Biomnis >> Test Information >> Pre-analytics

Pre-analytics

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The vast majority of erroneous results are caused by errors made during sample collection and transport, rather than to analytical errors within the laboratory. For this reason it is essential that correct procedures are followed for patient preparation, sample collection, sample preparation (e.g.: centrifugation) and sample transport. For information regarding our sample packaging instructions please click here. The following procedures should always be followed; additional procedures and processes may be required for specific tests. These will be indicated in the description of the test in the printed Test Guide and on the Eurofins Biomnis website at: http://www.eurofins-biomnis.ie/TestMenu/TestGuide.aspx.

1. Patient identification. We require at least two identifiers for every patient, both on the request form and on each sample tube. A minimum of the following are required: surname and given name, plus one of the following: Patient ID, date of birth, laboratory number. If these are not present, the samples cannot be processed.

2. Sample collection: Blood/Serum/Plasma

  • Check with the patient that s(he) has correctly followed any necessary preparation such as fasting.
  • The patient should be resting, and seated or lying comfortably, ideally for 5 – 10 minutes before sample collection.
  • The tourniquet or blood pressure cuff should be left tightened or inflated for as short a time as possible, ideally less than 30 seconds but certainly not more than 1 minute.
  • If more than 1 type of sample tube is to be used, they should be collected in the following order:
    • i. Blood culture bottles.
    • ii. Tubes without additives (yellow or red top) for serum.
    • iii. Heparin tubes (green top).
    • iv. EDTA tubes (purple top).
    • v. Coagulation tubes (light blue top). NB: these must be completely filled up the indicator line. Incompletely filled coagulation tubes will be rejected for analysis as they lead to incorrect results.
    • vi. Oxalate/fluoride (light grey top) for glucose.
  • Tubes with additives must be thoroughly mixed by GENTLY inverting (not shaking) the tubes 5 - 10 times each.
  • Certain tests (such as dynamic function tests, very labile analytes) will have additional special procedures. Please see the Test Guide before collecting and processing samples for a given test or tests.

Centrifugation and sample separation from cells: general information.

  • Serum (yellow or red top tubes) should be allowed to clot completely at room temperature before centrifugation: 30 – 60 minutes.
    • i. Centrifuge for 10 minutes at 1300 g in a swing-out rotor.
    • ii. For tests stable at room temperature: serum in plain tubes (i.e.: still in contact with cells after centrifugation) must be transferred to a plain secondary tube without additives. Gel-separator tubes may be sent as is to the laboratory. NOTE: samples for therapeutic drug monitoring should ideally be taken into a plain tube without separator gel. Some drugs may adsorb to the gel in tubes from some manufacturers, giving inaccurate results.
    • iii. For tests requiring refrigeration or freezing: transfer the serum to a plain secondary tube without additives or gel, then refrigerate or freeze as appropriate for the required test, for transport to the laboratory.
  • Plasma: tubes with anticoagulants should be thoroughly mixed by gentle inversion 5 – 10 times immediately after sampling.
    • i. They must then be centrifuged for at least 15 minutes at 2 000 to 3000 g in a swing-out rotor to obtain a cell-free plasma.
    • ii. After centrifugation, plasma must be removed from the cell pellet and transferred to a plain secondary tube which can then be refrigerated or frozen as required for transport to the laboratory.

Quantiferon TB Gold Plus Samples:

  • Label tubes appropriately and ensure strictly 1 ml of blood is taken into each tube.
  • Immediately after filling tubes, gently invert them 10 times to ensure the entire inner surface of the tube is coated with blood, to solubilise antigens on tube walls.
  • Samples should be transferred to a 37°C incubator as soon as possible, and within 16 hours of collection.
  • Prior to incubation, maintain the tubes at room temperature (22°C ± 5°C).
  • Do not refrigerate or freeze the blood samples prior to incubation.
  • Incubate the samples upright at 37°C for 16-24 hours.
  • Following incubation, within 3 days, samples should be centrifuged for 15 minutes at 2000 to 3000 RCF (g).
  • The gel plug will separate the cells from the plasma. If this does not occur, the tubes should be centrifuged again at a higher speed.
  • Samples may remain at between 4-27°C prior to centrifugation within 3 days and 2-8°C post centrifugation.
  • All quantiferon samples received in the laboratory should be accompanied by a request form and a Quantiferon TB Information Form (available here)

3. Sample Collection: Urine

Random, untimed urine collections are usually taken for microbiological testing (culture and sensitivity). For most biochemical tests, timed samples (usually 24-hour) are required.

Random samples for microbiology should be collected into a sterile container. The hands must be thoroughly washed and dried before the sample is collected. The sample should be a mid-stream sample, and care should be taken that no part of the body touches the rim or interior of the container before, during or after collection. The lid should be securely fastened to the container immediately after collection.

TIMED SAMPLES: it is essential for interpretation of the results that the urine collection is accurately timed.  A timed collection is collected as follows:

  1. The patient empties his or her bladder and discards this urine.
  2. The time must be noted; this is the time of starting the collection.
  3. ALL urine passed from now until the end of the collection period must be collected into the container.
  4. In order to avoid injury from acid or other preservatives within the container, each sample of urine should be passed into another clean container, and then added to the collection container.
  5. During the collection period, the collection container should be kept in a cool, dry place. A refrigerator at 4 to 8 °C is ideal.
  6. Exactly X hours after the start time (noted as in 2. above; where X is the number of hours of the collection, usually 24) the patient empties his or her bladder and places this sample into the collection container.
  7. The timed collection is now complete.

The sample requirements, including requirements for the patient to avoid certain foods and medications, vary from test to test. Please contact the laboratory for information and the appropriate container.

It is also essential that the correct preservative is placed into the collection container BEFORE the timed collection is started. Again, the preservatives vary from test to test. Please contact the laboratory for information and the appropriate container.

As some of these preservatives can be harmful (especially acids), the patient should, as mentioned above, first pass each voiding of his or her bladder into a separate, clean container, and then immediately transfer this sample into the timed collection container with preservative.

4. Certain tests may have additional preparation requirements: please see the Test Guide before collecting and processing samples for a given test or tests.