Week Number Eight

Hellohello!!! How are you ppl doing? I hope you guys are doing great. This week, it is my turn again to share my experience. For the past few weeks, I have been rotating about, going to a different lab every week. Quite a lot to absorb for such a short period, but I’ll manage.

I was posted to an infectious disease testing lab one of the weeks. For your information, upon donation, a few samples of blood will be collected from donors to undergo testing, such as infectious disease testing, blood group testing and antibody screening. Under infectious disease itself, it is further divided into a few sections. And the section I am going to explain is TPHA lab.

TPHA is the short form for Treponema pallidum (TP) haemagglutination assay. TP causes Syphilis which is a sexually transmitted disease. The route of transmission is almost always through sexual contact. However, it can also be transmitted through blood transfusions. Therefore, it is important to screen all donors for TP so as to prevent any harmful transmissions and transfusions.

In the TPHA lab, the machine used is the ABBOTT ARCHITECT Syphilis TP. Its intended use is for the diagnosis of Syphilis.

PRINCIPLE OF ASSAY

1. The ABBOTT ARCHITECT Syphilis TP assay is a two-step immunoassay for the qualitative detection of antibody to Treponema Pallidum (TP) in human serum or plasma using Chemiluminescence Microparticle Immunoassay (CMIA) technology with flexible assay protocols, referred to as Chemiflex.
   
2. In the initial step, sample and microparticle coated with recombinant TP antigens (TPN15, TPN17, TPN47) together with the Assay Diluent are combined. Anti-TP antibodies present in the sample bind to the TP coated microparticles. After washing, the acridinium-labelled anti-human IgG and IgM conjugate is added in the second step. Following another wash cycle, Pre-Trigger and Trigger Solutions are added to the reaction mixture.
   
3. The resulting chemiluminescent reaction is measured in relative light units (RLUs). A direct relationship exists between the amount of Anti-TP antibodies in the sample and the RLUs detected by the ABBOTT ARCHITECT i optical system.
   
4. The presence or absence of Anti-TP antibodies in the sample is determined by comparing the chemiluminescent signal in the reaction to the cutoff signal determined from the ABBOTT ARCHITECT Syphilis TP calibration. If the chemiluminescent signal in the sample is greater than or equal to the cutoff signal, the sample is considered reactive for Anti-TP.
   

The specimen used for this assay is either serum or plasma. Haemolysed samples should not be used and all fibrin clots or bubbles must be removed before loading of samples

In the event where there is a positive result, confirmatory tests must be performed. Serum or plasma samples will be collected in a tube and sent to the Serology Laboratory, Department of Pathology, Singapore General Hospital (Reference Laboratory).

The following confirmatory tests are ordered for the determination of the donor’s infection status:

a) Treponema pallidum Particle Agglutination (TPPA) test – an alternative treponemal screening test
b) Venereal Disease Research Laboratory (VDRL) test – a non-treponemal test to determine current or recently treated infection status
c) LIA(Line Immuno Assay) – Syphilis (LIA) – as the confirmatory test for the presence of treponemal antibodies

I hope what I have shared this time round has been a beneficial one. 12 more weeks to go and back to school!! Alright, time to go... see ya

Rusydiana binte Kusni
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