تعليق
Step 3.1 – Select, procure, install and set up equipment
For TB infection skin tests, a stand-alone or medical-grade refrigerator for storing consumables (tuberculin or TB antigens), vaccines and medications must be available. Backup generators or power supply system would also be required. Tuberculin vials should be stored at 2–8 °C (35–46 °F), protected from light, in the original packaging and separated from other similar vials (to avoid confusion). Refrigerators combined with a freezer that have a single door are not suitable. Skin test consumables should not be stored in the door of the refrigerator. Temperature should be monitored using a digital thermometer with the probe inserted in a vial of biosafe glycol or a vial of glass beads. A daily log of temperature, including (where feasible) maximum and minimum temperatures, should be kept. TB infection skin test material that has been exposed to freezing temperatures (below 0 °C) or has been stored above 8 °C should be discarded (56).
Other than the skin test materials, the only consumables needed are gloves, needles, syringes and cotton. Having trained staff is crucial (see Area 4).
For IGRAs, equipped laboratories are needed. Table 4.1 lists the equipment and personnel needed for tests. Tubes, needles, gloves and other material for blood sample collection are also necessary, as are pipettes and other regular laboratory supplies. For T-SPOT.TB, some special supplies are needed, including stains for PBMC counting, positive controls and cell culture media. Equipment such as centrifuges, incubators and optic densitometer also require space, which needs to be considered during planning. Instruments should be properly positioned in a clean, secure and suitable location. Most instruments will require an uninterrupted supply of power, and appropriate working and storage conditions (e.g. humidity and temperature controlled).
For QFT-Plus and WANTAI TB-IGRA, the following equipment is needed: incubator, centrifuge, plate washer, plate agitator and microplate optical density (ELISA) reader. Those are generally available in laboratories that perform other ELISA testing such as serology. The automated QFTPlus testing instrument provides an all-in-one system from loading of the serum to obtaining the result.
For T-SPOT.TB, a biohazard level two cabinet is recommended for initial steps of handling, separating and counting PBMCs. The manufacturer also suggests use of a humidified 37 °C ±1 °C CO2 incubator. In addition, a centrifuge and automatic microplate washer are required, and a lymphocyte counter. Some large volume laboratories have automated spot counters; otherwise, equipment for a technician to count the spots will be required. However, the T-SPOT. TB test can be re-read at any time, which can be advantageous in regions where electricity might be interrupted.
Table 4.1. Equipment and personnel needed for WHO-recommended IGRA tests (8)
ELISA: enzyme-linked immunosorbent assay; ELISPOT: enzyme-linked immunosorbent spot; IGRA: interferon-gamma release assay; QFT-GIT: QuantiFERON Gold In-Tube; QFT-Plus: QuantiFERON-TB Gold Plus; TB: tuberculosis; WHO: World Health Organization.
Step 3.2 – Instrument verification and maintenance
Before starting to use IGRA to test clinical specimens, all instruments, including centrifuges, must be documented as being “fit-for-purpose” through verification with known positive and negative materials. Instrument verification is conducted at the time of installation, after service or calibration, and after moving instruments.
To ensure quality, reproducibility and reliability, maintenance and calibration must be performed regularly. The frequency of calibration and its intervals vary for each instrument. To decide on the frequency of calibration, the recommendations of the manufacturer should be followed at a minimum. However, where the level of accuracy of the equipment is suspected to be declining, those responsible should be able to discern the problem and take the initiative to perform calibration.
Laboratory equipment calibration requires an association between measurements of a scale or accuracy made or set with the equipment to be tested and similar measurements made with the standard (i.e. equipment with known or assigned accuracy). Standards vary from country to country, depending on the type of industry. Manufacturers designate their measurement criterion and recommend the frequency and level of calibration, depending on how often the device is used and the specific application.
Instruments require regular preventive maintenance, and ad hoc servicing and maintenance. The end-user should perform regular preventive maintenance, to ensure that the instrument is performing effectively. Suppliers or authorized service providers should perform on-request maintenance, as necessary. Countries should take advantage of any available extended warranties or service contracts to ensure continued functioning of the instruments.
Instrument calibration is not necessary for performing skin tests; this gives these tests an advantage over IGRAs, although it makes careful training and supervision more important.
Step 3.3 – Assess site readiness and ensure a safe and functional testing site
Each testing site should be evaluated for readiness using a standardized checklist before testing of clinical specimens at the site begins. In addition, existing testing sites should be assessed regularly for safety and operational functionality. This includes training or assessing staff competency to apply tuberculin and read induration (see Area 4) or, in the case of IGRAs, laboratory capacity, phlebotomist availability and the ability to transport samples rapidly (i.e. on the same day) and for the laboratory to deliver results to the providers no more than 48–72 hours after blood collection for IGRA tests.
Appropriate personal protective equipment (PPE) should be used for handling blood samples, and biological waste must be disposed of safely and in accordance with regulations. Biosafety regarding occupational M. tuberculosis transmission is not a concern for TB infection tests. Standard precautions are necessary when handling blood or manipulating needles.