Urinalysis

Author's note: This article is a very brief overview of the medical procedure called urinalysis. It is not intended to provide or supersede professional medical advice.


Whenever a medical professional orders a urine sample from a patient, the collected urine is often sent directly to a lab for a procedure called urinalysis. Depending on the physician's orders, the lab technologist will examine everything from the color and temperature down to the most microscopic crystal formations or blood cells. Urinalysis can detect pregnancy, recreational drug use, diabetes, kidney diseases or evidence of infections elsewhere.


One of the first elements a lab technologist will check during urinalysis is color. Normal urine should be a pale yellow to amber color, but anything closer to the red spectrum can be a warning flag. The discoloration may only be caused by eating red beets or ingesting food coloring, but it can also be related to excessive shedding of red blood cells. Cloudiness may indicate crystal formation or an infection. Dark yellow or orange urine is usually a sign of extreme dehydration.


After the color and clarity have been noted, another urinalysis test may measure specific gravity. Roughly speaking, this would be the relative 'thickness' of the urine sample. Normal urine is only slightly denser than pure water because of the additional minerals and cell tissues dissolved in it. If the urinalysis reveals a significantly higher specific gravity, the patient may have excessive levels of glucose. This could indicate a blood sugar imbalance requiring immediate medical attention.


Today urinalysis can be performed manually with a dipstick or via an automated machine. Here are a few pointers on urinalysis interpretation:


Urinalysis:





Smell:

The normal smell of urine can be described as urinoid. Other smells of interest include:



Colour:

Normal urine colour is often described as straw, yellow or amber. This colour may be altered by medications, food sources or disease.


Vitamin tablets often result in a bright yellow urine, as does the presence of bilirubin (a bile pigment).


Red urine may be due to blood, haemoglobin, or beetroot.


Iron supplements may cause a dark brown specimen, as might amounts of prophobilin or urobilin (a chemical produced in the intestines).


Normal urine is also transparent. Turbid or cloudy urine may result from infection the presence of blood cells, bacteria or yeast (eg Candida).


A foamy urine may indicate either the presence of glucose or protien.


Leukocytes:

Detects white cells in the urine (pyuria) which is associated with urinary tract infection.


Nitrites:

Nitrites are formed by the breakdown of urinary nitrates. This us usually caused by Gram-negative and some Gram-positive bacteria.


So the presence of nitrites suggests bacterial infection such as E.coli, Staphylococcus and Klebsiella.


Commonly found during a urinary tract infection.


Urobilinogen:

Normally present in the urine in small quantity. Less than 1% of urobilinogen is passed by the kidneys the remainder is excreted in the faeces or transported back to the liver and converted into bile.


Raised levels may be due to:



Protein:

This is measuring the amount of albumin in the urine. Normally there should be no detectable quantities.


Elevated protein levels are known as proteinuria. Albumin is one of the smaller protiens, and if the kidneys begin to dysfuncion it may show an early sign of kidney disease.


Other conditions which may lead to protein in the urine include:



pH:

Measures the hydrogen ion concentration of the urine.


It is important that a fresh sample be used as urine becomes more alkaline over time as bacteria convert urea to ammonia (which is very alkaline).


Urine is normally acidic but its normal pH ranges from 4.5 to 8.


Low pH (acidic):

Foods such as acidic fruits (cranberries) can lower the pH, as can a high protein diet.


As urine generally reflects the blood pH, metabolic or respiratory acidosis can make it more acidic.


Other causes of acidic urine include diabetes, diarrhoea and starvation.


High pH (alkaline):



Haematuria:

Classified as microscopic or macroscopic. Microscopic means that the blood is not visible with the naked eye.


Blood may be present in the urine following trauma, smoking, infection, renal calculi or strenuous exercise.


It may also be present with:








The presence of myoglobin (myoglobinuria) after muscle injury will also cause the reagent strip to indicate blood.


Specific Gravity:

The specific gravity (SG) of urine signifies the concentration of dissolved solutes and reflects the effectiveness of the renal tubules to concentrate it (when the body needs to conserve fluid). If there were no solutes present the urines SG would be 1.000, the same as pure water.


The SG of urine is around 1.010 but can vary greatly:


Decreased SG may be due to:



Increased SG may be due to:



It also reflects a high solute concentration which may be from glucose (diabetes or IV glucose) or protein.


Ketones:

Not normally found in the urine, ketones are produced during fat metabolism.


Presence of ketones may indicate:



Bilirubin:

Produced as a by-product during the degradation of RBC in the liver and normally excreted in the bile. Once in the intestine it is excreted in the faeces (as stercobilin) or by the kidneys (as urobilinogen).


Presence of bilirubin in the urine may therefore indicate:



Glucose:

Glucose is not normally present in the urine.


Once the level of glucose in the blood reaches a renal threshold the kidneys begin to excrete it into the urine in an attempt to decrease the blood concentration. So high blood concentrations lead to glucosuria, as does conditions that may reduce this renal threshold.