[Analysis of stimulating factors for serum copeptin based on liquid chromatography-tandem mass spectrometry]

Copeptin， as a stable surrogate biomarker for arginine vasopressin （AVP）， plays an important role in the differential diagnosis of polyuria-polydipsia syndromes. Current guidelines recommend dynamic monitoring of copeptin levels during stimulation tests to assist in differentiating AVP deficiency （AVP-D） from primary polydipsia. Although these methods are well-established， they have certain limitations. Therefore， safer and more feasible stimulants with reliable effects are of clinical interest. Additionally， the currently available copeptin assay， which is based on time-resolved immunofluorescence assay， can be subject to interference from autoantibodies or hemolysis. This study aims to evaluate the effects of four common stimulants used in growth hormone function tests， namely levodopa， insulin， glucagon， and octreotide， on copeptin levels using a reliable liquid chromatography-tandem mass spectrometry （LC-MS/MS） method developed in our laboratory. A total of 62 subjects undergoing growth hormone function tests were retrospectively enrolled and stratified by stimulation type： levodopa （n=28）， insulin-induced hypoglycemia （n=7）， glucagon （n=20）， and octreotide （n=7）. Blood samples were collected at baseline， 30， 60， 90， and 120 min （for the glucagon stimulation test， samples were collected at 120 and 180 min） for growth hormone determination. Copeptin levels at each time point were measured using LC-MS/MS. The effects of stimulation and correlations were analyzed using the Wilcoxon paired signed-rank test， Mann-Whitney test， and Spearman correlation analysis. The results demonstrated that copeptin levels increased under levodopa stimulation by a maximum of 8.47-fold of baseline （p<0.000 1）， under insulin stimulation by a maximum of 5.85-fold of baseline （p=0.031 2）， under glucagon stimulation by a maximum of 1.43-fold of baseline （p<0.000 1）， and decreased under octreotide to 43% of baseline （p<0.05）. No significant correlation was observed between copeptin level changes and those in growth hormone levels. In the levodopa-stimulation group， the maximum value of copeptin in patients with AVP deficiency was significantly lower than that in non-AVP deficiency patients （p=0.000 2）， and the area under the receiver operating characteristic curve was 0.98 （95% confidence interval 0.94-1.00， p=0.002 1）. Our results demonstrate that levodopa and insulin can effectively stimulate copeptin secretion， whereas octreotide exhibits a suppressive effect. These findings offer important physiological insights into AVP regulation and indicate that certain GH stimulation agents may have extended utility in copeptin-based diagnostic strategies. The LC-MS/MS method for detecting copeptin has potential clinical value in the diagnosis of patients with AVP deficiency and can provide a new detection method for clinical practice. However， the relatively small sample sizes restrict the statistical power， and larger prospective studies are warranted.