The Tuberculin Skin Test (TST), also called the PPD or Mantoux test, screens for exposure to Mycobacterium tuberculosis. This procedure involves a precise injection and a follow-up assessment, raising questions about which healthcare professionals are authorized to perform each step. The process is highly regulated and involves distinct actions: administering the injection, measuring the reaction, and interpreting the final result. A Medical Assistant’s (MA) role in this sequence is specific and constrained by training and state regulations.
The Medical Assistant’s Role in Test Administration
The initial step of a TST involves injecting a small amount of purified protein derivative (PPD) into the top layer of the skin using the Mantoux method. The Medical Assistant’s role typically begins with preparing the necessary equipment, including a tuberculin syringe and a 26- or 27-gauge needle. The MA cleans the injection site, usually on the inner forearm, and then administers the PPD intradermally, creating a small, pale bump called a wheal.
This administration is a technical procedure MAs are generally trained to perform under the direct supervision of a licensed practitioner. A successful injection requires inserting the needle bevel-up at a shallow angle, ensuring the correct amount of solution (typically 0.1 mL) is delivered. Following the injection, the MA instructs the patient to return for a follow-up appointment, which must occur between 48 and 72 hours later for the test to be valid.
Measuring Induration Versus Interpreting the Result
Whether a Medical Assistant can “read” a TB test depends on the distinction between physically measuring the result and clinically interpreting it. The physical reading involves assessing the injection site for induration, a firm, raised area indicating a delayed-type hypersensitivity reaction. The MA, or any trained healthcare worker, uses palpation and a ruler to accurately measure the diameter of this induration in millimeters (mm), ignoring any surrounding redness.
Medical Assistants are frequently authorized to perform this measurement, recording the size in millimeters or noting “0 mm” if no induration is present. However, interpreting the result—determining if the measurement is positive or negative—is almost always reserved for a licensed practitioner. This includes a Registered Nurse (RN), Physician Assistant (PA), Nurse Practitioner (NP), or Medical Doctor (MD). Clinical interpretation requires synthesizing the measurement with the patient’s individual risk factors, which falls outside the typical scope of an MA.
The threshold for a positive result is not a single number, as it depends entirely on the patient’s medical history and risk of exposure. For instance, an induration of 5 mm or more is positive for an immunocompromised patient or someone with recent, close contact with active TB. Conversely, an induration must often be 15 mm or more to be positive for a person with no known risk factors undergoing employment screening. Since this determination requires clinical judgment regarding factors like BCG vaccination status or immunosuppression, the final diagnosis is a licensed function.
Regulatory Oversight and Scope of Practice
The definitive authority for what a Medical Assistant is legally permitted to do regarding a TST is determined by state law and the specific state’s medical board. MAs are typically considered unlicensed personnel, even if certified or registered, meaning their clinical duties are performed under the direct supervision of a licensed professional. The concept of “delegation” is central to this framework, where a licensed provider entrusts certain tasks to the MA.
State regulations vary widely; some states prohibit MAs from administering tuberculin testing, while others allow it with specific training requirements. Some state medical boards classify the final interpretation of a TST as “practicing medicine,” which cannot be delegated to unlicensed staff. Therefore, while an MA might be permitted to document the physical measurement in millimeters, they cannot independently make the clinical decision that the test is “positive” or “negative.” Readers should consult their state’s specific medical board guidelines, as the scope of practice is location-dependent and subject to the policies of the supervising physician or facility.