Sample Acceptance Criteria
Please note: Blood Transfusion has a more stringent labelling policy than Haematology due to increased risk to patients in case of labelling errors. For specific information about Transfusion sample acceptance criteria, please refer to the Blood Transfusion sample acceptance criteria page.
Maximum Sample Volumes
EDTA and citrate anticoagulated sample bottles (Red and green lids) have a fill line printed on them and should not be overfilled, as this can lead to the formation of clots within the sample which invalidates the majority of haematology tests.
Minimum Sample Volumes
Note: All sample bottle plungers should be fully retracted to the bottom of the tube. Plungers that have not been fully retracted will be re-seated at the bottom of the tube before any evaluation of volume is performed.
Underfilled samples can hamper laboratory investigations in a number of ways. Analysers that have liquid level-sensing probes and are set to sample a specified distance under the surface may collide with the bottom of the bottle, potentially putting the analyser out of operation. With sample bottles that contain anticoagulants, too low a volume of blood in the bottle will lead to the blood becoming significantly diluted and making any test results incorrect. Coagulation tests are particularly prone to this kind of error due to underfilling, as the test relies on knowing the exact amount of anticoagulant in any aliquot it takes from the sample so it can reverse the effect back to normal. As such, coagulation samples that are not filled to within 3 millimetres of the fill line are discarded.
Minimum accepted volumes are as follows:
3.4ml EDTA bottle (Red): 1.0ml - Please consider using paediatric EDTA bottles at this volume
1.3ml paediatric EDTA bottle (Red): 0.3ml
3.0ml or 1.4ml Citrate bottle (Green): No more than 3 millimetres below the fill line
4.7ml gel bottle (Brown): As the percentage volume of serum in a blood sample varies between patients, absolute minimum sample volumes cannot be specified. Where applicable, recommended minimum volumes are stated in individual test requirements.
Sample Suitability and Integrity
Specimens must be sent in the correct type of container(s) for the test(s) requested. A list of tests available in Haematology and the corresponding container can be found in the Haematology Test Information section. Alternatively, if a request is made using the Sunquest ICE computer system, the required type and number of specimen containers is printed on the request form.
All possible care must be taken not to contaminate request forms and exterior surfaces of collection tubes with blood or other substances that could present a health and safety risk to those handling them.
Leaking sample bottles will be rejected if they would pose a health and safety risk to those handling them. Coagulation samples which are not leaking but still have visible damage to the sample bottle may also be rejected, if the damage is sufficient to have potentially allowed anticoagulant to leak from the bottle prior to being used. As coagulation tests rely on reversing the anticoagulant effect in the sample, altering the ratio of blood to anticoagulant will cause false test results.
Samples collected into bottles which have passed their expiry date will be rejected.
Factors known to affect Haematology test performance
Factors that may influence test results include phlebotomy, anticoagulant used, specimen transport and storage of samples.
Difficulty in taking blood from the patient or inadequate mixing may result in the sample clotting in the blood tube. This can produce fully clotted samples at one extreme, to microscopic fibrin clots at the other that can be difficult for the laboratory to detect. This can cause misdiagnosis, inappropriate therapy and/or clinical delay.
Effect on Full Blood Count (FBC) – Reduced platelet count due to activation. All parameters can be affected if the clot is removed from the tube before sending to the laboratory, as it will be removing a significant proportion of the blood cells from that sample.
Taking blood from a patient's drip arm can result in a dilution of the blood which will affect all tests results. Taking blood for coagulation tests from a patient's heparin drip arm will result in falsely elevated results due to the presence of extra anticoagulant in the sample.
Transferring blood into the sample bottles from another syringe can cause haemolysis due to the shearing force experienced by the blood as it is forced out through the needle. This can also activate coagulation, leading to falsely shortened clotting times.
EDTA can cause platelet clumping in approximately 1% of patient samples. The effect is variable and can be detected on examination of the blood film. The problem can be overcome by repeating the FBC in a special anticoagulant tube supplied by the laboratory. If this is necessary, please contact the laboratory to arrange for the bottles to be made available.
Blood taken into EDTA anticoagulated bottles will undergo storage changes over time. The red blood cells become misshapen, and the white blood cell count falls as the white blood cells become increasingly fragile. This makes the FBCs of old samples inaccurate, and makes examination of any blood films made from old samples very difficult.
Coagulation tests rely on knowing the exact amount of anticoagulant in any aliquot taken from the sample, so the exact amount of calcium can be added to reverse the effect back to normal. Too much or too little blood taken into the bottle (i.e. not filled to the line on the bottle) will result in there being either too much or too little anticoagulant in the bottle, causing the test results to be incorrect and potentially misleading.
Specimen Transport and Storage
If the specimens are subjected to excessive heat when transported (e.g. left in the window of a car in direct sunlight) then the red and white cells within the sample will fragment. As well as leading to an artificially lowered WBC and RBC, some of the fragments will be mistaken as platelets leading to a falsely elevated platelet count. As such, the FBC will be rejected by the laboratory. Coagulation tests will be falsely elevated due to heat-induced breakdown of the coagulation factors.
Routine haematology samples should ideally arrive in the laboratory and be tested within 6 hours of phlebotomy, with the exception of D Dimer tests which can be performed up to 24 hours after the sample is taken, and INR requests for warfarin monitoring which can be performed up to 48 hours after the sample is taken.