Psychometric Evaluation of the Hypoparathyroidism Symptom Diary: Data from a Prospective Phase 3b/4 Study

To assess the psychometric properties of the disease-specific Hypoparathyroidism Symptom Diary (HypoPT-SD) patient-reported outcome (PRO) tool, which consists of a 7-item symptom subscale, a 4-item impact subscale, a single item for anxiety, and a single item for sadness or depression, using data from the BALANCE randomized, placebo-controlled Phase 3b/4 study (NCT03324880).

Eligible patients had symptomatic hypoparathyroidism (HypoPT) at baseline and were aged 18-85 years (inclusive). Patients received recombinant human parathyroid hormone (1-84) or placebo. The HypoPT-SD was filled in daily; data recorded at baseline and Weeks 4, 12, and 26 (end of treatment [EOT]) were included in this analysis. Inter-item and item-total correlations were used to assess HypoPT-SD structure; Cronbach's coefficient α was used to analyze the internal consistency and reliability, and intraclass correlations were used to measure test-retest reliability. Construct validity was determined using correlational analyses between HypoPT-SD scores and scores from other conceptually similar PRO tools. Ability to detect change was assessed and thresholds for meaningful within-patient change were established.

The psychometric analysis population (N=93) was predominantly female (88.2%) and white (96.8%), with a mean age of 48.5 years. Inter-item correlations ranged from 0.35 to 0.85 at baseline and from 0.49 to 0.93 at EOT. Item-total correlations ranged from 0.57 to 0.83 at baseline and from 0.69 to 0.88 at EOT. Cronbach's α values at baseline were 0.90 (symptom subscale) and 0.88 (impact subscale). Intraclass correlation coefficients for both subscales in stable patients exceeded 0.70. Significant cross-sectional correlations were observed with most of the conceptually linked PRO tools analyzed, and HypoPT-SD scores were responsive to change. Potential changes of 1.5 (symptom subscale) and 0.8 (impact subscale) were determined as meaningful change thresholds for within-patient improvements.

The HypoPT-SD is a reliable measure of key symptoms and impacts of HypoPT.