Supplementary Appendix

Transcription

1 Supplementary Appendix This appendix has been provided by the authors to give readers additional information about their work. Supplement to: Fenske W, Refardt J, Chifu I, et al. A copeptin-based approach in the diagnosis of diabetes insipidus. N Engl J Med 2018;379: DOI: /NEJMoa

2 A Copeptin-based Approach in the Diagnosis of Diabetes Insipidus SUPPLEMENTARY APPENDIX TABLE OF CONTENTS METHODS: Exclusion of Patients page 2 Assessment of Adverse Events and Test Burden page 2 Laboratory Analysis page 3 Additional Statistical Considerations page 3 FIGURES Figure S1: Patient flow chart diagram page 5 Figure S2: Relation of Plasma Copeptin to Serum Sodium Levels in Patients with Central Diabetes Insipidus and Primary Polydipsia at the End of the Hypertonic Saline Infusion Test page 6 Figure S3: page 7 A Plasma Copeptin Levels after Overnight Fluid Deprivation B ROC Curve for Plasma Copeptin Levels after Overnight Fluid Deprivation Figure S4: Sodium Change as Function of Volume and Duration of 3% Saline Infusion page 9 TABLE Table S1: Results of Water Deprivation and Hypertonic Saline Infusion-Test on Osmotic Stimulation, Copeptin Release and Urinary Response page 10 REFERENCES page 12 1

3 METHODS Exclusion of Patients Patients with glucosuric polyuria, electrolyte disorders, untreated or insufficiently replaced pituitary-, adrenal- or thyroid deficiency, impaired kidney function or pregnancy were ineligible. For safety reasons, also patients with heart failure, uncontrolled hypertension, or a history of epilepsy were excluded from participation. After enrolment of the first three patients with nephrogenic DI, new data were released 1 confirming that a single measurement of plasma copeptin enables identification of this entity 2. It was therefore decided to no longer recruit patients with suspected nephrogenic diabetes insipidus or to include them into the final analysis. The basal plasma copeptin levels in the three enrolled patients later diagnosed with nephrogenic diabetes insipidus were all within the diagnostic range for nephrogenic diabetes insipidus as previously defined 1,2 (35.9pmol/l, 37.3pmol/l, 23.2pmol/l). Assessment of Adverse Events and Test Burden To compare the subjective inconvenience of both tests, patients were asked to score clinical symptoms (thirst, nausea, vertigo, headache, malaise) by a visual analogue scale (0=no sensation, 10=maximal sensation) during the course of both tests. After completing each test, patients were asked to also rate the subjective test burden via visual analogue scale (0=no discomfort to 10=maximal discomfort), and finally to specify which test they perceived more or less comfortable at the 3-month follow-up visit. 2

4 Laboratory Analysis Blood for plasma copeptin was taken into EDTA tubes, immediately centrifuged at 4 C and stored at -70 C until central analysis in one batch with a commercial automated immunofluorescence assay (B.R.A.H.M.S KRYPTOR Copeptin proavp, Thermo Scientific Biomarkers, Hennigsdorf, Germany) 3. The copeptin assay had a 0.69pmol/L lower detection limit and an inter-assay precision of 20%, with a functional assay sensitivity of 1.08pmol/L. Routine laboratory measurements (urine and plasma osmolality, sodium, potassium, creatinine, urea, calcium, albumin, glucose and haemoglobin, haematocrit) were immediately performed by automated biochemical analyses in the respective local Central Laboratories. Additional Statistical Considerations The full analysis set consisted of the remaining 141 patients. For one patient copeptin samples were lost after the water deprivation test, for another patient after both tests. As for these patients no copeptin-based test diagnoses could be made, we assigned these patients to false diagnoses. The per-protocol set consisted of 139 patients from the full analysis set with no missing test diagnoses. For testing superiority, the 2-sided asymptotic McNemar test for correlated proportions was used. In order to preserve the overall significance level at α = 5%, a p-value <0.025 was considered significant. The superiority tests were performed on the full analysis set (intention to treat analysis). As sensitivity analysis, the superiority test was repeated on the per-protocol analysis. Overall diagnostic accuracy with 95% confidence interval computed according to Blaker 4 is given for each diagnostic test and comparison. All secondary analyses were performed on the full analysis set as complete case analyses. For each of the examined copeptin measurements, the Receiver- Operator Characteristics (ROC) curve is shown. The Area Under the Curve (AUC) with 95% confidence interval computed with Delong s method 5 is indicated. Youden s J statistic 6 was used to determine the post-hoc cut-off with best overall performance. For each predefined and post-hoc derived cut-off the sensitivity, specificity, positive and negative predictive value are estimated with 95% exact binomial confidence intervals, using the R package epir 7. 3

5 Secondary endpoints are presented for each final diagnosis using summary statistics and were tested for a difference using Fisher s exact test (binary endpoints) or Wilcoxon s rank sum test (continuous endpoints). The correlation of plasma sodium and plasma copeptin measured at the end of the hypertonic saline infusion test were analysed using the Spearman s rank correlation coefficient. The presented analyses were all pre-specified in a statistical analysis plan, except for the following post-hoc analyses: comparisons of plasma sodium at the end of the water deprivation test and plasma osmolality at the end of both tests, ROC of change in urine osmolality from before to after injection of desmopressin during the water deprivation test, estimation of diagnostic performance in discriminating the subgroup partial central diabetes insipidus from primary polydipsia of predefined (sensitivity, specificity, positive predictive value) and post-hoc derived cut-offs (overall diagnostic accuracy, sensitivity, specificity, positive predictive value), post-hoc adjustments for multiple comparisons. The following post-hoc adjustment for multiple comparisons was applied: the p-value for the comparison of overall diagnostic accuracy of copeptin after hypertonic saline infusion test compared to the indirect water deprivation test in discriminating partial central diabetes insipidus from primary polydipsia was multiplied by three to account for the two primary superiority tests. The p-values of comparisons of measurements on osmotic stimulation, copeptin release and urinary response were each adjusted according to the Bonferroni-Holm method. All analyses were conducted using the statistical software package R (R Core Team, 2017) 7 using a significance level, α, of 5 %. 4

6 FIGURES Figure S1 Patient Flow Chart Diagram Patient flow diagram according to the evaluated tests CRS = clinical reference standard; DI = diabetes insipidus; PP = primary polydipsia; *inconclusive diagnosis was counted as false diagnosis 5

7 Figure S2 Relation of Plasma Copeptin to Plasma Sodium Levels in Patients with Central Diabetes Insipidus and Primary Polydipsia at the End of the Hypertonic Saline Infusion Test Data points from individual patients with primary polydipsia (= blue triangle), partial central diabetes insipidus (= yellow rhombus), and complete central diabetes insipidus (= red circle) taken at the end of the hypertonic saline infusion test. The relationship of plasma copeptin to plasma sodium concentration is subnormal in central diabetes insipidus and normal or above in primary polydipsia. The orange area represents the normal range obtained from a large group 6

8 (n=91) of healthy adults who underwent the same hypertonic saline infusion protocol 8. The horizontal broken line indicates the pre-defined cut-off of 3% saline stimulated copeptin level of 4.9pmol/l to distinct central diabetes insipidus from primary polydipsia. Figure S3 A Plasma Copeptin Levels after Overnight Fluid Deprivation Copeptin levels (pmol/l) after overnight water deprivation according to final diagnosis 7

9 B ROC Curve for Plasma Copeptin Levels after Overnight Fluid Deprivation ROC curve for plasma copeptin levels after overnight fluid deprivation for discriminating patients with complete central diabetes insipidus from patients with partial central diabetes insipidus or primary polydipsia. 8

10 ROC area under the curve = (95% CI 0.757, 0.914). 95% confidence intervals of sensitivity and specificity are indicated for the predefined cut-off of <2.6pmol/l. Figure S4 Sodium Change as Function of Volume and Duration of 3% Saline Infusion 9

11 TABLE Table S1: Results of the Water Deprivation Test and Hypertonic Saline Infusion Test on Osmotic Stimulation, Copeptin Release and Urinary Response Water deprivation test Hypertonic saline infusion test complete DI (n=36) Plasma sodium, mmol/l 148 (145, 151) Plasma osmolality, mosm/kg 302 (297, 307) Plasma copeptin, pmol/l 1.9 (1.5, 2.7) Urine volume (ml) during WDT 2180 (1429, 2918) Maximal urine osmolality (mosm/l) after WDT Urine osmolality after desmopressin injection (%) 152 (107, 172) 252 (165) central DI PP p value central DI PP p value partial DI (n=23) 145 (143, 148) 295 (292, 301) 3.2 (2.8, 4.1) 885 (579, 1250) 494 (431, 573) 117 (23) (n=82) complete DI (n=36) 141 (140, 143) 153 (150, 155) (283, 291) (302, 316) (3.1, 5.1) (1.6, 2.7) 745 (414, 1078) 653 (552, 755) 34 (5) partial DI (n=23) 152 (150, 155) 311 (303, 318) 3.7 (2.7, 4.8) (n=82) 151 (149, 152) (300, 309) 20.9 (12.7, 27.3) 10

12 Median (IQR) levels of plasma sodium (mmol/l), plasma osmolality (mosm/kg) and plasma copeptin (pmol/l) at the end of the water deprivation test and 3% hypertonic saline infusion test as well as urine output (ml), urine concentration (mosm/l) and reaction to desmopressin injection (%) for the water deprivation test only according to final diagnosis. P-values refer to the comparisons of the corresponding distributions between patients with central diabetes insipidus and patients with primary polydipsia and are adjusted using the Bonferroni-Holm method. DI = diabetes insipidus. 11

13 REFERENCES 1. Timper K, Fenske W, Kuhn F, et al. Diagnostic Accuracy of Copeptin in the Differential Diagnosis of the Polyuria-polydipsia Syndrome: A Prospective Multicenter Study. J Clin Endocrinol Metab 2015;100: Fenske W, Quinkler M, Lorenz D, et al. Copeptin in the differential diagnosis of the polydipsia-polyuria syndrome--revisiting the direct and indirect water deprivation tests. J Clin Endocrinol Metab 2011;96: Morgenthaler NG, Struck J, Alonso C, Bergmann A. Assay for the measurement of copeptin, a stable peptide derived from the precursor of vasopressin. Clin Chem 2006;52: Blaker H. Confidence curves and improved exact confidence intervals for discrete distributions. Canad J Statist 2000;28: DeLong ER, DeLong DM, Clarke-Pearson DL. Comparing the areas under two or more correlated receiver operating characteristic curves: a nonparametric approach. Biometrics 1988;44: Youden WJ. Index for rating diagnostic tests. Cancer 1950;3: R Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria Fenske W, Schnyder I, Koch G, et al. Release and Decay Kinetics of Copeptin versus AVP in Response to Osmotic Alterations in Healthy Volunteers. J Clin Endocrinol Metab 2017;in press. 12