-base abnormalities, the severity of diabetes and diabetic ketoacidosis as well as assisting in characterizing various hematologic abnormalities like hemolytic disease.

Routine urinalysis can easily and accurately be performed in a veterinary practice. There are different components of a complete urinalysis. The physical examination of the urine collected includes crude but important gross inspection of the urine. The chemical examination primarily consists of multiple tests performed on the classic dry reagent strip testing commonly known as the “Dip Stick” test. The microscopic examination consists of evaluation of the formed elements of a urine specimen and is something that should be performed in a short time following the collection of the urine specimen.

Urinalysis - physical examination

The gross inspection of a urine specimen can provide significant information regarding any identifiable disease process involving the urinary system. Some of the more common or useful physical features of urine specimens are outlined briefly below.

Color

Color of the urine can provide potential insight into the various formed elements of the urine. For example, a red urine is most commonly seen when erythrocyte associated pigment, hemoglobin, is present in the specimen. This could include either cell-free hemoglobin present because of severe hemoglobinemia with subsequent hemoglobinuria or due to hemolysis of any formed erythrocytes present in the urine specimen. Additionally, red urine could merely be colored because of the presence of intact erythrocytes. In this latter situation, the supernatant of the urine should be clear following centrifugation where erythrocytes are forced into a pellet in the centrifuge tube. Brown-red colored urine may be seen associated with myoglobinuria or oxidized hemoglobinuria. Dark yellow colored urine may be seen associated with marked bilirubinuria.

Turbidity

Turbidity of any type of a fluid specimen is related to particular matter in that specimen. This particular matter could be lipid droplets in something like a lipemic serum or plasma specimen, intact cells like a whole blood specimen, or any other type of particular matter. Normal urine specimens typically are clear. With turbid urine specimens, the more commonly particles that give the urine a turbid appearance include bacteria, inflammatory cells, erythrocytes, and crystals.

Odor

A strong ammonia odor to a urine specimen may suggest breakdown of urea, which should be in relatively high concentrations in a normal urine specimen, into ammonia by urea splitting bacteria. This simple physical feature of a urine specimen may provide immediate information regarding underlying bacterial infection of the urinary tract.

Specific Gravity

Specific gravity is commonly estimated from the refractive index of a urine specimen with the use of a refractometer. The specific gravity is predicated upon the presence of a concentration of small solutes. It is used as a simple measure of the ability of the kidney to concentrate or dilute a urine specimen and in conjunction with the measurement of serum urea nitrogen or creatinine, proves essential in the classification / identification of “renal failure”. Selected solutes in high concentration that normally should not be present in typical urine specimens may contribute slightly to the specific gravity / refractive index of the urine. The more commonly encountered “abnormal” solutes that may play this role include glucose and protein in relatively high concentrations.

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