Development of a Clinical Laboratory Supervised System (CLASSY)

Screening for primary hyperparathyroidism (PHPT) in clinic patients: differential diagnosis between PHPT and malignancy-associated hypercalcemia by routine blood tests

Screening for primary hyperparathyroidism (PHPT) by measurement of the serum calcium concentration detects one patient per 500-1000 individuals in Western countries, and one patient per 2500-5000 subjects in Japan. Among clinic patients, however, the presence of many false-positive cases due to malignancy-associated hypercalcemia (MAH) reduces the benefit of such screening. We evaluated a new method of screening for PHPT based on the results of routine blood tests using the hospital information system (HIS) at our hospital. This new method could distinguish PHPT from MAH. This study included 25179 blood samples in which the serum calcium (Ca), albumin (Alb), chloride (Cl) and inorganic phosphate (IP) concentrations had been measured between March, 1994 and February, 1995 at Osaka University Medical Hospital. The HIS was programmed to pick blood samples that satisfied Formula 1 [Ca(mEq/ml) > 0.3 x Alb(g/dl) + 4.1] and Formula 2 ([Cl(mEq/ml)-84] x [10 x Alb-15]/[IP(mg/dl)/3.1] > 400). Of data from 25179 blood samples collected, those from 54 patients satisfied both Formulae 1 and 2. The patients from which these samples were derived from were subject to further analysis: medical records were studied and the intact-parathyroid hormone concentration was measured if necessary. Of these 54 cases, 19 patients (35.2%) were subsequently diagnosed with PHPT, including two, who were newly diagnosed with PHPT by this screening procedure. Although 35 (64.8%) of 54 patients were false-positive, many of them were treated with blood purification therapies in the Department of Pediatrics or the Intensive Care Unit (ICU). On the other hand, there were four false-positive cases (7.4%) caused by MAH. False-negative case in this study was only one patient (5%), whose diagnosis was normocalcemic PHPT. When omitting samples from pediatric patients and those in ICU, this screening procedure for PHPT has the advantage of being able to differentiate this diagnosis from MAH.