|Learn About Lab Tests
Your doctor may order a lab test for one or more of the following reasons.
To confirm a suspected diagnosis
e.g. Glucose to confirm diabetes mellitus.
To exclude a diagnosis.
e.g. A negative urine culture rules out bladder and kidney bacterial infection.
To check that treatment is working effectively.
e.g. Increasing hemoglobin level shows that anemia is responding to treatment with iron pills.
To monitor prescription drug levels.
e.g. Digoxin level. To check that the amount of digoxin (a heart drug) is at the appropriate level to work effectively.
To screen for a treatable condition.
e.g. Pap Smear in women to detect early or pre-cancer of the cervix.
What kinds of lab tests are there?
Lab tests are carried out to measure or detect substances in a person's body. There are several types of test - Hematology, Immunology, Chemistry, Microbiology and the emerging area of Molecular Diagnostics. There are a number of other tests that are "miscellaneous".
Most tests are analyzed on sophisticated instruments under computer control. Our labs use "state-of-the-art" robotics and conveyor systems to move samples and keep track of our work. Indeed, our staff has been involved in the development of this system that is manufactured by MDS AutoLab, a division MDS. We also have highly sophisticated computerized Quality Control Systems for insuring the most accurate results possible.
Hematology is the study of the blood system. There are three kinds of cell in the blood stream: red cells, white cells, and platelets.
Red blood cells (RBC) contain the hemoglobin molecules that give blood its red color. They are responsible for carrying oxygen from the lungs to all the parts of the body. White blood cells (WBC) are much less numerous than red cells. They are vital in helping the body fight infection. There are several different kinds of WBC.
Platelets, tiny fragments of cells, help stop bleeding by forming “plugs” in the blood vessels.
The standard Hematology test is called a Hematology Profile. In this test a sample of the patient’s blood is put into a large machine - an automated analyzer. This measures:
- the total amount of hemoglobin,
- the number of red cells,
- the total number of white cells (WBCs),
- the number of the various types of white cells, and
- the number of platelets,
If an abnormality is found in the profile, it may be necessary to examine the blood with a microscope.
This is a picture of a blood smear as seen by a microscope. The red cells are the smaller, more numerous round objects. There are two white cells in the middle (they are blue because they have been stained).
When the red cells are low and/or when the hemoglobin content is low then anemia is present. There are many causes of anemia but lack of iron is a common one. A low WBC count is often the result of a viral infection. The WBC count goes up in bacterial infections such as Strep throat or urinary tract infection. Leukemia is a cancer of the white blood cells. Low platelet counts are found in a variety of disorders. If the platelet count is very low, the patient is at risk of bleeding.
Coagulation Tests: The Hematology discipline also studies how efficiently blood clots. Some people have a bleeding tendency (for example Hemophiliacs) which can be studied with these tests. Some people must take drugs to "thin" their blood and prevent it from clotting too quickly. The PT (Prothrombin Time) or INR (International Normalized Ratio) is used to monitor such drugs.
Other hematology investigations include: Mono Tests to help diagnose the presence of Infectious Mononucleosis, or investigations of the molecular structure of the Hemoglobin molecule in order to detect the presence of abnormal hemoglobins.
Immunology tests assess the body’s immune system. When the immune system “over-reacts”, an autoimmune disease (for example, Lupus Erythematosus) is caused wherein the body regards its own tissue as a “foreign substance” and begins to inflict damage on itself. When the immune system “under-reacts” the patient is unable to ward off infections in the normal fashion. There are a variety of tests that help clarify disorders of the immune system.
The Microbiology lab helps to determine what is causing an infection and how best to treat it. Testing employs swabs, blood, urine, or feces. Swabs are sticks with cotton wrapped around one end. These can be placed in an infected area (like a sore throat or a wound) in order to “pick up” some of the bacteria that are causing the infection. Swabs or other materials are smeared on the surface of a small plate of agar (a gelatin-like material) and placed overnight in an incubator that is maintained at body temperature. After incubating, the plates are removed and examined for the presence of bacterial growth. Using a microscope, special stains, and chemical tests, technologists can determine the type of bacteria that is present.
The picture shows a plate covered with growing bacteria colonies. On the middle of the plate are two pieces of confetti-like paper that have been impregnated with antibiotics. These antibiotics show their effect on the bacteria by creating a zone of “no growth” around them.
In addition, the lab can determine which antibiotics will inhibit or kill the bacteria. The presence of Parasites in feces can also be detected in this part of the lab.
There are many different kinds of chemistry test.
Routine Automated Chemistry: Most of the common chemistry tests are carried out on large automated analyzers. Some examples of "routine" tests are:
Glucose is measured for the diagnosis and monitoring of Diabetes Mellitus.
BUN and Creatinine are tests of kidney function.
Calcium and Phosphorus are tests used to evaluate Calcium physiology. These tests do not reveal any information about osteoporosis but may assist in the diagnosis of the cause.
Sodium and Potassium are salt balance tests. They are important in people with kidney disease and in people taking diuretics.
Liver function tests include Bilirubin, Alkaline Phosphatase, Aspartate Aminotransferase, and Gamma Glutamyl Transpeptidase.
Total Protein and Albumin provide information about liver function, kidney disease, infection, nutrition, and certain disorders of the antibody producing cells.
Drug testing is of two types.
Drug screening is used to detect illicit drug administration. These tests are carried out on persons receiving drug treatment with Methadone, on those who have "overdosed", and for legal purposes.
Therapeutic Drug Monitoring (TDM) is carried out to help control the dose of prescription drugs.
These tests evaluate various hormones.
Thyroid Function Tests (TSH and Free T4) detect disorders of the thyroid gland and assist with treating thyroid disease.
Testosterone: The "male" hormone. A clinical problem will occur if it is too low in men or when it is elevated in women.
LH and FSH are tests of the hormones that control the menstrual cycle in women and the production of testosterone and sperm in men.
Chorionic Gonadotropin: A hormone produced in pregnancy and the material detected in pregnancy tests.
This is a common evaluation consisting of a series of chemical tests. These are conducted using a chemically coated plastic strip (dipstick) which is soaked in the sample and then "read" by visual appearance or using a machine. The tests help to detect diabetes, liver disease, diseases of the kidney and bladder and some blood disorders and infections. The urine may also be examined under a microscope to confirm findings. The picture shown here is a microscopic view of crystals that have formed in urine.
Molecular Diagnostics is a rapidly expanding field. It relies on DNA testing and the ability to detect the presence of specific genes. Every month there are new discoveries in this area allowing us to detect and/or diagnose microorganisms, genetic disease, disease risk factors, and sub-types of disease. One example of this type of testing is Paternity Testing.