There are many factors that must be considered when obtaining and transporting samples for analysis. Incorrect venepuncture or incorrect transportation and storage of samples, can affect the integrity of the sample and cause erroneous results. Some of these factors may be detected by laboratory staff during processing, but there is a possibility that they may go undetected. Therefore abnormal results with no clinical indication or inconsistent results should be repeated to confirm.
Sample integrity is critical for obtaining accurate patient results. If samples are not treated in an appropriate way, this could cause erroneous results that may not be detectable by the laboratory.
Poor venepuncture can result in haemolysed or clotted samples.
Severe haemolysis results in a falsely low haemoglobin and affects the red cell indices; these samples will be rejected
Insufficient or incorrect mixing of samples, slow flowing blood or samples obtained by non-venous access can cause clots in the sample. These affect the platelet count and may either activate the coagulation factors (resulting in a low APTT) or consume them (grossly prolonged results). Clots may not be detectable in the sample so should be repeated to verify the results.
Excessive heat exposure will cause lysis of red cells and degeneration of white cells. These changes are visible when examining a blood film.
Haemolysis of a sample due to heat exposure, poor venepuncture or excessive mixing will cause erroneous results. These samples should be repeated.
Patient factors such as lipaemic or icteric samples will interfere with some assays, such as DDimer results and, depending on the severity, the RBC indices. In some cases, results may not be obtainable.
Transportation of samples
The correct transportation of samples to the laboratory is essential to maintain sample integrity for analysis. The following points should be considered:
- samples should be sent directly to the department
- storage of samples is not recommended before testing as results may be affected.
- if storage is unavoidable please contact the laboratory for advice
- coagulation samples should be tested within 8 hours of phlebotomy
- coagulation samples must not be refrigerated
- do not expose samples to heat (e.g. hot radiators and car dashboards in Summer)