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Culture Specimen Processing: Advantages and Disadvantages of NALC-NaOH Method
Learning ObjectivesAdvantages and disadvantages of NALC – NaOH Method
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In the N-Acetyl-L-Cysteine - Sodium Hydroxide (NALC-NaOH) method:
- NaOH works as a decontaminating agent.
- Sodium citrate binds with the heavy metal ions that might be present in the specimen, that could inactivate NALC.
- NALC works as a mucolytic agent that allows NaOH to be used at a lower final concentration of 1% and aids in liquefying sputum to release the trapped bacilli.
Advantages of NALC – NaOH Method
- Less number of tubercle bacilli are killed due to lower final concentration of 1% NaOH in the specimen compared to 2% in Petroff’s method
- Higher rates of Mycobacterium Tuberculosis (MTB) culture positivity
- Rapid digestion at a lower concentration of NaOH, due to inclusion of NALC
- Specimens processed with this method are suitable for inoculation onto both solid and liquid medium, since pH is adjusted with phosphate buffer.
Disadvantages of NALC – NaOH Method
- NALC must be freshly prepared as it loses its activity rapidly in solution.
- Extreme agitation of NALC in the presence of NaOH will destroy the activity of NALC.
- Trisodium citrate, in the decontamination solution to bind the heavy metal ions, could inactivate NALC.
- Increased NaOH exposure time leads to over-killing of TB bacilli present in specimen.
Resources
- MGIT Procedure Manual, Mycobacteria Growth Indicator Tube (MGIT) Culture and Drug Susceptibility Demonstration Projects, FIND Training Manual.
- GLI Training Module on Specimen Processing, Stop TB Partnership.
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