Investigation of Abnormal Operation of Specimen for Interferon-Gamma Release Assay, Ilan County, 2018

From July to August, 2018, four events of latent tuberculosis infection tests using Interferon-gamma release assay in Ilan county were rejected and were requested for re-sampling by the laboratory because of specimen clot. To figure out the cause of clotting, we investigated the procedures of sampling and transferring of specimen by checklist. The results showed that the storage environment of tubes and tube-shaking method were improper and needed to be modified. After culturing, some of the purple tubes showed obviously clumping. However, there were no indeterminate results in all specimens, which suggested that the clot read by the laboratory staff might be interfered by the diseases of the patients and the storage time of the specimens. Therefore, the time to check clot of specimens should be done while sampling by the medical technicians. Laboratory staff should suggest re-sampling only when the results show indeterminate outcomes, which could avoid unnecessary stress and workloads on public health officials.