Membrane-enriched acid-fast staining solution

What is sample concentration?

Sample concentration is a processing step before testing: bacteria dispersed in sputum or another sample are first brought together, then smeared and stained or passed to another test, so that more target bacteria reach the field of view. Membrane concentration is the membrane-based method, in which bacteria are concentrated and retained on the membrane surface.

How does a concentrated smear differ from a direct smear?

A direct smear is made by spreading the sample straight onto a slide and staining it. A concentrated smear first concentrates the bacteria and then prepares the slide, so more target bacteria from the same sample reach the field of view and low-bacillary-load samples are easier to detect. In a study of 4,114 clinical samples (Tuberculosis 2022), membrane-enriched smears had a sensitivity of 79.4%, compared with 60.5% for direct smears.

Source: Tuberculosis 2022 original study

How does membrane concentration differ from concentration by centrifugal sedimentation?

Centrifugal sedimentation requires taking the sediment from the bottom of the tube before making a smear. In membrane concentration, the embedded-adsorption membrane on the slide inside the sandwich-cup lid concentrates and retains acid-fast bacilli on its surface during centrifugation, and the membrane goes with the slide straight into slide preparation, staining and reading. This reduces losses from centrifugal sedimentation and repeated transfers, and the field of view has less background interference.

What equipment does a clinical laboratory need for sample concentration?

It depends on the chosen method and specimen volume. Centrifugal sedimentation methods can usually use the laboratory's existing centrifuge; the membrane-concentration route needs concentration cups, slide-preparation and staining equipment, and a microscope (100× oil-immersion objective, preferably with a halogen light source). Tianqi's acid-fast staining pathway can combine the sandwich cup, the TQ-12 automatic centrifugal slide-preparation instrument, the LR-24 staining instrument and scanning and review equipment as needed. We recommend assessing the configuration against daily specimen volume and staffing.

Source: Group standard T/CHATA 044—2024, Technical and operating specification for acid-fast staining of membrane-concentrated smears

How are acid-fast bacilli inactivated in membrane-concentration pretreatment?

T/CHATA 044—2024 specifies adding 2–4 times the sputum sample volume of digestion-inactivation solution (containing a sodium hypochlorite disinfectant at a concentration >5% and a protein-lysing agent) at room temperature; mixing and digesting for 30 min inactivates acid-fast bacilli. Procedures should meet the biosafety requirements of WS 233—2017 and WS/T 442—2024.

Source: Group standard T/CHATA 044—2024, Technical and operating specification for acid-fast staining of membrane-concentrated smears

Questions and answers last reviewed October 28, 2026.