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.
Dentro do laboratório: Siga essa amostra.
Ao acionar um interruptor, as luzes se acendem. Ao abrir uma torneira, você pode lavar as mãos. Deixe alguém espetá-lo com uma agulha - ou dê algo de seu corpo a alguém - e obtenha informações sobre sua saúde.
É assim que os testes de laboratório têm sido vistos até recentemente. Exceto pelo seu contato com o profissional que colhe a sua amostra, é raro conseguir saber quantas pessoas estão envolvidas na geração de um resultado de teste de laboratório. Você também não encontra muitas oportunidades de aprender o que acontece após a amostra desaparecer de sua vista.
Como os laboratórios assumem um papel cada vez mais importante na área da saúde, a compreensão do que ocorre nos bastidores é quase tão importante quanto saber o que pode ser aprendido com os resultados dos testes. Os artigos abaixo foram elaborados para explicar um pouco mais sobre o laboratório e como ele funciona.
Collecting the Culture
Labeling the Culture
Documenting the Culture
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.
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.
In most cases, an instrument, appropriately called a blood analyzer, analyzes the blood sample. In this picture, the tube of blood is being placed directly into the machine. This particular state-of-the-art analyzer is capable of running batches of samples -- up to 120 samples per hour. In general, chemistry analyzers use serum and/or plasma, and hematology and coagulation analyzers use blood that contains an anticoagulant to prevent clotting.
With the latest technology in analyzers comes the ability to generate the results electronically and graphically. In this case, the results will be sent via email electronically to the doctor. In many situations, results are printed and then faxed to the doctor. If the results indicate the patient may be very ill, the laboratory will call the doctor with the results.
The length of time between the drawing of the blood and when the doctor gets the results can vary greatly, from as little as a few minutes to as much as several weeks. Urgency, geographic distances, processing schedules, complexity of the test, and other factors explain why it may sometimes take so long to learn your results.
Collecting a Throat Culture
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.