Laboratory Testing

WHY DO YOU NEED A LABORATORY TEST?

Your physician will order laboratory tests in order to obtain information which cannot be learned through your history and physical examination.  This information will assist in the determination of your overall health, in the diagnosis of a disease and in the establishment of appropriate treatment.  There are many reasons for laboratory tests, all of which will provide valuable information to your doctor.

WHAT CAN BE TESTED?

Your body is made up of many different types of cells and fluids.  Almost all of these cells and fluids may be tested, though the most common specimens are blood and urine.  Materials such as sweat, spinal fluid, joint fluid, sputum, hair, feces, bone marrow, tissues and body scrapings are also analyzed.

WHO WILL PERFORM YOUR TESTS?

The clinical laboratory staff is a team of skilled professionals with education in a variety of scientific areas.  The majority of laboratory testing is performed by Medical Technologists (Clinical Laboratory Scientists) with four years of education and Medical (Clinical) Laboratory Technicians with two years of education.  Other individuals involved in clinical laboratory practice include physicians (pathologists), Ph.D. scientists (chemists, microbiologists), laboratory assistants and phlebotomists.

WHAT DO YOU NEED TO KNOW BEFORE THE TEST?

Depending upon the specific tests your doctor has ordered, you may be told not to eat for several hours before coming to the laboratory or to eat certain foods.  Other tests may require you to increase or decrease the amount you drink for 10 or 12 hours ahead of time.  You may be asked not to smoke before the tests.  When you are told by your doctor that he is ordering tests, always ask for special instructions or consult the Medical Technologist at the laboratory to learn of any special preparations which are needed.

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HOW ARE SPECIMENS COLLECTED?

For blood tests, two methods are used to obtain samples.  Your finger may be pricked for a small amount in a tube or a smear on a glass slide.  More commonly, a vein on the inner side of your arm will be selected for a venipuncture.  The laboratory professional will instruct you on the proper collection of urine samples, feces, sputum, semen or other materials which you can collect even at home.

                                                            

WHEN WILL THE DOCTOR HAVE YOUR TEST RESULTS?

Most laboratory procedures can be completed in a few hours.  This means that the doctor will have your results on the same day as the test if you are a patient in the hospital or within 2-3 days if you are an outpatient.  Some procedures, however, require several days to complete, which means that sometimes the physician will not have the results for a week.

WHAT TESTS MIGHT YOU EXPECT TO BE ORDERED?

There are over 1000 possible laboratory tests, with around 500 performed in most institutions.  The most common (the most frequently requested tests) are listed here for your information.

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White Blood Count (WBC) - the number of white blood cells to evaluate infection
 
Differential Count - the proportions of the different types of white blood cells varies in infection, allergies, etc.

Platelet Count - the count of the number of these cells which participate in blood clotting

Coagulation (clotting) studies - bleeding time, prothrombin time and other tests determine the clotting process in the blood

Hemoglobin - a measure of the oxygen-carrying capacity of the blood

                                                            

Chemistry

Sugar (glucose) - the amount of sugar in the blood is a measurement for diabetes mellitus

Electrolytes (sodium, potassium, chloride and carbon dioxide) - these substances maintain fluid and blood pressure balance and are essential for the function of most body systems

Enzymes (CK, LD, AST, ALT) - help to diagnose heart and liver diseases

Cholesterol - high amounts are associated with heart and blood vessel diseases

Urea Nitrogen - test for kidney function

Uric Acid - may indicate gout                                   
                                                     

Microbiology Culture - growth of bacteria for the purpose of identification   
                                                           

Smear/Stain - preliminary evaluation of infection
 
Sensitivity test - testing bacteria with antibiotics to determine which drug is most effective

Urinalysis

Many individual tests make up the urinalysis, such as glucose, blood, bacteria.  The physician gains information about the kidneys, liver and other body processes from these tests.

Cytology

Pap smear - microscopic examination of cells to determine abnormal conditions or malignancy

Sputum - microscopic evaluation for malignancy or other disorders such as asbestosis

                                                                  

Histology

Biopsy - the removal of a small section of tissue to be studied.  The type of cells and their chemical reactions are evaluated. 
                                                                    

Immunology

AIDS test - positive when a person has the AIDS virus
Pregnancy test - to confirm pregnancy
Rubella test - for measles

lmmunohematology (Blood Bank)

Blood type and Rh - to identify a person's blood type which can be O, A, B or AB and Rh which can be either positive or negative

Cross match (compatibility test) - to determine if a unit of blood may be used for a transfusion for a particular patient

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WHAT ABOUT ALL THOSE HOME TESTING KITS AVAILABLE IN DRUG STORES?

In today's health care environment, there is a movement toward involving the patient more in their own health, and making all of us educated consumers of healthcare. Such patient involvement can include just taking better care of ourselves through diet and exercise. It also includes monitoring risk factors for certain diseases. Some of the tests which have traditionally been done only in a clinical laboratory have been miniaturized into home testing kit versions, which allow you to monitor certain important blood chemicals conveniently at home, on your own schedule. Currently available are kits for glucose (blood sugar), pregnancy, cholesterol, ovulation (when you're trying to become pregnant), occult blood (bleeding in the intestines), and testing for HIV (the cause of AIDS). Each of these kits is a marvel of technology, but will only give reliable results if the steps are performed exactly as required in the kit directions.

HAVE A QUESTION ABOUT A LABORATORY TEST?

If you have any questions about doing a test, or interpreting the results, contact the webmaster, and a certified clinical laboratory scientist from Pennsylvania will gladly help you!
 

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