9th week of SIP - Immunology

Hi everyone! Is my turn again! These few weeks I am attached to the Immunology department of my laboratory. Sound fun but practically nothing much to do as mainly the tests is done automatically. My lab is using a system called ADVIA Workcell whereby it employ a unique sample handling process that integrates the ADVIA Centaur Immunoassay System and the ADVIA 1650 Chemistry System to manage the patients' samples. In Immunology, the main machine we are using is the ADVIA Centaur Immunoassay System.

Taken from

http://diagnostics.siemens.com/webapp/wcs/stores/servlet/ProductDisplay~q_catalogId~e_-111~a_catTree~e_100001,1009257~a_langId~e_-111~a_productId~e_172958~a_storeId~e_10001.htm

The tests which are done in the Immunology Department are for infectious diseases (e.g. HIV, Hepatitis, HCV, etc.), fertility (e.g. Prolactin, Progesterone, Follicle Stimulating Hormone, etc.) Thyroid Function (e.g. Free T4, Free T3, TSH, etc.), and more (can't possibly name everything out.). Some are scheduled tests; some are tests that are run everyday. And of course, my department also does Dengue Testing. But I will more focus on the HIV testing using ADVIA Centaur Immunoassay System as the samples are the most in the department and it has it own Centaur machine (just for running HIV).

IMMUNOLOGY - HIV TESTING

Human Immunodeficiency Virus (HIV) is a retrovirus that can lead to Acquired Immunodeficiency Syndrome (AIDS), a condition whereby the human's immune system begins to fail, leading to life threatening opportunistic infections. HIV primary infects vital cells in the human immune system such as T-helper cells, macrophages and dendritic cells. It will lead to al low level of CD4+ cells number to decrease below critical through direct viral killing of infected cells, increase rate of apoptosis in infected cells and killing of infected cells by lymphocytes that recognizes the infected cells. This will cause the cell mediated immunity will lost and the body will increase susceptibility to infection. Infection can occur through several routes such as unprotected sexual intercourse, contaminated needles, transmission from infected mother to her baby at birth or through feeding breast milk. Treatment is now available but it will only prolong life span of the person but cannot fully cure the person.

The assay used for testing HIV is HIV 1/O/2 enhanced assay (EHIV). The samples we need to test for HIV is the patients' serum (preferably from plain or EDTA tube). This assay is an in vitro diagnostic immunoassay for qualitative determination of antibodies to HIV Type 1, Group O, and/or Type 2 in serum. The assay is an antigen bridging microparticle cheminluminescence immunoassay used for the detection of antibodies to the HIV in serum.

Principle of the Assay:

It is a two wash antigen sandwiched immunoassay in which antigen are bridge by the antibody present in the patient sample. The Solid Phase contains a preformed complex microparticles and the HIV antigen. This reagent is used to capture anti-HIV Type 1 and Type 2 recombinant antigen that is used to detect anti-HIV antibodies bound to the Solid Phase in the patient's sample.

Before Automation Steps are performed by the machine, some steps need to done manually:

• Order the test by batch (by rack number). Note that each rack can only contain 5 sample tubes.
• Remove the caps of the sample tubes and make sure the appropriate barcode is pasted on it and the volume of the serum is sufficient. If not, the serum need to be aliquot out into a new test-tube with the patient barcode pasted on it.
• Place the sample tubes on the 1st rack ordered and place in the machine. Make sure the tubes sit in properly to prevent prop crashed.
• Place the last few tubes on the last rack ordered. In between any racks can be used, meaning that the racks that are used in between the two racks ordered will be tested for HIV.
• Then the machines will take in the racks one by one.

Automatic steps that are performed by the machine:

• 50ul of patient's serum will be aliquot out form the sample tube into a cuvette and incubate for 6 min at 37°C.
• Reagents will be aliquot into the cuvette and incubate again for 18min at 37°C.
• The cuvette will then wash with Wash 1.
• Another reagent will then be aliquot into the cuvette and incubate for 18min at 37°C.
• The cuvette will then wash with Wash 1 again.
• Acid Reagent and Base Reagent will then aliquot into the cuvette to initiate cheminluminescence reaction.

Reference Range:

• Reactive is more that 0.9
• Non-reactive is less that 0.9

If Reactive:

• Repeat the testing again. Spin down the sample tube at 10000rpm for 10 min, aliquot the serum out into a new test tube with appropriate barcode, then rerun in another machine.
• If repeat test is negative, report as "Not Detected".
• If repeat test is positive, call clinic to inform Doctor that Western Blot need to be done for confirmation.
• If Western Blot is negative, attached the report to screening report and send directly to Doctor.
• If Western Blot is positive, reports need to be notified to referring Doctor via phone and the report will be sent directly to the Doctor in a confidential envelope and CDC will be informed.
• The reactive samples will be sent to hospital for Western Blot test.

No wonder Ye Tun, you tell me that you received samples from my lab. You all should know where the Western Blot is done by now.... Hope my post helps you all to understand HIV testing. Feel free to ask me questions.

Lizzie Chew, TG01, 0503194C