Type of test Microbiology culture

 Normal findings

 Negative for TB

Test explanation and related physiology

 Diagnosis of TB can be made only by identification and culture of Mycobacterium tuberculosis in a specimen. Conventional culture techniques for growth, identification, and susceptibility of acid-fast mycobacteria take 4 to 6 weeks. Because a patient suspected of having TB cannot be isolated for that duration, the disease may spread to many other people while he or she waits for the diagnosis. With the resurgence and increasing incidence of TB in the U.S. population (especially among immunocompromised patients with AIDS), newer, more rapid culture techniques have been identified and are now being performed.

The BACTEC method is a culture technique in which the growth medium for culturing mycobacteria is supplanted with a substrate labeled with radioactive carbon (¹⁴C). This substrate is used by mycobacteria; during metabolism, radioactive carbon dioxide (¹⁴CO2 ) is produced from the substrate. The ¹⁴CO2 is detected and quantitated. This permits quick identification of mycobacterial growth.

PCR culture methods have also been developed. With the addition of a DNA polymerase, genetic chromosomal parts can be multiplied. This allows amplification of genomes, which then can be detected by genetic DNA probes. With these newer techniques, M. tuberculosis can be identified in as few as 36 to 48 hours. With this reduction in diagnostic time, treatment can be started earlier.

When TB is suspected, a sputum smear for AFB can be obtained. After taking up a dye, such as fuchsin, M. tuberculosis is not decolorized by acid alcohol (i.e., it is acid fast). It is seen under the microscope as a red, rod-shaped organism. If this bacillus is seen, the patient may have active TB. Other specimens, such as cerebrospinal fluid, tissue, and synovial fluid, may be used. AFB is also used to monitor treatment for TB. If after adequate therapy (2 months), the sputum still contains AFB (even though the culture may be negative because of anti-TB drugs), treatment failure should be considered.

Interfering factors

 * Antituberculosis drugs

 Procedure and patient care

Before

* Explain the procedure to the patient.

* Tell the patient that no fasting is required.

 During

• For sputum collection, it is best to induce sputum production with an ultrasonic or nebulizing device. Collect three to five early morning sputum specimens. All specimens must contain mycobacteria to make the diagnosis of TB.

• For urine collection, obtain three to five single clean-voided specimens early in the morning.

• Swabs, intestinal washings, and biopsy specimens should be transported to the laboratory immediately for preparation.

• Note the following procedural steps:

 1. When the specimen is received by the laboratory, a decontamination process is applied to it to kill all nonmycobacteria. The specimen is then cultured in the appropriate medium.

 2. With the rapid growth techniques, the specimen is evaluated every 24 hours.

3. When culture growth is considered adequate, the organ isms are stained for AFB and identified.

4. With genetic probes, the Mycobacterium species is identified.

 5. At this point, if M. tuberculosis is present, the report will read “culture more positive for mycobacteria.” If the species has been identified, this also will be reported.

 6. Drug-susceptibility testing then will be carried out and subsequently reported.

After

* Instruct the patient as to appropriate isolation of sputum and other body fluids to avoid potential spread of suspected TB.

 Abnormal findings

- Tuberculosis

- Atypical mycobacterial nontuberculosis disease

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم شؤون المعارف يطلق دورة (صفات الشيعة) لعدد من ملاكات العتبة العباسية المقدسة

الهيأة العليا لإحياء التراث تبحث تعزيز التعاون المشترك مع مركز الإمام الباقر (عليه السلام) في إيران

جامعة الكفيل تكرِّم طلبتها المتميزين من ذوي الاحتياجات الخاصة

فريق طبي في مستشفى الكفيل يجري عملية ناجحة لطفل يعاني من تشوّه ولاديّ بالنخاع الشوكي

المزيد

الآخبار الصحية

خصوصا مع تقدم السن.. 6 سلوكيات يومية قد تدمّر صحتك

فاكهة خضراء.. علاج طبيعي فعّال للإمساك واضطرابات الهضم

روسيا تبدأ أولى التجارب السريرية للقاح واعد ضد السرطان

كنز غذائي على طبقك.. ماذا تفعل السبانخ بجسمك؟

المزيد

الآخبار التكنلوجية

رصد نوع نادر من القطط في تايلاند للمرة الأولى منذ عقود

روسيا تخطط لإقامة محطة نووية في القمر خلال العقد المقبل

كيف قاد إيلون ماسك حملة "غروك" لاختراق عرش الذكاء الاصطناعي

ألتمان: الذكاء الاصطناعي سيتجاوز البشر في 2026 !

المزيد

مواضيع ذات صلة

marijuana (THC) test (Cannabinoid or cannabis testing, Tetrahydrocannabinol [THC] testing)

lung cancer molecular testing (AKT1, ALK, BRAF, Epidermal growth factor [EGFR], HER2, KRAS, MEK1, MET, NRAS, PIK3CA, RET, and ROS1)

kidney stone analysis (Urinary stone analysis, Renal calculus analysis)

Variability and Standardization of CSF Examination

Lab Diagnosis of Yellow fever

hexosaminidase (Hexosaminidase A, Hex A, Total hexosaminidase, Hexosaminidase A and B)

hemoglobin electrophoresis (Hgb electrophoresis)

growth hormone stimulation test (GH provocation test, Insulin tolerance test [ITT], Arginine test, Glucagon Stimulation test)

Markers of Bone Resorption: Amino and Carboxy-Terminal Telopeptides of Collagen Type I

Markers of Bone Resorption: Collagen Cross-Links

Bone Formation Markers : Osteocalcin

Diagnosis of Prion Disease