Dentro do laboratório: Siga essa amostra.

As a patient, the lab test that has been ordered by your doctor may require that you have your blood drawn from a vein in the arm (venipuncture) or a fingerstick. It may also consist of, for example, a throat culture (taken by a swab rubbed against the back of your throat), a urine sample, or another sample of body fluid or even tissue (biopsy). Once the sample is obtained, you are finished with your part of the "lab test;" however, the real test happens in the laboratory where trained laboratorians use various methods to analyze the sample. Let's look at a couple of examples: a blood sample and a throat culture.

Collecting

Depending on the facility where you have your blood drawn, a doctor, nurse, laboratorian, or another medical professional will draw your blood. In this picture, a phlebotomist has inserted a needle into a vein on the outer portion of the arm near the elbow.

Labeling

Once the blood is drawn, the tube is labeled. In many labs, the label will be pre-printed with the patient’s name, identification number, and number assigned to that specimen. It is essential to label the tube properly before leaving the patient’s side.

Documenting

After the sample has been collected and labeled, it is transported to the lab to be logged in. Depending on the test needed and where you have the sample drawn, your blood may be simply transported to the lab where the analysis is perfomed or flown across country to a lab that specializes in a particular blood analysis.

Once the specimen arrives in the lab, however near or far away, your blood sample will be logged into the laboratory's tracking system. The tube label contains all the information necessary to ensure that the sample is run through the appropriate tests and the eventual results are matched to your name. Usually, a form listing not only your information, but also your doctor’s name and address is sent with the sample so the results can be sent back to the doctor.

Processing

Depending upon the tests that have been ordered, your blood sample may be processed before it is analyzed. Most routine laboratory tests are performed on either plasma or serum. Plasma is the liquid portion of blood. It is separated from the cellular portion of blood by rapidly spinning the specimen in a centrifuge for several minutes. The plasma, which has a light yellow color, appears at the top of the tube, while the blood cells are at the bottom.

Serum is plasma that has been allowed to clot. It is prepared in the same way as plasma - however, the blood is collected into a tube with no anticoagulant. While spinning in the centrifuge, the clot moves with the cells to the bottom of the blood collection tube, leaving the serum on top.

If the test requires whole blood (e.g., a complete blood count), the sample can be analyzed directly without further processing.

Collecting

A culture is a test that is often used to detect infections. It involves collecting a sample from the body site where the infection is suspected to be and introducing the sample into solid or liquid nutrient media (e.g., agar, gelatin) in order to grow any microorganisms like bacteria or fungi that may be present. Cultures can be performed on a variety of body samples, including blood, urine, stool, sputum, and pus from a wound. Collection methods therefore depend on where the suspected infection is located and the type of sample being taken. The example pictured here is a throat culture where a swab is rubbed over the back of the throat to collect a sample for culture.