Background
Exposure to beryllium (Be) can lead to Be sensitisation (BeS) and chronic beryllium disease (CBD). Diagnosis of BeS and CBD rely on the lymphocyte proliferation test (LPT) which is generally performed on mononuclear cells from peripheral blood (PBMC) or bronchoalveolar lavage (BAL). LPT is generally accepted to distinguish CBD from sarcoidosis. We present our findings since we started using the test.

Material an Methods
We retrospectively analysed LPT results and medical records of all patients who underwent LPT at our institution between 12/2002 and 07/2022.

Results
We included 431 patients with available LPT results, totalling 1234 tests (1084 from PBMC, 150 from BAL). Patients had generally known or likely occupational Be exposure, most commonly in the fields of metal working and dentistry. The LPT revealed BeS for 170 patients of whom at least 87 fulfilled criteria for CBD. 106 patients had sarcoidosis. The sensitivity and specificity of a single positive LPT were 53.4% (CI 49.3-57.3) and 94.9% (CI 92.6-96.5). When LPT from both PBMC and BAL were performed, BAL-LPT was positive in 17 cases (44.2%) with negative test from PBMC, emphasizing that its sensitivity might be higher. FVC was worse in CBD than in sarcoidosis (87.1% ± 22.8 vs. 98.5% ± 18.5 predicted; p<0.01). A restrictive phenotype was more frequent in CBD (n=20) than in sarcoidosis (n=7; p=0.02; OR=3.3 (CI 1.2-8.3)).

Conclusion
The threshold to use the LPT in a context of granulomatous disease and possible Be exposure should be low. In many such cases we could confirm CBD. In the absence of a more sensitive test, the LPT remains our best option. A high suspicion of CBD despite negative LPT should prompt repeat testing. BAL-LPT can further improve the diagnostic yield.