TB Testing

TB – it’s a disease you might think has been eradicated if you live in North America … until you apply to volunteer at a hospital.

Mycobacterium tuberculosis is a bacterium that can cause a contagious disease called tuberculosis (TB), where transmission occurs through breathing, coughing, and sneezing of infected people. A challenge with this bacterium is its ability to hide-out in the lungs and wait for an opportune moment to cause disease in its host. This latent form of TB is not transmittable and does not cause immediate disease in the host. The disease progression means there is a great importance for accurate and informative testing processes for latent and active TB.

There are three key reasons a person may be tested for TB – firstly, if there is reason to suspect they may have TB disease; secondly, if a person is immigrating to another country; or thirdly, those working in the health care field. In the case of immigration, the country accepting an applicant may have reason to suspect TB infection based on geography, thus, the testing process could be very similar to the first scenario. Thus, there are some strengths in the current testing process but opportunities for improvements shown through two case studies.

Case 1: Patient suspected that they may have TB disease

To begin, understanding a person’s immunization history is key. In areas of the world with high TB incidence, the BCG vaccine is administered to infants, hours after they are born (See map). This type of medical background information guides Health Canada recommendations. Health Canada recommends the interferon gamma release assay (IGAR) test for those who have been vaccinated twice or have had the Bacille Calmette-Guérin (BCG) vaccine administered after the age of 1 years old. Otherwise, a one-step or two-step tuberculin skin test (TST) is conducted.

Screenshot 2016-07-31 20.29.28

The World Bank incidence data presented on a global map.

The primary difference between the IGAR and TST test is the specificity for the antibodies measured. The TST was created in the early 1900s and are still used today. There may be false positives for those with prior immunization, but there may not. Thus, the IGAR was created in order to provide a more specific test. The IGAR does not measure any of the same strains of Mycobacterium tuberculosis as the BCG vaccine contains.

Case 2: TB test as a requirement for employment or volunteering opportunities

To volunteer in some hospitals, you may require a two-step TB skin test (TST). The requirement for the second test is in order to avoid false negatives. Given the options available the TST is the gold standard for health care providers. It is used to provide a baseline prior to starting one’s occupation. Then it can be used for retesting at regular intervals or in the case of potential contact with an infected patient.

When a TB test is positive

Thus far in the story, TB tests are useful for identifying people with latent TB, but are not effective means of identifying those with active TB. Next steps are required to determine if the individual has a false positive, latent TB, or active TB. Those working in the medical field require a chest X-ray in order to demonstrate the absence of active TB. Those who with positive TB tests and some combination of abnormal chest X-rays or TB infection symptoms will have culture or acid-fast bacteria smear tests conducted. These final tests are the only method for truly identifying those with active TB disease.

Assessment of TB testing

Some success has come from the ease and repetitive ability of TST, financial success can be seen in the innovation of a more specific blood test (IGAR). However, there is room for improvement in the testing process. There are still uncertainties of false negative and positive test results in both TST and IGAR. Moreover, there are many screening steps prior to accurate diagnosis for those who may require treatment. Some steps require more expertise or improved facilities that are not consistently available globally.

For more information:

The Public Health Agency of Canada

Centers for Disease Control and Prevention and their publication

More Quick facts

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Roles of Essential Vitamins and the Consequences of Their Deficiencies

WHAT ARE VITAMINS?

Vitamins are essential nutrients needed by the body in small amounts, to allow the body to grow, develop and function normally. Although our body can make some of its own vitamins, we get the majority of the vitamins we need from the food we eat every day1. In total, there are 13 vitamins needed by the body, and they come in 2 types that are transported and stored differently in the body. These are water-soluble and lipid-soluble.

WATER-SOLUBLE

Water soluble vitamins dissolve in water and are able to move around freely in the body through the blood. These vitamins are found in watery portions of fruits, vegetables and grains. Water-soluble vitamins are not stored in the body. The body takes the vitamins needed from the food and the remainder is disposed of through the kidneys. This means that water soluble vitamins need to be regularly replenished as part of our daily diet. On the other hand, fat-soluble vitamins need fat in order to dissolve. These vitamins require special protein carriers to be transported in the blood. There are many types of water-soluble vitamin but two most common ones are Vit B and Vit C.

VITAMIN B

There are eight types of Vit B and most of them come from our diet. Due to their various types, they can be found in a variety of sources. In animals, they are abundant in fish, meat, and dairy products, and for vegetables, leafy green vegetables, beans, and peas are good sources of Vit B2. In terms of their roles, Vit B perform two main functions in the human body, which are: 1. to make energy from the ingested food; 2. To make red blood cells. It important to note that some Vit B types only perform one of the functions but there are also others types that can have both functions. So what happens when we dont have enough Vit B. Deficiency in Vit B lead to one or more diseases depending on the number of types of Vit B deficiency. For example, deficiency in Vit B12 and 6 can cause anemia, which is an insufficient red blood cells, whereas deficiency in B1 and B3 leads to mental confusion2.

VITAMIN C

The main function of Vit C is to protect you from infections, to grow and repair of tissues, bone, teeth, and skin3. In terms of the best sources of vitamin C, they are fruits, especially guava, papya and orange; and vegetables, such as peppers and broccoli. Deficiency in Vit C causes scurvy, whose symptoms are brown spots on the skin, bleeding from mucous membranes and collagen becomes unstable. Chronic Vit C deficiency causes more severe symptoms, which are pus from open wounds, loss of teeth, and even death.

LIPID-SOLUBLE

Fat-soluble vitamins are stored in fat cells when excess vitamin is present in the diet, to be used at a later time. However, this can be a problem when too much of fat soluble vitamin accumulates to toxic or unsafe levels: a condition known as hypervitaminosis4.

VITAMIN A

Vitamin A’s main role in the human body is maintaining and protecting vision. It is critical for vision as it is a component of rhodopsin, a protein that detects and absorbs light in the eyes. There are two main sources of vitamin A: 1) animal sources, including fish meat, liver, eggs, 2) leafy green vegetables, orange and yellow vegetables, and fruits. The top 3 choices are 1) squash 2) carrot and 3) spinach5. A deficiency in vitamin A is usually rare since most foods contain a least a small amount of it. Vitamin A deficiency is usually more prevalent in developing countries like Nigeria and India where access to foods is more restricted. Deficiency is more common during periods of high nutritional demand such as infancy and childhood. One of the most common symptoms of vitamin A deficiency is xerophthalmia or the inability to see in low light or darkness.

VITAMIN D

Vitamin D is also known as the “sunshine vitamin” because it’s produced in your skin in response to sunlight. You can also get vitamin D from supplements and a very small amount comes from some foods, such as salmon. What makes vitamin D unique compared to other vitamins, is that when your body gets its vitamin D, it turns vitamin D into a hormone. This hormone is sometimes called “activated vitamin D”. The newly activated hormone has many crucial functions to the human body: ensures proper function of important organs, promotes immunity to infection, and most importantly, regulates the absorption of calcium and phosphorous for bone development. Thus, even if you eat lots of foods that contain calcium and phosphorus, without enough vitamin D, you can’t absorb them into your body. As one may predict, too little vitamin D results in softening of the bones, this disease is known as (rickets) in children and osteomalacia in adults6.

 

References:

  1. Moss, A. J., Levy, A. S., Kim, I., & Park, Y. K. (1989). Use of vitamin and mineral supplements in the United States: current users, types of products, and nutrients. Advance data from vital and health statistics174.
  2. Duthie, S. J., Whalley, L. J., Collins, A. R., Leaper, S., Berger, K., & Deary, I. J. (2002). Homocysteine, B vitamin status, and cognitive function in the elderly. The American journal of clinical nutrition75(5), 908-913.
  3. Levine, M., Conry-Cantilena, C., Wang, Y., Welch, R. W., Washko, P. W., Dhariwal, K. R., … & Cantilena, L. R. (1996). Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance.Proceedings of the National Academy of Sciences93(8), 3704-3709.
  4. Rana, M., Wong-See, D., Katz, T., Gaskin, K., Whitehead, B., Jaffe, A., … & Lochhead, A. (2015). Fat soluble vitamin deficiency in children with cystic fibrosis in NSW. Pathology47, S53.
  5. Wolbach, S. B., & Howe, P. R. (1925). Tissue changes following deprivation of fat-soluble A vitamin. The Journal of experimental medicine42(6), 753-777.
  6. Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine,357(3), 266-281.

 


Tiffany is a graduated student in biochemistry and economics who is passionate about research and medicine. She hopes to become a clinical medical researcher in the future. Throughout her undergraduate degree, Tiffany has gained extensive research in both web lab and clinical medicine. She has 2.5 years of wet lab research in which yielded 3 publications, and 1 year of clinical research experience in which she led a group of undergraduate and medical students. She loves to answer any questions, whether it is research, academic or extra curricular related.