AFB-detection by smear examination ZN Stain Urine, 1 samples
Report in 24Hrs
At Home
Details
Primarily used to evaluate urinary tuberculosis (genitourinary TB)
₹149₹500
70% OFF
1000+ Booked this Test
🔬 AFB Detection – ZN Stain (Urine, 1 Sample)
Parameter | Details |
|---|---|
Fasting Required? | ❌ Not required |
Sample Type | Midstream urine sample, early morning preferred |
Sample Volume | At least 10–50 ml to ensure proper sediment concentration |
Primary Purpose | Detect Acid-Fast Bacilli (AFB) such as Mycobacterium tuberculosis |
Target Organs | Kidneys, ureters, bladder, urethra (Genitourinary TB) |
Common Disease | Urinary Tuberculosis (part of Extrapulmonary TB) |
🧪 What is ZN Staining?
The Ziehl-Neelsen (ZN) stain identifies AFB by staining the high lipid cell walls of mycobacteria. AFB retain red carbol fuchsin dye even after decolorization with acid-alcohol, differentiating them from other bacteria.
🧫 Why Use Urine for AFB Smear?
- TB can infect the genitourinary tract, especially in immunocompromised patients.
- Mycobacteria may be shed intermittently in urine, making smear microscopy useful for initial screening.
📈 Interpretation of Results
Result | Bacilli per 100 fields | Interpretation |
|---|---|---|
Negative | 0 | No AFB seen; TB not ruled out |
Scanty | 1–9 | Low bacillary load |
1+ | 10–99 | Moderate infection |
2+ | 1–10 per field | Significant bacillary shedding |
3+ | >10 per field | Heavy infection; high infectivity |
🧠 Clinical Suspicion Indicators
- Sterile pyuria (WBCs in urine with no routine bacterial growth)
- Persistent urinary symptoms (frequency, dysuria) without clear cause
- Flank pain, hematuria, or renal function decline
- Immunocompromised status (e.g., HIV)
⛔ Limitations
Limitation | Explanation |
|---|---|
Low sensitivity (~20–40%) | Due to intermittent shedding and low bacilli concentration |
False negatives common | Particularly with single-sample smears |
Requires skilled microscopy | Operator-dependent accuracy |
Ideally, 3 consecutive early morning urine samples should be tested to improve yield.
🔗 Recommended Additional Tests
Test | Purpose |
|---|---|
Urine AFB Culture (MGIT or LJ) | Gold standard; detects live mycobacteria; drug susceptibility testing |
GeneXpert (Urine TB-PCR) | Rapid detection + Rifampicin resistance |
Ultrasound KUB/CT Urogram | Assess structural renal damage or ureteral strictures |
Urinalysis + Microscopy | May show WBCs, RBCs; suggests inflammation |
Blood Urea, Creatinine | Evaluate renal involvement |
✅ Summary Table
Test Name | AFB Detection – ZN Stain (Urine) |
|---|---|
Sample Required | 1 early morning urine sample, midstream preferred |
Result Timing | Same day (within hours) |
Used For | Detecting urinary/genitourinary TB |
Sensitivity | Low with one sample; better with 3 early morning sets |
Paired With | Culture, GeneXpert, Imaging, Renal function tests |
How our test process works!
