Blood Sample Handling and Processing

Last Updated on March 4, 2021

After taking a blood sample, the blood needs to be managed in a proper way so as to prepare it for investigations.

Blood sample handling and processing can be summarized as below.

Read more about Blood Sampling or Blood Collection Methods

Read more about Phlebotomy- Indications, Procedure, and Complications

Read more about Vacutainer ® and Their Use in Blood Sampling

Pre-centrifugation Handling

The first critical step in the lab testing process, after obtaining the sample, is the preparation of the blood sample.

Specimen integrity can be maintained by following some basic handling processes –

• The tubes should be filled up to the desired level which is usually indicated on the tubes so as to ensure a proper blood-to-additive ratio. In the case of Vacutainer ®, the tube should be filled until the vacuum is exhausted and blood flow ceases. Blood should not be forced vigorously into tubes beyond/under the indicator mark.
• The blood-filled tubes should be stored at 4-25°C (39-77°F).
• Expired tubes should not be used.
• Immediately after filling, the tubes should be inverted gently a few times. Turn the filled tube upside­ down and return it to an upright position. [see image below] This is one complete inversion.
• Proper mixing assists in the clotting process in the case of gel and barrier tubes. In the case of additive tubes, it ensures homogenous mixing of the additives and the blood.

A short summary of inverting the tubes is given below.

• The tubes should not be shaken. Vigorous mixing may cause foaming or hemolysis making the sample useless. Insufficient mixing or delayed mixing in serum tubes may result in delayed clotting. In tubes with additives, inadequate mixing may result in platelet clumping, clotting, and incorrect test results.
• After gentle inversion, the serum separator tubes (SST) should be placed vertically in a test tube rack for 30 minutes till the blood clots completely. Short clotting times can result in fibrin formation, which can interfere with complete gel barrier formation.

Centrifugation and Post-centrifugation Handling

Centrifuge at 4000 rpm for 10-15 minutes. Complete gel barrier formation (in the case of gel barrier tubes) is dependent on time, temperature, and gravitational force. The uniformity of the barrier is time-dependent. Therefore reduced centrifugation time would result in an incomplete barrier.

Precautions while centrifugation

• Centrifuges must never be operated without a cover in place.
• Tubes should be well stoppered.
• Care should be taken to balance the tubes while placing them in the centrifuge.

• • The weight of buckets, tubes, and their contents on the opposite sides of the rotor should not differ by more than 1%.
  • Opposing tube holders must be empty or loaded with equally weighted samples (tubes of the same size and equal in fill).
  • If an odd number of samples is to be spun, a tube filled with water should be used to match the weight of the unpaired sample and placed opposite to it.

• If abnormal noise or vibration is noted while the centrifuge is in operation, the unit should be immediately stopped and checked for a possible load imbalance.
• For a horizontal, swing-bucket centrifuge, the recommended spin time is 10 minutes. For a fixed-angle centrifuge, the recommended spin time is 15 minutes.
• The speed control switch should be at zero before starting the centrifuge and adjusted to the required speed.
• The lid should not be opened while the centrifuge is in operation.
• The centrifuge should never be slowed down or stopped by grasping part(s) of the device with hands or by applying another object against the rotating equipment. It should be allowed to stop on its own.
• The centrifuge should be cleaned daily with a disinfectant and paper towel. Broken tubes or liquid spills must be cleaned immediately with 1% sodium hypochlorite solution.
• Gloves must always be worn while handling centrifuge and blood samples as any spillage can be hazardous.

After Centrifugation

The serum/ plasma should be physically separated from contact with cells as soon as possible and not later than 2 hours. If left unseparated, analytes shift between the cells and the plasma/serum resulting in erroneous results. Also, glucose gets consumed by RBCs and so blood glucose estimation if performed later on an unseparated serum sample will be fallacious.