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Evidence of TB bacteria

TB tests look for evidence of these TB bacteria, Mycobacterium tuberculosis, © NIAID

The development of TB disease is a two-stage process. In the first stage, known as latent TB, a person is infected with TB bacteria. In the second stage, known as active TB or TB disease, the bacteria have reproduced sufficiently to usually cause the person to become sick. Some tests are for latent TB, others are for active TB, and some are for both.

A diagnosis of active TB disease can only be confirmed when there is definite evidence of TB bacteria in the person’s body. Some of the TB tests, such as the skin test, look directly for TB bacteria. Others such as the chest X-ray look for the effect of the bacteria on the person suspected of having TB

The accuracy of TB tests

Some of the current tests take a long time to obtain a result, and some tests are not very accurate. The tests either have low sensitivity (the ability to correctly detect people with TB) and/or low specificity (the ability to correctly detect people who haven’t got TB).

If a TB test has low sensitivity, it means that there will be a significant number of “false negatives”, meaning that the test result is suggesting that a person has not got TB when they actually have. Similarly, a low specificity means that there will be a significant number of “false positives” suggesting that a person has TB when they actually don’t.

The most accurate tests such as culture take a long time to do. Some tests are also very expensive and require complex laboratory facilities.

Culture Test

Although the culture test for TB is very accurate, it can take several weeks to get a result. It also requires expensive equipment and skilled personnel.

Reporting Takes 6 weeks – 1320 MRP
Different culture tests:

The skin test

The skin test is a widely used test for diagnosing TB. In countries with low rates of TB it is often used to test for latent TB infection. The problem with using it in countries with high rates of TB infection is that the majority of people may have latent TB.

The skin test involves injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm. Then the person must return after 48 to 72 hours to have a trained health care worker look at their arm. The health care worker will look for a raised hard area or swelling, and if there is one then they will measure its size. They will not include any general area of redness.

A health care worker measures the size of the reaction to the tuberculin skin test © CDC

The test result depends on the size of the raised hard area or swelling. The larger the size of the affected area the greater the likelihood that the person has been infected with TB bacteria at some time in the past. But interpreting the TB skin test result, that is whether it is a positive result, may also involve considering the lifestyle factors of the person being tested for TB.2 The TB skin test also cannot tell if the person has latent TB or active TB disease.

The Mantoux TB test is the type of TB test most often used, although the Heaf and Tine tests are still used in some countries. None of these tests though will guarantee a correct result. False positive results happen with the skin test because the person has been infected with a different type of bacteria, rather than the one that causes TB. It can also happen because the person has been vaccinated with the BCG vaccine. This vaccine is widely used in countries with high rates of TB infection. False negative results particularly happen with children, older people and people with HIV.

48-72 hours for Reporting – MRP 225 RS
Different skin tests:

SP60480	Mantoux Test (01 TU) Tuberculin test	PPD	2 ml of serum
SP63940	Mantoux Test (02 TU) Tuberculin test	PPD	2 ml of serum
SP63941	Mantoux Test (05 TU) Tuberculin test	PPD	2 ml of serum
SP63942	Mantoux Test (10 TU) Tuberculin test	PPD	2 ml of serum

TB Interferon gamma release assays (IGRAs)

The Interferon Gamma Release Assays (IGRAs) are a new type of more accurate TB test. In this context referring to an assay is simply a way of referring to a test or procedure.

T-SPOT® TB Test © Oxford Immunotec

IGRAs are blood tests that measure a person’s immune response to the bacteria that causes TB. The immune system produces some special molecules called cytokines. These TB tests work by detecting a cytokine called the interferon gamma cytokine. In practice you carry out one of these TB tests by taking a blood sample and mixing it with special substances to identify if the cytokine is present.

Two IGRAs that have been approved by the U.S. Food and Drug Administration (FDA), and are commercially available in the U.S., are the QuantiFERON® TB Gold test, and the T-SPOT® TB test. The advantages of an IGRA TB test includes the fact that it only requires a single patient visit to carry out the TB test. Results can be available within 24 hours, and prior BCG vaccination does not cause a false positive result. Disadvantages include the fact that the blood sample must be processed fairly quickly, laboratory facilities are required, and the test is only for latent TB. It is also thought that the IGRAs may not be as accurate in people who have HIV. In low prevalence resource rich settings, IGRAs are beginning to be used in place of the TB skin test.

MRP – 2750 and Special Lab Rate: 1500 INR
IGRA TB test:

OT40474	IGRAs (Interferon-Gamma Release Assay) QuantiFERON-TB Gold	ELISA	Blood in special container (lithium heparin)	Mon, Wed & Fri: 7 am

Sputum smear microscopy

A sputum smear stained using fluorescent acid fast stain © CDC/R W Smithwick

Smear microscopy of sputum is often the first test to be used in countries with a high rate of TB infection. Sputum is a thick fluid that is produced in the lungs and the airways leading to the lungs. A sample of sputum is usually collected by the person coughing.

To test for TB several samples of sputum will normally be collected. In 2012 it was suggested that two specimens can be collected on the same day without any loss of accuracy.

To do the TB test a very thin layer of the sample is placed on a glass slide, and this is called a smear. A series of special stains are then applied to the sample, and the stained slide is examined under a microscope for signs of TB bacteria.

Sputum smear microscopy is inexpensive and simple, and people can be trained to do it relatively quickly and easily. In addition the results are available within hours. The sensitivity though is only about 50-60%.9 In countries with a high prevalence of both pulmonary TB and HIV infection, the detection rate can be even lower, as many people with HIV and TB co-infection have very low levels of TB bacteria in their sputum, and are therefore recorded as sputum negative.

Different sputum smear microscopy tests:

MB20472	Sputum for AFB Test	Rapid AFB Cold Method	Sputum	Daily:12 pm	Reporting after 3 days	220
MB20503	Sputum for AFB Test (3 Days)	Rapid AFB Cold Method	Sputum	Daily:12 pm	Reporting after 3 days	550
MB21067	Sputum for AFB Test	Rapid AFB Cold Method	Sputum	Daily:12 pm	Reporting after 3 days	935
MB20513	Sputum for Culture and Antibiotic Sensitivity	Aerobic culture & automated AST	Sputum	Daily:12 pm	Reporting after 3 days	770

Fluorescent microscopy

The use of fluorescent microscopy is a way of making sputum TB tests more accurate. With a fluorescent microscope the smear is illuminated with a quartz halogen or high-pressure mercury vapour lamp, allowing a much larger area of the smear to be seen and resulting in more rapid examination of the specimen.

One disadvantage though is that a mercury vapour lamp is expensive and lasts a very short time. Such lamps also take a while to warm up, they burn significant amounts of electricity, and electricity supply problems can significantly shorten their life span. One way of overcoming these problems is the use of light emitting diodes (LEDs). These switch on extremely quickly, have an extremely long life, and they don’t explode.

In 2011 the World Health Organisation issued a policy statement recommending that conventional fluorescence microscopy should be replaced by LED microscopy. It also recommended that in a phased way, that LED microscopy should replace conventional Ziehl-Neelsen light microscopy.

Differen fluorescent microscopy tests:

SP70017	AFB detection by smear examination Fluroscence Microscopy BAL & other respiratory samples	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Same day, 7 pm	660
SP70018	AFB detection by smear examination Fluroscence Microscopy Body fluids	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Next day, 7 pm	660
SP70019	AFB detection by smear examination Fluroscence Microscopy Pus, abscess and aspirates	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Next day, 7 pm	660
SP70020	AFB detection by smear examination Fluroscence Microscopy Sputum - 1 sample	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Next day, 7 pm	660
SP70021	AFB detection by smear examination Fluroscence Microscopy Sputum - 3 samples	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	4th day, 7 pm	1600
SP70022	AFB detection by smear examination Fluroscence Microscopy Tissue and biopsy	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Next day, 7 pm	660
SP70023	AFB detection by smear examination Fluroscence Microscopy Urine - 1 sample	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	Next day, 7 pm	660
SP70024	AFB detection by smear examination Fluroscence Microscopy Urine - 3 samples	Flourescent stain and microscopy	Sterile leak-proof container	Daily: 9 am	4th day, 7 pm	1600
SP70025	AFB detection by smear examination ZN Stain Sputum - 1 sample	ZN stain and microscopy	Sterile leak-proof container	Daily: 9 am and 3 pm	Next day, 7 pm	220
SP70026	AFB detection by smear examination ZN Stain Sputum - 3 samples	ZN stain and microscopy	Sterile leak-proof container	Daily: 9 am and 3 pm	3rd day, 7 pm	550

Chest X-ray as a TB test

If a person has had TB bacteria which have caused inflammation in the lungs, an abnormal shadow may be visible on a chest X-ray. Also, acute pulmonary TB can be easily seen on an X-ray. However, what it shows is not specific. A normal chest X-ray cannot exclude extra pulmonary TB.

Also, in countries where resources are more limited, there is often a lack of X-ray facilities.

A man receives a chest X-Ray during the admission process at a hospital in India. © David Rochkind

MRP 400 Special Discount Rate 375

Serological tests for TB

Serological tests for TB are tests carried out on samples of blood, and they claim to be able to diagnose TB by detecting antibodies in the blood. However, testing for TB by looking for antibodies in the blood is very difficult.

As a result serological TB tests, sometimes called serodiagnostic tests, for TB are inaccurate and unreliable.  The World Health Organisation has warned that these tests should not be used to try and diagnose active TB. Some countries have banned the use of serological or serodiagnostic tests for TB.

Serological tests for TB are very different from the IGRA tests described above.

Different serological tests:

SP60947	ADA Adenosine Deaminase Ascitic Fluid	Biochemical	2 ml ascitic fluid in plain	Daily: 9 am to 1 pm	Next day, 7 pm	Used for diagnosing tuberculosis	880
SP60947	ADA Adenosine Deaminase CSF	Biochemical	2 ml CSF	Daily: 9 am to 1 pm	Next day, 7 pm	Used for diagnosing tuberculosis	880
SP60947	ADA Adenosine Deaminase Pedicardial Fluid	Biochemical	2 ml CSF	2 ml pericardial fluid in plain	Next day, 7 pm	Used for diagnosing tuberculosis	880
SP60947	ADA Adenosine Deaminase Peritoneal Fluid	Biochemical	2 ml CSF	2 ml peritoneal fluid in plain	Next day, 7 pm	Used for diagnosing tuberculosis	880
SP60947	ADA Adenosine Deaminase Pleural Fluid	Biochemical	2 ml CSF	2 ml pleural fluid in plain	Next day, 7 pm	Used for diagnosing tuberculosis	880
SP60947	ADA Adenosine Deaminase Pus	Biochemical	2 ml CSF	Pus in sterile container	Next day, 7 pm	Used for diagnosing tuberculosis. Reference range not established.	880
SP60947	ADA Adenosine Deaminase Serum	Biochemical	2 ml serum	Pus in sterile container	Next day, 7 pm	Used for diagnosing tuberculosis	880

Molecular tests for TB

Some new molecular tests such as the Genexpert test and the TrueNat test are now beginning to be available. Though they are too expensive to be widely used in many countries, the control of TB in South Africa is starting to show what is possible.

TB tests summary

There is no single test that can be used to test for TB in all circumstances. Some tests are cheap but not very accurate. Some can only be used to test for TB and cannot test for drug resistance. Others such as the  TB culture test, the new Genexpert TB test and the TrueNat test can be used to diagnose TB and they can also test for some types of TB drug resistance.

With the development of the new molecular tests there is a beginning to significant progress in diagnosis. However it is unclear why the implementation of these tests cannot be faster. Although there are some issues about the speed with which patients are provided with treatment after receiving a diagnosis, faster diagnosis must surely be a key factor in controlling the TB epidemic in poor resource countries.

Drug susceptibility testing - Molecular tests, Line Probe Assay

What is drug susceptibility testing?

Agar culture plates reveal the results of a drug susceptibility test. © CDC

Drug susceptibility testing means testing to find out if a person has got drug resistant TB. That means finding out which drugs the TB bacteria in their body are sensitive to. It is essential that if a person might possibly have drug resistant TB, that this is discovered as soon as possible, in order that the patient can be provided with effective TB treatment. Historically drug susceptibility testing has been done through culturing the bacteria. It has needed specific laboratory facilities and trained personnel. In addition it is a very lengthy process. There are however now some new tests available one of which is the Genexpert test. This is much easier to use, but it only provides limited information about drug resistance.

Different types of drug susceptibility tests

Drug susceptibility tests for TB are basically of two different types. One type of test is culture, which involves looking at how the bacteria behave. For example, do the bacteria  grow in the presence of anti TB drugs? Another type of test involves looking at genetic mutations.

Molecular drug susceptibility tests

Since resistance arises from genetic mutations, this approach is to detect the mutations themselves. Many mutations associated with resistance have been identified and molecular tests to detect them have been developed. The advantages of molecular methods of drug susceptibility testing include rapid turnaround times, but the disadvantages include a low sensitivity for some compounds, and a major issue is cost.

It is generally perceived that specialist staff is required in order to perform molecular assays. However, some assays such as the Genexpert are extremely easy to use. They can even be taken out of the laboratory setting and used as a “near” point of care test.

Different molecular drug susceptibility tests:

SP70040	AFB-MOTT antibiogram panel For rapid Growers Upto 10 drugs	Broth Microdilution	5 ml of pure culture	Wed & Sat: 7:30 am	15th day	Treatment history required. Identification of Mycobacterium species is compulsory prior to susceptibility testing.	8250
SP70041	AFB-MOTT antibiogram panel For Slow growers Upto 10 drugs	Broth Microdilution	5 ml of pure culture	Wed & Sat: 7:30 am	15th day	Treatment history required. Identification of Mycobacterium species is compulsory prior to susceptibility testing.	9350
SP70043	AFB-Mtb antibiogram Amikacin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70044	AFB-Mtb antibiogram Capreomycin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70045	AFB-Mtb antibiogram Clofazimine	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70046	AFB-Mtb antibiogram Ethambutol	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70047	AFB-Mtb antibiogram Ethionamide	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70048	AFB-Mtb antibiogram Isoniazid	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70049	AFB-Mtb antibiogram Kanamycin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70050	AFB-Mtb antibiogram Levofloxacin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70051	AFB-Mtb antibiogram Moxifloxacin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70052	AFB-Mtb antibiogram Ofloxacin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70053	AFB-Mtb antibiogram Pyrazinamide	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70054	AFB-Mtb antibiogram Pyrazinamide	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70055	AFB-Mtb antibiogram Rifabutin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70056	AFB-Mtb antibiogram Rifampicin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70057	AFB-Mtb antibiogram Streptomycin	Automated BACTEC MGIT 960	3-5 ml of pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	Treatment history required. Request to be sent within 4 days of positive culture report.	2640
SP70058	AFB-Mtb antibiogram panel 1st and 2nd Line panel 10 drugs	Automated BACTEC MGIT 960	5 ml pure culture bottle or tube	Daily: 7.30 am	Upto 4 weeks	Includes SIREP and 2nd Line (4 drugs) panel and Capreomycin	10450
SP70059	AFB-Mtb antibiogram panel 1st Line (4 drugs) SIRE	Automated BACTEC MGIT 960	5 ml of pure culture	Daily: 7.30 am	Upto 4 weeks	Includes Streptomycin, Isoniazid, Rifampicin, Ethambutol	5170
SP70060	AFB-Mtb antibiogram panel 2nd Line (4 drugs) KEPO	Automated BACTEC MGIT 960	5 ml of pure culture	Daily: 7.30 am	Upto 4 weeks	Includes Kanamycin, Ethionamide, PAS, Ofloxacin	6380
SP70061	AFB-Mtb antibiogram panel Additional drugs - 4 nos. MACC	Automated BACTEC MGIT 960	5 ml of pure culture	Daily: 7.30 am	Upto 4 weeks	Includes Moxifloxacin, Amikacin, Capreomycin, Clofazamine	6160
SP70052	AFB-Mtb antibiogram panel Comprehensive panel 13 drugs	Automated BACTEC MGIT 960	Pure culture (Mtb complex)	Daily: 7.30 am	Upto 4 weeks	SIREP, 2nd Line 4 drugs and additional 4 drugs	14300

Beacon Assays

Beacon assays detect M. tuberculosis complex and associated rifampicin resistance directly from sputum samples using ultra sensitive PCR. The Genexpert TB assay is an automated real time based system that has a number of advantages including the fact that it is a closed tube system. The WHO is encouraging the use of the Genexpert TB test, but it has a number of disadvantages including cost.

Different beacon assays:

MB43925	GeneXpert-AFB	Real-Time PCR	Sputum	Daily: 12 pm	2 Days	2750	Special lab rate 2000
MB44734	GeneXpert-AFB (Others Samples)	Real-Time PCR	Others	Daily: 12 pm	2 Days	3300	Special lab rate 2500

Line Probe Assays

Line probe assays are tests that use PCR and reverse hybridization methods for the rapid detection of mutations associated with drug resistance. Line probe assays are designed to identify M. tuberculosis complex and simultaneously detect mutations associated with drug resistance. One of the disadvantages with these assays is that they have an open-tube format, which can lead to cross contamination and an increased risk of false positive results.

Different line probe assays (PCR):

SP70027	AFB detection of DNA by Real-time PCR BAL and other respiratory samples	Real-time PCR	Full bronchial lavage in container	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70028	AFB detection of DNA by Real-time PCR Body Fluid	Real-time PCR	Body fluid in sterile container	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70029	AFB detection of DNA by Real-time PCR CSF	Real-time PCR	CSF in sterile container	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70030	AFB detection of DNA by Real-time PCR Pus, abscess and aspirates	Real-time PCR	Pus in sterile container	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70031	AFB detection of DNA by Real-time PCR Sputum	Real-time PCR	Morning sputum of 3 consecutive days	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70032	AFB detection of DNA by Real-time PCR Tissue and biopsy	Real-time PCR	Tissue in saline	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750
SP70033	AFB detection of DNA by Real-time PCR Urine	Real-time PCR	Morning urine sample of 3 consecutive days	Daily: 7.30 am	Next day, 7 pm	Diagnosis of tuberculosis	2750

Line Probe Assay (LPA) technology is suitable for use at national/central reference laboratories, or at laboratories where there is proven capacity to conduct molecular testing. There must be adequate and appropriate laboratory infrastructure and equipment. This must also include the necessary biosafety precautions and the prevention of contamination. Appropriate laboratory staff also need to be trained to conduct LPA procedures.

Different line probe assays (Hain’s Test):

SP70038	AFB MDR screen Hain's Line Probe Assay Extrapulmonary samples	Line probe assay (Hain's Test)	-	Mon : 9 am	3rd day, 7 pm		1980
SP70039	AFB MDR screen Hain's Line Probe Assay Sputum, BAL, other respiratory samples	Line probe assay (Hain's Test)	Morning sputum of 3 consecutive days	Mon : 9 am	3rd day, 7 pm	Done for both smear-positive and negative pulmonary samples / pure cultures	1980
SP70042	AFB-MOTT Speciation Additional species by Hain's Line Probe Assay Pure culture	Line probe assay (Hain's Test)	5 ml of pure culture	Mon & Thu: 9 am	Next day, 7 pm		3750
SP70063	AFB XDR Screen Hain's Line Probe Assay Extrapulmonary samples		-	Mon : 9 am	3rd day, 7 pm	Test done for smear-positive pulmonary samples / pure cultures	5500
SP70064	AFB XDR Screen Hain's Line Probe Assay Sputum, BAL, other respiratory samples	Line probe assay (Hain's Test)	Morning sputum of 3 consecutive days	Tue: 9 am	Next day, 7 pm	Test done for smear-positive pulmonary samples / pure cultures	5500