Hey all. It's my turn to share again. For the past 2 weeks, I was attached to the Biochemistry department. Not many samples were received manually in this department as most of the samples were loaded into a sample manager and processed automatically. I believe Maya has explained what is a sample manager in one of her posts previously, so I shall not go into it. Some of the tests done in the department are urine glucose tolerance test, G6PD screening test, HbA1C test and urine drugs screening test. The rest of the tests are loaded in and processed automatically. Most of the automated tests are processed by a machine called the ADVIA 1650 by Siemens Diagnostics. However, for HbA1C test, the samples need to be ordered into the system and loaded in manually.
Retrived 16th August 2008 from, www.clpmag.com/issues/articles/2006-12_09.asp
For Drugs 5 test, one test device is used. The test device is able to test presence of all 5 drugs at one time. For Drugs 7 test, 3 test devices are used. 1 test device testing for the presence of the same 5 drugs, 1 test device testing for the presence of Barbiturates (BAR) and 1 more test device testing for the presence of Benzodiazepines (BZO).
The test is based on lateral flow chromatographic immunoassay to detect presence of the specific drugs and their metabolites. The principle of the test is competitive binding between either the drug present in the urine with their specific antibody or, the drug conjugate with the specific antibody.
3-5 drops of urine are dropped onto the each of the circular wells found at the bottom part of the test device. The urine will then move upwards by capillary action. If the drug is present below the cut-off concentration, the drug conjugate will bind to the specific antibody instead and forms a visible line across. If a visible line is observed, the result is recorded as negative. However, if the drug is present in high amounts and above the cut-off concentration, the drug will bind to the specific antibody instead of the drug conjugate. This will cause no visible line to be observed across and the result is recorded as positive. For every drug tested, there is a region for Control. If there is no visible line observed across at the Control region, the test is then considered invalid and should be tested again using a new test device.
The following figure is a visual interpretation of the results, done using Microsoft Powerpoint.
The cut-off concentrations are as follows for each type of drug:-
Amphetamine - 1000 ng/mL
Barbiturates - 300 ng/mL
Benzodiazepines - 300 ng/mL
Cocaine - 300 ng/mL
Marijuana - 50 ng/mL
Methamphetamine - 1000 ng/mL
Opiate (OPI 300) - 300 ng/mL
The antibodies present on the test devices for each drug type are mouse monoclonal antibody-coupled particles. For each drug test, drug-protein conjugates are also present specific to the drug type. For each Control region, it contains goat anti-rabbit IgG polyclonal antibodies and rabbit IgG.
This urine drugs screening test is only a qualitative test and not a quantitatinve test. Therefore, we are unable to tell the amount or drugs level present. It is also only a screening test. A gas chromatography or mass spectrometry should be carried out to confirm any positive results obtained. A negative result does not necessarily the urine is free of drugs. Other types of drugs not tested for their presence, may also be present. A positive result may also be caused by the kind of food consumed by the patient.
As most of the drugs are controlled drugs, I have never encounter any positive results ever since I have been attached to the Biochemistry department. According to one of the permanent staffs there, it is also quite rare to encounter any postive results as Singapore rules are very tight when it comes to abusing drugs.
I guess that's all for now. If you have any queries to ask, please feel free to do so. I will try to reply as soon as I can. Thank you. C:
Nur Azeimah
0607060A
TG02
4 comments:
August 19, 2008 at 9:26 AM
Hi Azeimah~
That's some new interesting applications you learnt...
If I may ask you a few questions:
1) Regarding the drugs being tested, why are they chosen over other thousands of drugs?
2) For the drug test, the control must be positive in order to accept the results, right?
My question is why would it give positive result?
3) If any positive results are obtained for the drug testing, what would happen next?
Hope you could help clear my doubts.
Many thanks
Quan Jun
TG02
Group 08
19 August 2008
August 20, 2008 at 9:45 PM
Hi Azeimah
That's a very comprehensive post=)
Just a short qns,
do u know if there is a specific reason why they test for this 5 or 7 kinds of drugs and not the other kinds?
Thanks
Zhenling
TG02
August 21, 2008 at 10:59 PM
hi QJ,
1) the test kits ordered by the company i'm attached to, are only able to test for the 5 or 7 drugs. the drugs are chosen probably because they are commonly abused. the samples used are also urine samples, which means, the drugs can be expelled through the urine. i hope that answers your first question because i've tried asking the permanent staffs there but they all couldn't answer it either. sorry.
2)the control should turn out negative. i believe you typed wrongly in your question. reason is, a negative result will show a visible line. a positive result will show NO visible line. if the control is positive, and shows no visible line, we wouldnt be able to differentiate between an invalid test or a valid test then. i hope you get what i mean.
3)usually, we would report to the specific clinics/doctors if any postive result is obtained. it is up to the doctor to order for a more specific or another confirmatory test to be carried out then. i believe i've mentioned what are the types of confirmatory tests. they are gas chromatography or mass spectrometry.
thank you.
Nur Azeimah
0607060A
TG02
August 21, 2008 at 11:02 PM
hi zhenling,
your question is similar to QJ's first question. i hope you can refer to my explanation there. thank you.
Nur Azeimah
0607060A
TG02
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