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Blood borne pathogens

Why is screening for blood borne pathogens important?

Blood borne pathogens, including the viruses(BBVs) like hepatitis B, hepatitis C, HIV and syphilis, are a serious public health concern because they are readily transmitted during sexual intercourse, sharps injury or needle sharing.

The early stages of infection are often silent and during this period, transmission to others can take place unknowingly. With effective treatments now available for syphilis and other blood borne viruses, these pathogens can be controlled and patients cured.

Diagnostic tests that allow accurate and prompt detection and effective clearance of these pathogens are essential contributors to patient management, patient wellbeing, and public safety. However, not all patients are aware that they are carriers.

Community interventions that do not need appointments at GP or hospital clinics require community solutions to screening populations at risk, eg at pharmacists and drug and alcohol centres, prison screening programmes, HIV at-risk population screening and hepatitis C eradication programmes. For these to succeed, novel approaches to blood screening without the need for phlebotomy services are crucial.

Blood borne pathogen testing at South West London Pathology

South West London Pathology (SWLP) has developed an innovative solution to blood borne pathogen screening using capillary blood testing. Capillary blood testing involves taking a small blood sample (approximately eight drops of capillary blood) from a puncture on the finger using a safety lancet and processing this sample with dilution techniques, without altering test sensitivity and specificity.

It is particularly useful for those patients who are difficult to bleed (including babies and infants) and in the home testing setting. . The patient or an assistant lances a finger-tip and collects 250 µL of capillary blood (8 to 10 drops of blood) directly into a paediatric EDTA tube. They then recap and shake the tube to prevent clotting. The sample is stable for four days and can be sent back to the laboratory for testing by post or courier if at distance, and by collection within SWLP locations.

What are the advantages of capillary blood testing at SWLP?

Capillary blood testing (CBT) is less invasive and requires smaller amounts of blood than venous sampling by phlebotomy.. Samples can easily be taken in the community and sample quality is retained by additives in the sample tube. The sample remains liquid and retains the ability to offer quantitative results for infectious disease pathogen monitoring. Due to the UKAS-accredited dilutional techniques involved, multiple tests can be carried out on a single CBT sample which includes antibodies, antigens and either DNA or RNA testing on the same capillary blood sample.

Currently, we are testing CBT samples for:

  • HIV 1&2 antibody/p24 antigenHCV antibody
  • HBsAg
  • HB core total antibody
  • treponemal antibody (for syphilis testing)
  • HCV RNA viral load

HCV RNA positive samples are tested for HCV genotype.. Other nucleic acid tests, eg HBV DNA viral load or HIV RNA viral load can be substituted for HCV RNA viral load if preferred. Although antibody and antigen results are relatively unaffected by the dilutional techniques employed the lower limit of detection of HCV, HIV and HBV for viral load tests is 225 iu/ml and lower limit of quantification is 300 iu/ml.

The combination of both serological and molecular testing from one sample, on fully automated and verified equipment and assays, means that a further confirmatory test is usually unnecessary. The turnaround time for the test is four working days. Single target testing for HIV or HCV of HBV or syphilis screening can be accommodated on request.

Find out more

If you are interested in finding out more about this test or partnering with SWLP please email SWLPBusinessDevelopment@stgeorges.nhs.uk.

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