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. For all tests:
- a) Check with the patient that s(he) has correctly followed any necessary preparation such as fasting.
- b) The patient should be resting, and seated or lying comfortably, ideally for 5 – 10 minutes before sample collection.
- c) 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.
- d) 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.
- e) Tubes with additives must be thoroughly mixed by GENTLY inverting (not shaking) the tubes 5 - 10 times each.
- f) 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.
3. Centrifugation and sample separation from cells: general information.
- a) 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.
- b) 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.
- c) Certain tests may have additional preparation requirements: please see the Test Guide before collecting and processing samples for a given test or tests.