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Urine tests

Urine tests


Pregnant women can have their urine tested for a variety of things. They can be done by providing a urine sample in jar or a sterile sample to look for an infection, or by passing urine directly onto a reagent strip of coloured litmus paper (called a dipstick). How, when and why your urine may be tested varies between caregivers and hospitals. It may be a standard routine procedure done at every pregnancy visit or something that is only done for some women to investigate possible health concerns.

Routine urine testing at every pregnancy visit is becoming less common in Australia, mainly because it has been found to have little benefit for either the woman or her baby, unless other physical signs are present (such as higher blood pressure). However, some caregivers continue to routinely test every woman's urine at every pregnancy visit. If this is the case, you may be asked to bring a sample in a container to each visit, or to simply test your own urine in the toilet when you arrive for your check-up.

The following is a general guide as to why your urine may be tested and what your caregiver is looking for.

Pregnancy tests

Urine infection

Protein

Glucose

Ketones

Pregnancy tests

The first urine test most women have is a pregnancy test. Modern urine pregnancy tests rely on an immunoassay testing technique to detect the presence of human gonadotrophin hormone or HCG, which changes the colour of a line or dot marker. If a pregnancy test is used as directed and done when the next period is overdue, they can be up to 97% accurate. However, if the test is done incorrectly, too early and/or with a weak (or dilute) urine sample, they are about 75% accurate.

Urine pregnancy tests can be purchased in supermarkets and pharmacies to use at home. Similar tests may also be used by local doctors or women's health nurses during a medical check to detect a pregnancy, or as a secondary confirmation of your home pregnancy test (hpt). You can read more in pregnancy testing.

Urine infection

The urine test

About 5 to 10 % of women (pregnant and non-pregnant) have what is called asymptomatic bacteriuria. Put simply, this is a small amount of bacteria present in the bladder without the women actually having any physical signs. In non-pregnant women asymptomatic bacteriuria does not tend to cause any problems. However, during pregnancy, the hormone progesterone relaxes the walls of the bladder and ureters and the growing baby often compresses these organs, sometimes leading to urine refluxing back up into the kidneys and left pooling in the woman's bladder after urination, encouraging bacteria to multiply, sometimes leading to an infection. Pregnant women also have extra glucose present in their urine, which can feed the bacteria, encouraging a bladder infection.

About 20 to 30 % of pregnant women with asymptomatic bacteriuria can develop a urine infection later in their pregnancy, possibly leading to premature labour and birth. It is for this reason that many caregivers ask for a midstream sterile urine sample at the first pregnancy visit to send to the pathologist for testing (although this is not routine and not all caregivers do this). If bacteria are found to be present in the urine, the caregiver will probably suggest a course of antibiotics to treat it. However, some women choose to only accept antibiotics if and when they actually develop an infection later in the pregnancy. You can discuss your preferences with your caregiver.

As the pregnancy progresses, your caregiver may ask you to provide a urine sample for testing if you (or they) suspect you have a bladder infection (called cystitis or a urinary tract infection - UTI). If the infection has moved up into your kidneys it is called pyelonephritis. The physical signs of a urine infection can include:

  • Passing urine more frequently.
  • A burning or stinging sensation when urinating.
  • A constant ache in the lower belly.
  • Headache, vomiting, low blood pressure and/or a fever or chills.

A kidney infection can also cause constant backache across the middle and sides of your back, at about waist level and perhaps blood in the urine making it look pink, red or brown. In some cases the woman is not aware she has a urine infection because she does not have the typical physical signs. The infection may present as moderate, lower abdominal pain, a fever and possibly mild contractions of the uterus during middles to late pregnancy, like premature labour. In fact, an infection of the urine after 20 weeks of pregnancy can lead to premature labour and birth for up to 50% of women if left untreated.

The most common bacterium causing a urine infection is E. coli, which is present in large quantities in the bowel as well as the vaginal area, being easily transferred to the bladder. Another organism that may be present in the urine is Group B streptococci, known as GBS or Group B Strep, which may cause an infection of the baby later in the pregnancy or during labour (about a 1% chance). The presence of Group B Strep in the vagina is often tested for later in the pregnancy with a vaginal swab. You can read more in Group B strep.

The urine test.

To diagnose an infection of the urine you need to provide a mid-stream sample of urine passed into a sterilised container (also called a MSU or Microurine). Taking a sample midstream involves you passing a little bit of urine into the toilet, then passing a small amount of urine into the sterile container (this is the middle of the stream), then passing the rest of your urine into the toilet. Easier said than done! The aim is to flush any vaginal secretions away so the urine is a clean catch and not contaminated. A contaminated urine specimen usually means the test needs to be repeated.

The result of an MSU test takes about 48 to 72 hours and is usually recorded on your pregnancy records as No Growth (negative) or 'positive for' and then the name of the bacteria involved.

Protein

Protein (or albumin) is a very large molecule that floats in the blood. The kidneys act like a fine sieve filtering the blood and generally preventing protein from being passed into the urine. During pregnancy, it is normal for the kidneys to excrete small amounts of protein. However, large amounts of protein in the urine (or proteinuria) can be a physical sign of very high blood pressure during pregnancy or pre-eclampsia. This is because an abnormally high blood pressure can cause the sieve in the kidney to become somewhat impaired or damaged, allowing more protein to slip through into the urine. Proteinuria is also a physical sign of a urine infection or underlying kidney disease.

In practice, protein in the urine is tested for by using rapid urine screening tests in the form of reagent strips, known as dipsticks. They have many small, coloured squares of litmus paper on them and are designed to be soaked with urine to get a result. The urine is placed on the dipstick either by putting the dipstick into a urine sample, or by the woman passing urine over the dipstick in the toilet. If certain substances are present in the urine, such as protein, the relevant litmus square on the dipstick changes colour. In the case of protein it usually changes to a darker shade of green.

Urine testing Image 4-52 shows the reagent strips or dipsticks used to test many components of the urine, one being protein or albumin.

The results of a dipstick test show as negative, or 'a trace' or 1+, 2+, 3+ or 4+. It is normal to obtain results of a trace to 1+ during pregnancy, either because of the normal small amount of protein present in the urine or because vaginal discharge during pregnancy affects the reagent on the stick. A reading of 2+ or above is considered significant and may be of concern.

Routine testing for proteinuria at every pregnancy visit has not been shown to be effective. In recent years caregivers have moved away from doing this at every pregnancy visit, but may suggest you do the test if your blood pressure is higher than usual (if you are more than 20 weeks pregnant). The definitive test for proteinuria is a 24-hour urine collection, which means you collect all your urine over a 24 hour period in a large plastic container. Proteinuria is not considered abnormal until it exceeds 300mg in 24 hours, which may or may not be detected in random urine sample testing.

Glucose

Up until the late 1990's, testing for glucose in the urine during pregnancy (called glycosuria) was routine at every pregnancy visit to possibly indicate gestational diabetes. However, it is now recognised that glucose in the urine is a very normal physical variation during pregnancy because the kidneys function much more efficiently, allowing some glucose to pass into the urine before the woman's body is able to utilise it all for energy.

Testing urine for glucose is done in the same way as testing for protein, with reagent strips known as dipsticks. When the dipstick is soaked with urine, the glucose indicator changes colour (usually to a khaki green colour). This routine testing for glucose during pregnancy is now considered outdated, because it is not an indicator for diabetes. Diabetes can only be tested for with a glucose tolerance test.

Ketones

Ketones may be passed into the urine if a person is dehydrated and lacks sufficient carbohydrates (or glucose) in their blood stream for energy in the body. If the muscles have little or no glucose for energy to function efficiently, they start breaking down the body's fat stores for energy instead, producing ketones that can be detected in urine. In cases where ketosis is prolonged, the condition can develop into ketoacidosis, something that can occur for people who have uncontrolled diabetes .

In the past, ketones were tested for during routine pregnancy visits to see if the woman's diet was adequate (particularly for women having twins or more). However, they are now only tested for during pre-labour or labour to monitor hydration and energy reserves. This aims to preven labour contractions from weakening, slowing or stopping. Testing for ketones is done in the same way as tests for protein and glucose, with reagent strips known as dipsticks. You can read more in ketosis.

Last revised: Saturday, 10 November 2012

This article contains general information only and is not intended to replace advice from a qualified health professional.

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