Lab tests on urine
Your urine may contain several substances which may be of interest to your doctor or midwife. Your urine is the product of your “urinary tract”. Another term, renal, refers more specifically to the kidneys themselves. Your urinary tract consists of the urethra, bladder and kidneys (2 kidneys, right and left). The kidneys filter impurities from your blood. Your kidneys are extremely delicate organs. If they are damaged, these impurities can build up in your blood, and substances which should stay in your blood can leak out into the urine. Your kidneys also secrete substances that are partly responsible for control of your blood pressure.
Some diseases which effect the urinary tract are caused by infection from bacteria. Bacteria can reach the kidneys through the blood (which is rare) or ascend from the lower urinary tract (which is much more common). But not all urinary tract problems are caused by infection. The kidneys are sensitive organs and can be damaged by other disease processes.
Pregnancy places a demand on the urinary tract which most women adapt to easily. However, because of these added stressors, it is important that any problems be recognized early. Damage to the kidneys is often permanent. And, acute kidney disease may cause the uterus to begin to contract prematurely.
human Chorionic Gonadotropin (hCG)
One substance that is normally allowed to leak out through the urinary tract is hCG. hCG is a hormone produced by the cells that surround the developing placenta of an embryo. hCG leaks into both the blood and urine of the mother. hCG is the substance which is the basis of pregnancy tests since it is usually only produced during pregnancy.
A rare condition, called hydatidiform mole, may cause abnormally high levels of hCG to be released into the mother’s blood stream. Often referred to as a “molar pregnancy”, this condition arises when the cells destined to become the placenta begin to grow eradically; much like cancer. In fact, one of the lingering problems in a woman with a molar pregnancy is development of a rare cancer of the uterus. After pregnancy, these women usually need periodic measurements of hCG to assure that they do not develop this cancer.
hCG is partially responsible for the nause (and vomiting) which some women experience in early pregnancy. Women with molar pregnancies usually are more nauseated because of the higher levels of hCG. This can also happen with multiple gestation pregnancies, in which there is often a larger placenta producing more hCG.
At most prenatal visits, your midwife or doctor will check a sample of your urine for protein and glucose. Glucosuria (glucose in the urine) is often discounted as a normal finding in an otherwise healthy pregnancy. However, if your blood glucose is abnormally high, glucose in the urine may be a related finding. On the other hand, significant amounts of protein (more than a “trace”) should always be investigated more closely. If you have “one-plus” (“1+”) or more protein in your urine, your clinician may order additional urine or blood tests, or schedule your next prenatal visit sooner (see Hypertension in Pregnancy).
If a pregnant woman has a significant amount of protein in the urine, depending upon many other factors, the doctor or midwife may want to do a “24-hour urine”. Armed with a empty-milk jug and a collection “hat”, you save an entire 24-hour’s worth of urine……stored in your refrigerator, no less. By measuring the total amount of urine, protein and creatinine, your clinician will get a good picture of your “renal status” from a 24-hour urine. A 24-hour urine is a common test in women with pre-eclampsia whose baby is still quite premature. In this case it’s important to know the status of the mother’s kidneys and disease progression to determine how long to wait for the baby to mature.
A “urinalysis” or “UA” is a test which may use either chemical or microscopic techniques (or both) to determine the contents of your urine. The UA can detect blood cells (both red and white), bacteria, and the chemical components of urine such as glucose, protein, ketones, and nitrites (Glossary).
A “urine culture” is a test to determine if, how much, and what kinds of bacteria may be in your urine. The urine is “cultured” so that any bacteria in the urine will reproduce in numbers large enough to be identified. A small amount of urine is placed in a lab dish with food for bacteria (the “medium”) and heated to keep it warm (like your body). If there is bacteria in your urine, it will grow in the medium. If it does grow, the bacteria is identified and subjected to different types of antibiotics to see what might kill it. The entire test is called a “culture and sensitivity” test (or “C&S”). It may take 24-72 hours to get the final results of a C&S. If you have the symptoms of a urinary tract infection, your clinician may not wait for the results, but rather start treatment (usually antibiotics) to keep a possible infection from “ascending” to the kidneys.