Ziehl-Neelsen (ZN) Stain Test
800 Kshs | Home Collection Available
Synonyms
None
Purpose
Laboratory professionals use the Ziehl-Neelsen (ZN) stain test a microscopic technique to detect acid-fast bacilli (AFB), primarily Mycobacterium tuberculosis, in clinical specimens such as sputum. They apply a special staining process that highlights bacteria retaining the red dye even after acid-alcohol treatment, a defining feature of AFB.
This test is critical for the rapid diagnosis of tuberculosis (TB), especially in resource-limited settings, because it is quick and highly specific for mycobacteria. Early detection allows for prompt treatment and helps prevent the spread of tuberculosis, particularly in high-risk populations.
To enhance diagnostic accuracy, the ZN stain test is often performed alongside Sputum culture for Mycobacterium tuberculosis, GeneXpert MTB/RIF test, Tuberculin Skin Test (TST), Chest X-ray, Interferon-Gamma Release Assays (IGRA), and HIV testing.
These complementary tests help confirm the diagnosis, determine the stage or type of TB, and guide treatment decisions.
Patient Preparation
The sputum should be evenly spread over the central area of the slide using a continuous rotational movement.
Samples
5 – 10ml of Sputum collected in a sterile screw-cap container. First morning specimens are preferred due to overnight accumulation of secretions. Refrigerate at 2°C to 8°C.
Reference Range
Sputum smear is graded as scanty, 1+, 2+, and 3+. No AFB seen while observing more than 300 fields reported as No AFB seen. 1-9 AFB/100 fields report the exact number. 10-99 AFB/ 100 fields reported as 1+. 1-10 AFB/field at least in 50 fields reported as 2+. More than 10 AFB/field at least in 20 fields reported as 3+
Results Turnaround
1 – 2days after receipt of samples.
Diseases / Diagnostic indicators
The Ziehl-Neelsen stain test helps detect acid-fast bacilli (AFB) in clinical specimens, which may serve as the initial evidence of mycobacterial infection.
Some possible outcomes of the test include;
Positive Result:
If AFB are observed under the microscope, it suggests a mycobacterial infection, most commonly:
- Tuberculosis (TB) – caused by Mycobacterium tuberculosis
- Leprosy – caused by Mycobacterium leprae
A positive result usually prompts further confirmatory testing (e.g., culture or PCR) and immediate medical intervention, especially if the person is symptomatic.
Negative Result:
If no AFBs are detected, it may indicate:
- Absence of infection
- Very low bacterial load (early-stage or latent TB)
- Poor-quality sample or inadequate staining
In such cases, additional testing (e.g., GeneXpert, culture, or repeat smear) may be necessary, particularly if clinical symptoms persist.
This test plays a vital role in early screening and diagnosis of TB and leprosy, helping to prevent transmission and initiate timely treatment. For more on the Ziehl-Neelsen (ZN) Stain Test, read this study.