Protocol for AFB smear staining

By Cedric Cheung | 09 Oct, 2016

Dear all,
Though it may be old fashioned, we here at our hospital can still only do AFB staining for detecting AFB in sputum samples. I am not a lab person, but as I understand it, the gold standard protocol involves digestion, decontamination, and centrifugation (using a 50 mL size centrifuge). The lab is not even processing the specimens but only taking sputum and directly smearing it on the slide and doing the staining. As expected, the yield for positive bacilli is quite low (actually zero). The lab does have a 10 mL size centrifuge (and will not be able to purchase a 50 mL one), my question to everyone is: does anyone have a protocol using a smaller size centrifuge?
Thanks for any help!
Cedric Cheung
Sichuan, China

Replies

 

Tafara Zanamwe Replied at 5:46 AM, 9 Oct 2016

Dear Cedric
Your situation sounds interesting, perhaps you can share a little bit more about the possibilities available to your lab.
1. Besides microscopy is there any other test that will be performed on the sputum in your lab. (this is useful for choosing method of concentration)
2. can your centrifuge achieve speed of 3000g?
3. What kind of rotor is the centrifuge equipped with (Swing out / fixed angle)?
4. Is the centrifuge refrigerated?
5. What is the current turnaround time for smear microscopy?
6. What is the average number of samples for microscopy performed per day/ month?

Regards

T

Cedric Cheung Replied at 12:10 AM, 10 Oct 2016

Dear Tafara,
Thank you for replying, let me answer your questions:

1. Besides microscopy is there any other test that will be performed on the sputum in your lab. (this is useful for choosing method of concentration): None
2. can your centrifuge achieve speed of 3000g? yes
3. What kind of rotor is the centrifuge equipped with (Swing out / fixed angle)? fixed angle
4. Is the centrifuge refrigerated? no
5. What is the current turnaround time for smear microscopy? 24 hours
6. What is the average number of samples for microscopy performed per day/ month? about 5-8 samples per day

thanks for any suggestions

RAJNEESH TRIPATHI Replied at 3:30 AM, 10 Oct 2016

Dear Cedric Cheung
If u have centrifuge without refrigeration, you may concentrate your
specimen by digesting it but only for *Microscopy strictly not for culture*.
It definitely improved sensitivity 20-30%. Keep in mind that lab should
have Biosafety cabinet.

Jacqueline Limo Replied at 4:09 AM, 10 Oct 2016

You do not need a biosafety cabinet if you are processing few specimens in
the lab, this is according to WHO and a few published reports round the
world. For culture, yes you will require

Ben Bechir L. Beaubrun Replied at 9:16 AM, 12 Oct 2016

Thank you Jacqueline!
--------------------------------------------
En date de : Lun 10.10.16, Jacqueline Limo via GHDonline <> a écrit :

Objet: Re: Protocol for AFB smear staining
À: "Ben Bechir L. Beaubrun" <>

Murtada Osman Replied at 7:28 AM, 2 Nov 2016

Dear Cedric Cheung

Sputum concentration in this situation will not increase the positivity rate (Low postivity among TB suspects) my be due to low prevalence in the community.(For sputum you need 5000-10.000 Bacilli/ml for positive sample which can be detected by microscope).
In my opinion to look for new rapid molecular techniques like(Gen expert or LAMP) because they have high sensitivity and specificity they didn't need Safety Cabinet which can increase the detection rate .
Thanks
Murtada Osman