Lab tests are performed to check the health of a patient. Blood, urine and other substances are performed to diagnose, treat or prevent the onset of conditions and diseases.
1 AnswerDr. Jack Merendino, MD , Endocrinology Diabetes & Metabolism, answeredThere are times that the hemoglobin A1c result does not accurately reflect a person’s average blood glucose readings. Hemoglobin A1c is created when glucose in the blood comes into contact with the hemoglobin inside a red blood cell. When a red blood cell is first created in the bone marrow, there is no hemoglobin A1c. As the cell circulates in the bloodstream over its life expectancy of about 4 months, hemoglobin A1c accumulates to a greater and greater degree. The oldest cells -- the ones that are closest to the end of their life cycle -- have the highest amount of hemoglobin A1c. Therefore, the amount of hemoglobin A1c in the blood varies depending not only on how much glucose there is in the system, but also on the rate of production of red blood cells, the rate of destruction of those cells, the average life span of a red blood cell, and factors that may affect the rate at which glucose attaches to the hemoglobin.
The hemoglobin A1c usually underestimates the average glucose in the blood in settings in which red blood cells do not survive as long as they should in the blood. A simple example might be if someone has major blood loss, such as following an accident or surgery. Assume that the person has lost a fair amount of blood, but not enough to need a transfusion. In this case the bone marrow revs up to replace the lost blood at a faster rate than normal, and a higher percentage of the red cells are relatively young, with little hemoglobin A1c in them. This results in a lower hemoglobin A1c than would be expected for the glucose level.
The opposite situation occurs in people with sickle cell disease. People with sickle disease have an abnormal form of hemoglobin in their blood -- hemoglobin S -- instead of the normal hemoglobin A. Hemoglobin S causes the red blood cells to assume a sickle or crescent shape in some settings. But hemoglobin S has another characteristic, which is that it combines with glucose to form hemoglobin A1c at a faster rate than normal hemoglobin A. Therefore, people with sickle disease will have a hemoglobin A1c that overestimates their average glucose levels and will make their diabetes look more poorly controlled than it actually is. This is true also of people with sickle trait, though to a lesser degree because they have lower levels of hemoglobin S.
1 AnswerpH is a scale from 0 to 14 that measures how acidic or basic a substance is. A pH less than seven is acidic. A pH greater than 7 is basic. Seven on the pH scale is neutral.
For example, lemonade a drink high in citric acid, has a pH of about 2.2 to 3. Ammonia is basic and has a pH of about 11 to 12. Pure water has a neutral pH of 7.
1 AnswerA urine pregnancy test is a chemical test that detects the presence of a hormone called human chorionic gonadotropic or HCG, which is produced in a woman's body during pregnancy. Many urine pregnancy tests are at-home tests that require a woman to urinate on a test strip or to collect urine in a sterile sample cup and either dip a test strip into the urine or place a few drops of urine from the cup onto a test stick.
Most urine pregnancy tests suggest waiting at least two minutes before reading the result. A urine pregnancy test is positive if HCG is detected in the urine. Depending on the test, a positive result may cause a line to appear or a plus sign or other change in the test strip.
Urine pregnancy tests have about a 99 percent accuracy rate when used according to directions. They may be able to detect a pregnancy as early as 10 days after conception, but most tests recommend taking the test after a missed menstrual period. Using your first urine in the morning is also sometimes recommended as HCG concentration may be higher at that time.
If you have a positive result on a urine pregnancy test, call your doctor, who may want to follow up with a pregnancy test on your blood, which can detect not only whether HCG is present but how much, which can give clues to the health of your pregnancy.
1 AnswerA urine culture is a laboratory test that examines a urine sample for bacteria or other germs. Urine cultures are performed commonly to determine if someone has a urinary tract infection.
Common symptoms of a urinary tract infection include:
- frequently feeling that you need to urinate, but not producing much urine when you do urinate
- feeling pain or burning when you urinate
- abdominal pain
If bacteria is present in your urine in high amounts you have a positive test which means you have a urinary tract infection. Your doctor may treat you with medication, including antibiotics. If your test comes back negative but your symptoms persist, your doctor may want to repeat the urine culture in a day or two.
1 AnswerA toxoplasmosis test is a laboratory blood test to detect a current or past infection with a parasite called toxoplasma gondii. If you are infected with this parasite, your body's immune system produces antibodies to fight it. The toxoplasmosis test looks for and measures the level of those antibodies. Toxoplasma gondii is especially dangerous in people who have weak or compromised immune systems (such as people who have AIDS) or in pregnant women. If a pregnant woman develops antibodies during pregnancy detected by the toxoplasmosis test, the doctor may order a test on the amniotic fluid to determine the risk to her developing baby. The toxoplasma gondii parasite is transmitted from raw or undercooked meat, by consuming contaminated food or water, or by handling cat litter (since cat feces is a carrier of the parasite).
1 AnswerA toxicology screen is a group of laboratory tests that are performed to detect drug abuse (including alcoholism), to monitor someone who has a drug abuse problem, or to evaluate drug intoxication, poisoning or overdose. Toxicology screens typically analyze blood or urine, but may also involve the examination of stomach contents obtained by suctioning out the contents through a process called gastric lavage or from vomiting.
Toxicology screens may be ordered as part of a screening process for a new job, randomly as part of workplace or athletic program drug testing. It may also be done in an emergency room for medical and/or legal purposes to determine the drugs that someone might have ingested.
For accuracy, toxicology screens typically need to be done within a certain amount of time after a drug is ingested. This time period varies, depending upon the drug in question. For example, screening for alcohol usually needs to be done three to ten hours after ingestion; screening for cocaine can be done as much as four days after ingestion.
1 AnswerA throat culture test is a laboratory test that is performed to identify the cause of a sore throat, most commonly to see if someone has strep throat. Before ordering a throat culture test, your doctor will first rub a sterile cotton swab along the back of your throat near your tonsils. That cotton swab will then be sent to a laboratory where it will be put on a special plate to allow any bacteria on the swab to grow. The laboratory technician can then examine the swab for signs of bacteria, and usually can provide results within one to three days. A positive throat culture for strep throat means the swab was found to contain group A streptococci, the bacteria that causes strep throat. (Less commonly, sore throats may be caused by group C or group G streptococci.) Your doctor may prescribe antibiotics to help clear up the infection. A negative throat culture means you do not have strep throat, but more likely a viral infection that is causing your sore throat that will likely resolve on its own.
1 AnswerA stool analysis (or stool test or stool culture) is a laboratory examination of a sample of feces, or "stool," usually to determine the cause of a problem in the gastrointestinal tract. In a stool analysis, a stool sample is collected in a sterile container. Doctors may order a stool analysis to:
- Have the stool checked for bacteria and/or parasites. This can be done by putting a small amount of the stool on a slide and viewing it under a microscope. In some cases a special stain can be used on the slide to make the organisms easier to see.
- Check the stool for blood, which might indicate bleeding in the gastrointestinal tract or infectious diarrhea.
- Examine the stool for signs of malabsorption problems. For example, fat in the stool may be a sign of certain digestive disorders.
1 AnswerA progesterone test is a laboratory test to measure the amount of progesterone (a hormone made by a woman's ovaries) in the blood. There are several possible reasons a woman may have her progesterone level tested.
- A progesterone test is often part of an infertility workup. A progesterone test can help a doctor determine if and when a woman has ovulated, or if ovulation-inducing medications are working.
- A progesterone test may be ordered early in a pregnancy if the doctor suspects the pregnancy is failing or is ectopic (implanted in a fallopian tube rather than in the uterus).
- Progesterone tests can help a doctor determine the cause of repeated miscarriages in a woman who is experiencing them.
- Progesterone tests are a way to evaluate the placenta and the health of a developing fetus during pregnancy, especially a high-risk pregnancy.
- Progesterone tests can be a way to monitor the effectiveness of progesterone therapy during pregnancy, if a woman is receiving progesterone injections to help support the pregnancy.
- In a non-pregnant woman, a progesterone test may be ordered along with other tests to try to determine the cause of abnormal bleeding from the uterus. High progesterone levels may be an indicator of some forms of cancer, or a problem with the adrenal glands.