Patients with thyroid diseases who are treated with I-131 may be released if the total effective dose equivalent to any other individual from exposure to the released individual is not likely to exceed 5 mSv (0.5 rem) following assessment of the patient’s medical, living and working conditions (32 IL Adm. Code 335.2110). Occasionally, these individuals will need to have blood drawn for unrelated issues several hours to a few days after the administration of I-131. This could present a radiation safety or regulatory issue if protocol is not established for the phlebotomy or laboratory staff. An article discussing the radioactivity of blood in patients treated with I-131 describes measuring methods and the relative radioactivity of blood depending on activity administered, sample volume, and time elapsed. In most cases, for adults with normal kidney function, a 3 ml sample of blood from a patient given a normal therapy dose of I-131 presents little danger to laboratory staff.
Still, in keeping with ALARA, it is recommended to include requirements for monitoring all blood samples drawn from hospitalized patients undergoing treatment with I-131 NaI. Hospital laboratory staff should be advised to contact nuclear medicine personnel in a timely manner prior to performing phlebotomy on treated patients to ensure that blood samples are monitored for elevated radiation levels. Policies should state that if the survey meter reading from a blood sample, or the gloves or lab coat of the phlebotomist, are indistinguishable from background radiation as measured with a survey instrument specified in a license application, no further action will be taken. If a blood sample is above background radiation, further monitoring of laboratory personnel and the area and equipment where the blood sample will be processed should be conducted.