Culture Specimen Processing: Advantages and Disadvantages of NALC-NaOH Method

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

1. 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
2. Higher rates of Mycobacterium Tuberculosis (MTB) culture positivity
3. Rapid digestion at a lower concentration of NaOH, due to inclusion of NALC 
4. 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

1. NALC must be freshly prepared as it loses its activity rapidly in solution.
2. Extreme agitation of NALC in the presence of NaOH will destroy the activity of NALC.
3. Trisodium citrate, in the decontamination solution to bind the heavy metal ions, could inactivate NALC.
4. 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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