Saturday, August 4, 2007

6th week of SIP - Biochemistry

Hey everyone,

This week, I was posted to the biochemistry lab. The lab consists of 3 sections.

1st section

Consist of the main analyzer Beckman Coulter Synchron LX20 PRO Clinical System. Test for levels of Urea, creatinine, glucose, total protein, AST, GGT, etc. in blood serum.

2nd section

Consist of analyzers to conduct tests such as

  • Blood gas
  • Serum lactate and ammonia test
  • Serum bilirubin
  • HbA1c to test for diabetes
  • G6PD testing
  • Serum and urine osmolality.

3rd section

Also called the ‘urine bench’. Conduct tests such as

  • Urine FEME
  • Fungal test
  • Occult blood

Everyday, we receive the specimens, which comes together with a request form and a sticker label. We check the name and NRIC of the patient and the tests requested on the form. We then centrifuge the specimens for 10mins. However, some specimens for tests like HbA1c and Urine FEME does not require centrifugation. Blood specimens come in a plain tube (contain silicon gel), EDTA tube, or fluoride tube. After centrifugation, we will then process the specimens according to the tests requested.

I will explain more on G6PD testing.

G6PD Testing

  • Blood specimens come in EDTA tube to prevent clotting.
  • Prepare empty tubes for the samples and controls.
  • 3 controls. Deficient control (commercial), intermediate control (commercial), and positive control (patient sample)
  • 100µl of buffer (to lyse the cells) is aliquoted into each tube.
  • Aliquote 5µl of samples into the tubes containing the buffer.
  • Shake the tubes vigorously to mix, then incubate for 10mins to fully lyse the red cells, thus releasing the G6PD enzymes.
  • Prepare the cards to test for fluorescence. On each card, there are blank circles for each sample. Label the sample number and controls on the card, then proceed to aliquot 10µl of the sample solution and controls onto their appropriate circles.
  • Place the cards in an incubator for 10mins to dry the samples, as it will be difficult to see fluorescence if the samples are wet.
  • After incubation, place the cards in a UV illuminator, ‘Model CX-21 Ultraviolet Fluorescence Analysis Cabinet”.
  • The positive control should show fluorescence. Intermediate control should show slight fluorescence, and the deficient control should show NO fluorescence.
  • Check for fluorescence for the samples, to determine if the patient has G6PD deficiency. If they are deficient for G6PD, their sample will show no fluorescence, and these samples will be tested again just to confirm the results.

Theory behind G6PD Test

G6PD is an enzyme found in RBCs. G6PD deficiency is due to labile G6PD enzyme that is present in young cells but rapidly disappears with cell aging. It results in hemolysis after exposure to certain oxidant drugs such as anti-malarials, and also during infections. The disease is transmitted as an X-linked recessive, and is more prone in males.

Alright, that is all for now. Feel free to ask any question. Hope you guys are enjoying yourselves just like me! =D

Out.

Adrian Tan TG01
0503205G

16 comments:

Star team said...

Hello!

I am also in Biochem lab. hmm, in my lab, we centrifuge specimens at 3500rpm for 5 min only.

Why tests like HbA1c and Urine FEME do not require centrifugation?

Jo-anne Loh
TG02

MedBankers said...

hey adrian,

what is the purpose of having the intermediate control?

eunice
TG02

J.A.M.M.Y.S said...

Hi Adrian,

For the G6PD testing right, let's say if the patient does not have G6PD deficiency, the sample will show fluorescence correct? But how come it will fluoresce? Is the G6PD labelled with an antibody conjugated to a fluorescent compound or is the cards that you used are special, meaning that it will fluoresce when there is G6PD?

Ming Boon
Tg01

Star team said...

Hey Adrain

What do you mean by a deficient control?What's the purpose of having it? Thanks =)

Eugene WOng
TG02

Anonymous said...

Hi,
In my lab, the urine FEME is done in the microbiology lab. Does your lab conduct microscopy work on urine with abnormal results from the urinalysis? My lab uses the Urisys 2400 analyse. Is your lab using the same analyser too???

Yeng Ting

we are the XiaoBianTai-7! said...

Hey Jo-anne,

the purpose of centrifugation of blood samples is to separate the RBCs and the serum, and therefore, it is needed for tests that require you to draw out the serum. As for HbA1c testing, purpose is to test for hemoglobins in the blood sample which is found in RBCs, therefore there is no reason to centrifuge the sample prior to testing.

Hey Eunice,

the intermediate control should show slight fluorescence when under UV light. It is used to look for samples that have mild G6PD deficiency. These samples will also show slight fluorescence under UV light. If the intermediate control does not show slight fluorescence, the rest of the results might not be accurate as well.

Hey Ming Boon,

the test is actually called the Beutler fluorescent spot test. This test visually detects the generation of NADPH under ultraviolet light. NADPH will fluoresce under UV light.
In the presence of G6PD, NADP+ will get reduced to NADPH. The rate of NADPH formation is proportional to G6PD activity. In G6PD deficient samples, there will be low NADPH generation, thus no fluorescence.

Hey Eugene,

Deficient controls are commercial blood that are known deficient of G6PD. It is used as a control during the test to ensure that results are accurate and there is no error cause by certain variations. The spot with the deficient control should show no fluorescence due to deficiency in G6PD. If there is fluorescence, it means that there may be some variations and the results may not be accurate. Positive controls are patient samples that are known to have sufficient G6PD (not G6PD deficiency).

Hope these answers your questions =)

Adrian.

we are the XiaoBianTai-7! said...

Hey Yeng Ting,

Yes, microscopy of the urine sample is done if protein, nitrite, WBC, RBC is detected during the test.

I will get back to you on the analyzer name =)

Adrian.

The Lab Freaks said...

hello!

what's the purpose of having silicon gel in the plain tube

Suat Fang
Tg01

royal physicians said...

hello!

are ur controls experimental or technical controls? And what's the main difference between positive and intermediate controls? As in, how do u all choose which one considered positive which one considered intermediate for controls.

Thanks!

Chen Kangting
0503331A
TG02

Kent said...

Yoz dude,

I'm doing G6PD screening for my MP but relax, i wun make things difficult for you.. =P

The question is how will you confirm the results of the G6PD deficiency if the preliminary screening fails. Contrast the difference in test principle of the screening and confirmatory test.

Thanks and enjoy urself!

Kent
TG01
0503261J

we are the XiaoBianTai-7! said...

Hey Yeng Ting,

The analyzer my lab uses is called Roche Miditron M.

Hey Suat Fang,

Not all plain tubes will have silicon gel. The silicon gel acts as a catalyst for blood clotting. It allows faster clotting of the blood.

Hey Kang Ting,

we use a known positive patient sample as the positive control, and commercial blood for the intermediate control. Positive control will give a very obvious bright fluorescence when under UV light, whereas intermediate control will give a faint fluorescence.

Not sure what you mean by technical or experimental, but the controls are there for 2 purposes. Its main purpose is to make sure that the results of the samples are accurate. If the results of the controls show something different than expected, they will have to troubleshoot to determine if there is any technical variations or maybe cross contamination. They will repeat the test again. The other purpose of the controls is for us to compare its results to the results of the samples to determine if the patient has severe G6PD deficiency, mild G6PD deficiency or has normal levels of G6PD.

Hey bro,

Lol. Your MP topic still ask, trying to test me is it? Anyway will get back to you on that.

we are the XiaoBianTai-7! said...

Hey Kent,

my lab do not conduct any confirmatory tests. If there are doubts, meaning the results of the patient sample show mild or severe G6PD deficiency in the fluorescent spot test, the samples will be sent to SGH for quantitation. The amount of G6PD in the blood sample will be quantitated to confirm the results.

Adrian.

Randall said...

hey Adrian,

Can you elaborate more on the principles of the G6PD test?

Thanks,
Randall
TG02

VASTYJ said...

Yo adrian!

wah so many qn le, i shall make mine simple...

u meantion 'blood specimens come in a plain tube (contain silicon gel), EDTA tube, or fluoride tube.', Plain tube and EDTA i know its uses, but wana know what is fluoride tube for?

Chaur Lee
TG01

we are the XiaoBianTai-7! said...

Hey Randall,

The fluorescent spot test used to test for G6PD visually detects the generation of NADPH under ultraviolet light.
If there is G6PD in the blood, NAD+ will get reduce to NADPH, and NADPH will fluoresce under UV light. In G6PD deficient blood, there is also deficient NADPH therefore there is no or very slight fluorescence.


Hey Chaur Lee,

Fluoride prevents enzymes in the blood from working, so a substrate such as glucose will not undergo reactions like glycolysis and get used up during storage.


Adrian.

ALsubs said...

hi !

You mentioned about Occult blood. what is that actually??

And also wat is the fluorescent used in the G6PD test?

Vinodhini
TGO2