Ever wonder what happens to your blood sample once it’s been collected? It’s sent “to the lab” for analysis, but what does that involve? This article will take you on a behind-the-scenes laboratory tour as a blood sample is processed.

In the laboratory, trained laboratorians use various methods to analyze your sample as determined by what types of tests you need performed. The Medical Laboratory Professionals: Who’s Who in the Lab article introduces you to these lab personnel.

For every test, there is an appropriate sample that provides the best information for that test. To learn about other types of body samples besides blood and throat swabs that can be collected for analysis, see the article Collecting Samples for Testing.

The Steps

Collecting blood

Blood draw

Depending on the facility where you have your blood drawn, a doctor, nurse, phlebotomist or other 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.

When multiple tests are ordered, more than one tube of blood may be collected, and there is a specific order in which different collection tubes with special preservatives must be drawn.

Labeling the blood sample

Blood samples with barcoded labels

Once the blood is drawn, the tube is labeled. In many labs, the label may be pre-printed with the patient’s name and unique patient identification number, or a barcoded label carrying this information is used. It is essential that the person drawing the sample label the tube properly before leaving your side.


Reading a blood sample barcode

After the sample has been collected and labeled, it is transported to the lab to be logged in to the laboratory information system. Depending on the test needed and where you have the sample drawn, your blood may be simply transported to a hospital or local lab where the analysis is performed or sent to a reference 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 analyzed for the appropriate tests and the results are matched to your name. Usually, a written or electronic requisition form listing not only your information but also your health practitioner’s name and location is sent with the sample so the results can be sent to the appropriate person.


Processing blood samples

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 blood cells by rapidly spinning the sample 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 the need for processing.

Testing (automated)

Automated lab instruments

In many cases, an automated instrument analyzes the blood sample. In some instances, the tube of blood is placed directly onto the instrument, while in other cases, a portion of the sample is first placed into a testing tube before it is placed into the instrument. Some state-of-the-art analyzers are capable of running several batches of samples — generating numerous test results per hour. In general, chemistry analyzers use samples of serum and/or plasma, and hematology and coagulation analyzers use whole blood that has not been separated into its components.


Lab professional reports results

As results are generated by the automated instrument, the lab professional evaluates them along with quality control measures to ensure that the instrument is working properly before reporting the results.

With the latest technology in analyzers comes the ability to generate the results electronically and graphically. In most cases, the results will be sent electronically to the health practitioner. If the results indicate that the patient may be very ill, the laboratory personnel will alert the healthcare provider by directly calling them with the results and will follow up by sending a printed or electronic report.

The length of time between the drawing of the blood and when the healthcare provider receives results varies depending on the test, ranging from several minutes to as much as several days. Urgency, geographic distances, processing schedules, complexity of the test, and other factors contribute to the length of time required before results are available to you and your healthcare provider.

Ask a Laboratory Scientist

Ask A Laboratory Scientist

This form enables patients to ask specific questions about lab tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. Please allow 2-3 business days for an email response from one of the volunteers on the Consumer Information Response Team.

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