A typical tour of the laboratory by a blood sample

Dr David Howdijam *

Do you ever wonder what happens to your blood sample after it has been collected? Obviously, it is sent “to the lab” for analysis, but what does that mean?

What does that entail? This article will take you on a tour as a blood sample is processed. There are various stages that it follows – collection, processing, testing, analysing, preservation and ending with it being discarded from the lab.

In the laboratory, trained personnel use different methods on various equipment to analyse your sample according to the type of tests asked for.

Also, for every test, there is an appropriate sample that provides the best information for that test.

For instance, there are tests that could be performed on both blood sample and other body fluids (e.g. blood sugar and urine sugar) but depending on what is being investigated for, an appropriate sample is chosen as prescribed by the treating doctor.

Depending on the size and type of the laboratory where the test is conducted, the path through which a blood sample goes through will vary.

The route in a small lab and large lab will be vastly different. This article will illustrate is how a blood sample will go through the various steps in a modern, large laboratory.

COLLECTION OF BLOOD SAMPLE

Depending on the facility where you have your blood drawn – whether in a doctor’s chamber, hospital or a laboratory – a nurse, phlebotomist or a laboratory technician will draw your blood. Mostly, the blood is drawn from a vein on the outer portion of the arm near the elbow.

In instances when multiple tests are asked, more than one tube of blood may be collected. There are specific sample collection tubes for different types of tests, and the trained lab personnel will collect the blood in appropriate tubes. There is also a specific order in which the different tubes with (or without) special preservatives must be drawn. The person collecting the sample logs in to the system under unique IDs assigned to him or her for better identification and traceability.

LABELLING THE SAMPLE

Once the blood is drawn from you, the tube is labelled. In many laboratories, the label may be pre-printed with the patient’s name and unique identification number, or a barcoded label is used. The barcode contains all necessary information like the patient’s details and the tests to be done. It is essential that the laboratory person drawing the sample label the tube properly before leaving your side.

TRANSPORTATION OF SAMPLES

The samples are transported to the specific lab sections, either physically or via pneumatic tubes that deliver the sample tubes to the lab directly. Once the specimen arrives in the lab, your blood sample will be received by a technician after logging into the laboratory’s tracking system commonly called Laboratory Information Systems(LIS).

The tube label contains all the information necessary to ensure that the sample is analysed for the appropriate tests and the results are matched to the patient’s name. Usually, a written or electronic requisition form listing not only patient’s information but also health history is sent with the sample so that they can beseen to the appropriate person to correlate the information.

SAMPLE PROCESSING

Depending upon the tests that have been ordered, your blood sample may be processed before it is analysed. Routine laboratory tests are performed on whole blood, plasma or serum. Plasma is the liquid portion of the blood. It is separated from the cellular portion of blood by rapidly spinning the specimen in a centrifuge for several minutes.

The speed (in rpm) and the duration of this spinning is set as per the type of the test to be done. The plasma, which is light yellow in colour, appears at the top of the tube, while the blood cells settle at the bottom. Serum is the plasma that has been allowed to clot. It is prepared in the same way as plasma.

However, here, the blood is collected in a tube without anticoaglulent. While spinning in the centrifuge, the clot moves with the cells to the bottom of the blood collection tube, leaving serum at the top.

On the other hand, there are tests like the Complete Blood Count that requires whole blood sample. If this is the case, then the whole blood is analysed directly without further processing.

TESTING

In most cases, an instrument analyses the blood samples. Modern laboratory instruments are mostly automated. These equipment have the capability to run batches of samples at one time, sometimes in hundreds of samples in an hour. In general, chemistry analysers use serum and/or plasma, and haematology and coagulation analysers use blood that contains an anticoagulant to prevent clotting.

TEST RESULTS

Today’s modern analysers come with the ability to generate the results electronically and graphically. These machines are interfaced with the LIS (unidirectional or bidirectional) and the results generated from them are entered automatically. The results are then checked for any anomalies by the technicians. These are then forwarded to the medical practitioner (Pathologist or Biochemist) for electronic authentication.

The results, after authentication are transmitted electronically via the LIS for printing or downloads.

The length of time between the drawing of blood and when the results are ready can vary greatly, from as little as a few minutes to a whole day (or even a few days). The tests are also scheduled as per their urgency. Hence, urgency, processing schedules, test schedules, complexity of tests, and other factors contribute to the length of time required before the results are made available to the patients or the health practitioner.