Urine testing

Written by: 
Dr Paola Accalai

Urine analysis gives important information for the diagnosisThe process of determining which condition a patient may have. of a wide variety of conditions - systemic diseases such as diabetes, for example, as well as those relating specifically to the urinary tract such as urinary tract infectionInvasion by organisms that may be harmful, for example bacteria or parasites. and kidney stones. Pregnancy tests are based on testing the urine for the hormoneA substance produced by a gland in one part of the body and carried by the blood to the organs or tissues where it has an effect. human chorionic gonadotrophin.

This section will provide an overview of the methods of urine collection and the potential relevant test results, as well as the conditions they may point to and follow-up tests that may be needed.

This page covers:

Urine collection

The standard method for urine collection in adults and older children is the mid-stream urine sample or MSU.

You will be given a sterile container to use and sometimes an antiseptic swab to clean the external genitalia (not all practitioners think that this is necessary). Wait until your bladderThe organ that stores urine. feels fairly full.

Start to urinate normally, then after passing a small amount of urine, stop urinating, hold the container so when you start urinating again it is directly under the stream - this is what is meant by a ' mid-stream' sample. Once the container is almost full, hold it aside and finish urinating.

The purpose of this method is to avoid contamination of the urine by skin bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell., which may misleadingly indicate an infectionInvasion by organisms that may be harmful, for example bacteria or parasites. when none is present.

In younger children, in whom this method would be impractical, a clean-catch sample may be taken. This involves keeping the sterile container on hand, with the lid removed, so that a sample may be taken when the child urinates.

Urine collection pads and bags are other options, and urinary catheterA tube used either to drain fluid from the body or to introduce fluid into the body. samples may be used in very young children with a high temperature.

Methods of testing

The main methods of testing are:

Urine dipstick

Reagent strips, commonly referred to as urine dipsticks, are simply dipped into the urine sample and change colour if certain substances are present. Different types of stick may test for one or more substances, which may include:

  • Blood
  • Protein
  • Glucose
  • Ketones
  • Leucocytes
  • Nitrites.

This test is widely available, inexpensive and easy to use, and so is commonly done, although it is not always 100 per cent reliable.

Blood

The presence of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. in the urine is described as haematuria. When it is visible to the naked eye it is referred to as macroscopic haematuria. Urine dipsticks are valuable in testing for smaller quantities of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. not visible to the naked eye, known as microscopic haematuria.

Causes of haematuria include disorders of the urinary tract, for example renal infections or stones, benign prostatic hyperplasiaEnlargement of the prostate, which may cause difficulty in passing urine., cancerAbnormal, uncontrolled cell division resulting in a malignant tumour that may invade surrounding tissues or spread to distant parts of the body., or simply trauma.

Haematuria may also be caused by more general disorders, for example, conditions that prevent the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. from clotting properly, such as haemophiliaA hereditary disorder that causes very slow clotting of the blood, due to deficiency of a coagulation factor (either Factor VIII or Factor IX). . Taking certain medications can also prevent the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. from clotting properly.

If a dipstick test is positive for bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. in the urine, further investigations will be needed to discover the cause.

Protein

It is normal for small amounts of protein to be excreted in the urine, and increased levels sometimes occur following exercise or fever or during pregnancy. The presence of high levels of protein in the urine is termed proteinuria.

It may be a sign of various forms of kidney disease. Other possible causes include urinary tract infectionInvasion by organisms that may be harmful, for example bacteria or parasites., fever, hypertensionHigh blood pressure. (high bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. pressure) and diabetes mellitusDisordered energy metabolism and high levels of glucose in the blood owing to a lack of insulin, or poor response of the body to insulin..

Further tests will be needed to determine the cause if protein is found in the urine on repeat testing, or if other symptoms are present.

Glucose

The most well-known cause of glucoseA simple sugar that is an important source of energy in the body. in the urine is diabetes mellitusDisordered energy metabolism and high levels of glucose in the blood owing to a lack of insulin, or poor response of the body to insulin.. However, glucoseA simple sugar that is an important source of energy in the body. may also be present in the urine in pregnancy, and in conditions such as chronicA disease of long duration generally involving slow changes. renal failure and infectionInvasion by organisms that may be harmful, for example bacteria or parasites..

Other

Ketones are a product of body fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. metabolismThe chemical reactions necessary to sustain life.. They are not normally present in the urine, but may be seen during pregnancy or following a period of starvation, or in uncontrolled diabetes.

Nitrites in the urine strongly suggest a bacterial infectionInvasion by organisms that may be harmful, for example bacteria or parasites..

The urine may also be tested for pH, a measure of the acidity or alkalinity of the urine. This may be affected by urinary tract infections and stones, or by diet, fever, medication and various other conditions.

Urine microscopy

Urine microscopy involves examining a drop of the urine under a microscope, looking for cells, bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell., crystals and casts.

Cells

Higher levels of white bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells, also known as leucocytes, may be found in the urine during infectionInvasion by organisms that may be harmful, for example bacteria or parasites. of the bladderThe organ that stores urine. or urethra The tube that carries urine from the bladder, and in men also carries semen during ejaculation.(cystitis and urethritis, respectively). They may also be present due to renal stones, among other conditions. Red bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells will be present when there is bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. in the urine ( haematuria).

Bacteria

The presence of bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell. in the urine immediately suggests urinary tract infectionInvasion by organisms that may be harmful, for example bacteria or parasites., unless the sample has been contaminated, for example, by bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell. from the skin. The next step is to send the urine for cultureThe growth within a laboratory of microbes, organisms too small to be seen with the naked eye..

Other

Urinary crystals may be found in old urine samples; if found in a fresh sample, they may suggest a higher risk of urinary stone formation.

Urinary casts are cylindrical bodies that are formed within the kidney in some types of kidney disease or infectionInvasion by organisms that may be harmful, for example bacteria or parasites., which then get flushed down into the urine. They may be composed of protein, cells, fats, pigments or crystals. The type of cast can help your doctor to assess the likely cause, but further tests may be necessary.

Urine culture

Urine cultureThe growth within a laboratory of microbes, organisms too small to be seen with the naked eye. is sometimes performed to identify which bacteriaA group of organisms too small to be seen with the naked eye, which are usually made up of just a single cell. may be causing symptoms of urinary tract infectionInvasion by organisms that may be harmful, for example bacteria or parasites., and to determine which antibioticsMedication to treat infections caused by microbes (organisms that can't be seen with the naked eye), such as bacteria. are most likely to treat the infectionInvasion by organisms that may be harmful, for example bacteria or parasites. successfully.

24-hour urine collection

Sometimes your doctor needs a more accurate measure of the quantity of various substances appearing in your urine, compared with normal ranges, and will ask you to undertake a 24-hour urine collection. This is most often performed to assess kidney disease or possible kidney involvement in diabetes.

You will be given a large container and asked to collect all the urine you produce over exactly 24 hours, usually beginning the second time that you urinate in the morning and going through to exactly the same time on the following morning.

The 24-hour urine sample may be tested to assess levels of sodium, potassium, hormones, protein or other substances, but is most often used to measure the amount of creatinineA product of the breakdown of creatine in muscle (creatine itself is fromed from the breakdown of protein)., which is a product of muscleTissue made up of cells that can contract to bring about movement. metabolismThe chemical reactions necessary to sustain life.. In this case, you will be asked to give a bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. sample at the same time to enable calculation of creatinineA product of the breakdown of creatine in muscle (creatine itself is fromed from the breakdown of protein). clearance, which measures the rate at which this chemical is cleared from the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid..

The results may be used to estimate the glomerular filtration rate, which gives information about how efficiently the kidneys are working.