Urine Normal Composition
|
Introduction
The testing and evaluation of urine composition is an essential diagnostic indicator for many diseases. It is therefore essential to have an understanding of what is the normal composition of urine.
Normal Urine Volume
Below are the normal urine volumes for the common domestic species. The units are ml/kg/day
Adapted from the Merck Veterinary Manual online reference table entitled Urine Volume and Specific Gravity
The Normal Appearance of Urine
Several pathological conditions can cause macroscopic changes to the urine. It is therefore essential to appreciate the normal appearance of urine. In many of the exotic species the urine has a very differant appearance and therefore use care when applying this to those species.
Colour
In the majority of the domestic species the urine should be yellow in colour. The colour of the urine is very dependant on the urine specific gravity so it is important to account for this. If the urine is more concentrated it will be darker in colour and visa versa as a general rule . Equine urine can become brown if left standing. Discoloured urine should be taken into consideration when carrying out tests which involve a colour change such as dipsticks. The abnormal urine colour could affect the result.
Turbidity
If the urine is not clear then this could indicate a variety of pathological states. In the horse it is normal for it to be turbid due the mucous secreted in the renal pelvis and proximal ureters.
Odour
It is normal for urine to have a slight odour from the ammonia. The odour increases with concentration and in some species such as the cat a pungent urine is normal. However a strong smelling urine could indicate a pathological state
Urine Specific Gravity
Urine specific gravity is measured using a refractometer calibrated for veterinary use. All the domestic species except cats can be measured on a scale calibrated to dog urine. Cats require measurement against their own scale.
Specific gravity relates to the concentration. It is basically a measure of the density of particles in the urine.
Below are the normal urine specific gravities for the common domestic species.
Adapted from the Merck Veterinary Manual online reference table entitled Urine Volume and Specific Gravity
Urine Chemistry
The following are common chemicals or parameters whose levels in urine change in pathological vs normal conditions. It is therefore important to appreciate their normal levels
pH
In dogs and cats an acidc pH is normal. In the ruminants and horses the opposite is true and the urine is alkali. The pH does however vary with diet and medications as well as in pathological states so this needs to be accounted for. The normal range is 5-9
Protein
It is not common to find protein in the urine of normal animals. However it can be normal for small amounts to be found in the urine of dogs with a high specific gravity. Therefore this needs to be taken into account.
Glucose
The presence of glucose in the urine is termed glucosuria and occurs when the level of glucose reaches the renal threshold for glucose reabsorption. It is not normal to find glucose in the urine.
Ketones
It is not normal for ketones to be present in the urine and they are indicative of pathological states
Bilirubin and Urobilinogen
Small amounts of bilirubin can be found in dogs with concentrated urine therefore this needs to be interpreted in light of the urine specific gravity. However as a rule it is not normal to find bilirubin in urine.
Urobilinogen is formed from bilirubin in the intestine and small quantities are normally found in the urine.
Blood
The presence of blood in the urine is not normal and is usually related to a pathological state.
Microscopic Examination of Urine
Uroliths and casts can be seem on microscopic examination. Neither of these are a normal finding.
Bacteria on the other hand are commonly found in small numbers and inhabit the bladder and urethra often without causing any pathology. However high levels tend to mean disease.
Revision
If you feel confident with this material why not try the flash card revision resource for this section.