Parathyroid hormone and calcium nomogram. Relationship between serum intact parathyroid hormone (PTH) and serum calcium levels in patients with hypoparathyroidism, pseudohypoparathyroidism, nonparathyroid hypercalcemia, primary hyperparathyroidism (HPT), and secondary hyperparathyroidism. (Reproduced with permission from GJ Strewler, MD.) Note: A multivariate model that adds clinical and demographic information may perform better than the nomogram alone. (See O'Neill SS et al. Multivariate analysis of clinical, demographic, and laboratory data for classification of disorders of calcium homeostasis. Am J Clin Pathol. 2011 Jan;135(1):100-7. [PMID: 21173131])