Can unstimulated whole salivary flow objectively classify salivary gland secretory function in Sjögren's syndrome?

Introduction: The aim of this study is to investigate whether the testing time for unstimulated whole salivary flow (UWSF) can be shortened to 5 min in patients with suspected Sjögren's syndrome (SjS); and which SjS patients can use UWSF to evaluate salivary gland (SG) secretory function.

Method: A diagnostic cohort comprising suspected SjS patients was conducted to investigate the correlation between UWSF measurements taken at 10 min (UWSF_10 min) and those taken at 5 min (UWSF_5 min). A group of SjS patients was enrolled for a comparison between UWSF and stimulated whole salivary flow (SWSF).

Results: In 734 suspected SjS patients, there was a remarkably high concordance between UWSF_10 min and UWSF_5 min (ICC 0.970, P < 0.001; r 0.973, P < 0.001). Reducing the testing time for UWSF to 5 min resulted in a high PPV of 83.8% and an exceptionally high NPV of 98.7%. In 408 SjS patients, the cut-off values of UWSF_10 min were investigated to classify SG secretory function. Using a threshold of > 0.2 mL/min (36.8%, 150/408) instead of SWSF > 0.7 mL/min (indicating mild secretory hypofunction), the specificity and PPV were found to be 94.2% and 94.0%, respectively; and using a threshold of < 0.05 mL/min (16.9%, 69/408) instead of SWSF ≤ 0.7 mL/min (indicating moderate to severe secretory hypofunction), the specificity was remarkably high at 97.6%, accompanied by a high PPV of 91.3%.

Conclusions: This study supports the possibility of reducing UWSF testing time to 5 min; and the SWSF test may be skipped for SjS patients with USWF > 0.2 mL/min, indicating mild secretory hypofunction, or < 0.05 mL/min, indicating moderate to severe secretory hypofunction. Key Points •A diagnostic cohort of 734 patients with clinical suspicion of SjS provides compelling evidence for the potential to reduce the testing time for UWSF from 10 to 5 min. •Our finding challenges the 2019 treatment recommendation for SjS, which does not require SWSF measurement in SjS patients with UWSF ≥ 0.1 mL/min. •We propose that it may be feasible to consider utilizing UWSF instead of SWSF test for objective classification of SG secretory function in over half of SjS patients.