title: Calculating an individual maxPTH to aid diagnosis of normocalemic primary hyperparathyroidism.
abstract: BACKGROUND
  We aimed to validate a nomogram for diagnosing primary hyperparathyroidism (PHP), particularly when normocalcemic PHP and vitamin D (VitD25) deficiency coexist.
  
  
  METHODS
  The nomogram calculates maximal upper limit of normal PTH unique for each person by maxPTH = 120 - [6*calcium] - [½*VitD25] + [¼*age]. PHP is suspected when serum PTH exceeds maxPTH. Normocalcemic PHP (NCPHP) was defined as always normal serum calcium (8.5-10.5 mg/dL) with PTH >60 pg/mL preoperatively and VitD25 deficiency as <31 ng/mL.
  
  
  RESULTS
  A total of 477 patients had operatively and histologically proven PHP. Overall and including those with classical presentation (high serum levels of calcium and PTH), the nomogram predicted PHP in 97% patients. A total of 66 had NCPHP: 47 with low VitD25 levels (20 ± 0.4 ng/mL) made initial PHP diagnosis challenging; 19 had normal VitD25 status. Although the level of serum calcium concentrations were equivalent in these 2 groups (10.1 ± 0.4 mg/dL), PTH was greater in patients with concurrent VitD25 deficiency (129 vs 97 pg/mL, P = .04). However, when used to calculate maxPTH, the nomogram predicted PHP correctly in all 66 NCPHP patients (100%).
  
  
  CONCLUSIONS
  The maxPTH nomogram functions as expected to classify patients with PHP and may aid in the diagnosis of NCPHP regardless of vitamin D status and repletion, reassuring primary providers and surgeons alike to embark on appropriate and timely PHP management.
authors.affiliation: Department of Endocrine Surgery, Endocrinology and Metabolism Institute, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Judy
authors.initials: J
authors.lastname: Jin
authors.forename: Jamie
authors.initials: J
authors.lastname: Mitchell
authors.forename: Joyce
authors.initials: J
authors.lastname: Shin
authors.forename: Eren
authors.initials: E
authors.lastname: Berber
authors.forename: Allan E
authors.initials: AE
authors.lastname: Siperstein
authors.forename: Mira
authors.initials: M
authors.lastname: Milas
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000097:blood*; D002648:Child; D006801:Humans; D049950:Hyperparathyroidism, Primary / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D008875:Middle Aged; D049451:Nomograms; D010281:Parathyroid Hormone / Q000097:blood*; D014807:Vitamin D / Q000097:blood; D014808:Vitamin D Deficiency / Q000150:complications; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; D002118:Calcium