PCR is a very sensitive and specific method for the direct detection of infectious agents. Via PCR, gene sequences characteristic for the respective pathogen are reproduced and detected – if necessary, even of pathogens which are no longer viable.
The sample material that must be supplied for the PCR highly depends on the pathogen to be detected and the present signs or the diagnostic task. Depending on how the pathogen has spread in the body and its excretion, different sample materials are suitable.
At this stage of infection, pathogens causing viraemia, parasitaemia or bacteraemia can be detected directly in an EDTA blood sample (EB). Lithium heparin is less suitable as an anticoagulant, as it can inhibit the PCR. For blood samples or other liquid samples, an amount of at least 0.2 ml is required.
In contrast to cultural bacteriological/mycological examinations, for PCR tests it is recommended to use sterile swabs without transport medium (swab without medium (A), dry swab). If the concentration of the pathogen is low, swabs in a medium can lead to false negative results. For collecting the sample, the swabs can be moistened with physiological saline solution. For PCR tests, so-called cytobrushes (brush swabs) are also suitable, which can be shipped in an uncoated sterile tube.
For the detection of pathogens in faeces, a sample of approximately the size of a hazelnut is needed. For some agents (e. g. coronavirus, Tritrichomonas foetus) we recommend collecting faecal samples for 3 days, since these pathogens are excreted intermittently in the faeces.
Further sample materials, e. g. skin biopsies, organ material, urine, synovial fluid, CSF, bone marrow aspirates and lymph node aspirates, for PCR tests are best sent in sterile, uncoated test vessels. Fixation solutions such as formalin or the like can lead to DNA degradation, PCR inhibition and thus to false negative results.
Samples do not normally need to be sent cooled. Until it is dispatched, the sample material can be stored in the refrigerator at 2 – 8 °C. Repeated freezing/thawing should absolutely be avoided.
Please note: Creating an antibiogram is not possible after doing a PCR test.