Urinalysis is a clinical screening test which can identify medical diseases that have gone unnoticed as they do not produce striking signs and symptoms.
Examples include Diabetes mellitus and insipidus, glomerulonephritis, and chronic urinary tract infections (UTIs).
Perform urinalysis on a fresh catch specimen, the first void of the day may be preferred as it is more concentrated but the time for routine testing is not important. The test should include:
- Observation of colour, clarity and smell
- Specific Gravity
Clinical practice point. Study the information leaflet supplied with the urinalysis strips, the method of use, how to read, record and interpret the results. Check the strips are in date before use.
We will now look at each of the tests in greater detail.
Colour, clarity and smell
Normal urine should be pale yellow to gold (sometimes described as pale straw colour). It should be clear, not cloudy and should not smell strongly of any odour.
Urine that is dark indicates very concentrated urine, possible liver disease (from bile in urine) or may contain blood.
Cloudy urine is often caused by protein molecules and/or bacteria, pus and blood, usually from infection in the urinary tract.
Strongly smelling urine may be the result of concentrated urine from dehydration but is often a sign of infection. A ‘fishy’ smell is often described in the presence of urinary tract infection.
Certain foods can give urine an odour, such as asparagus or cabbage and others can change the colour of urine eg beetroot, high amounts of carrots and oranges
The presence of leucocytes indicates, pyuria, a condition where the urine contains white blood cells or pus and is a sign of bacterial urinary tract infection.
The presence of nitrites indicates the presence of coliform bacteria.
The presence of protein in urine is known as proteinuria and it indicates renal infection or diseases.
Proteins are large molecules and do not filter through the glomerulus into the urine. Presence indicates renal infection or diseases that have a secondary effect in the kidneys eg hypertension, diabetes mellitus, hypothyroidism.
Urine pH is used to classify if urine is acidic or alkaline. Normal urine pH is slightly acidic with a pH of 5 or 6. A pH of 7 is neutral and above 7 is alkaline.
A highly acidic urine output occurs with dehydration, starvation, diarrhoea, uncontrolled diabetes and respiratory conditions.
A highly alkaline urine occurs with urinary tract obstruction due to kidney stones, chronic renal failure and respiratory conditions.
Urine is usually more acidic in the morning (reduced breathing in sleep causes respiratory acidosis).
A diet rich in vegetables and citrus fruit raises the pH producing an alkaline urine, vegetarians are likely to have alkaline urine.
A diet high in animal proteins, meat, milk and cheese, will keep urine acidic.
Bacteria causing urinary tract infection or bacterial contamination will produce alkaline urine.
Blood in urine, haematuria, can be caused by urinary tract-specific problem, trauma, stones, infection, malignancy. Painless haematuria may be a sign of urinary tract malignancy and warrants cytological investigation.
Specific Gravity (SG) measures the concentration of the urine.
- A SG under 1.010 indicates hydration
- A SG above 1.030 indicates dehydration
The presence of ketone bodies in urine, ketonuria, occurs with carbohydrate starvation, high protein diets and type 1 diabetes mellitus.
The production of ketones is the normal response to a shortage of glucose. The ketones come from the breakdown of fatty acids to provide energy. Acetone is also produced as the fats burn to provide energy, which gives the fruity-sweet smell to the urine.
It is not normal to find glucose in the urine. Although glucose filters into the glomerulus it is normally absorbed from the renal tubules back into the blood.
Presence of glucose in the urine is glycosuria and it is nearly always caused by elevated blood glucose levels. Diabetes mellitus is often diagnosed by urine testing.
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