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

Serum calcium (S-Ca), the forgotten test: preliminary results of an appropriateness strategy to detect primary hyperparathyroidism (pHPT)

BACKGROUND

With the introduction of automated calcium measurements with multichannel continuous-flow analyzers in the 1970s, primary hyperparathyroidism (pHPT), the silent disease, began to be detected. Years later, with the first appearance of random access analyzers, laboratory tests were requested if the patient had clinical symptoms and pHPT was again overlooked. In this current scenario, serum calcium (s-Ca) is at risk of becoming a forgotten test. In consensus with endocrinologists and general practitioners (GPs), we implemented a strategy to detect asymptomatic pHPT patients.

METHODS

During a 9 month period, the Laboratory Information System automatically added s-Ca to every sample of blood from primary care patients older than 45 years, without a s-Ca request in the previous three years. If hypercalcemia was detected (albumin-corrected s-Ca > 2.6 mmol/L), phosphate, 25-hydroxy vitamin D and parathyroid hormone (PTH) were automatically processed in the same sample. We reviewed the medical record of every patient with hypercalcemia.

RESULTS

S-Ca was automatically added to 14,461 samples, with 79 hypercalcemia results. 14 hypercalcemia results with PTH levels in the reference range were clinically justified by causes other than pHPT. Of the remaining 65 patients, 41 were referred for evaluation by endocrinology. 34 resulted in a diagnosis of pHPT and 7 are currently in study. 24 patients were not followed by GPs to find out the primary cause of hypercalcemia. After a phone call from the laboratory, they are also currently being studied for hypercalcemia. Each case represented a cost of 110.4 US dollars.

CONCLUSION

Our proposed opportunistic screening to discover pHPT seems cost-effective.

Non-malignant causes of hypercalcemia in cancer patients: a frequent and neglected occurrence

PURPOSE

Hypercalcemia is a frequent finding in cancer patients and can be observed in any type of cancer. The physician in charge of cancer patients often ignores non-malignant causes of hypercalcemia. Our objective was to review the causes of hypercalcemia in a large series of cancer patients.

METHODS

We have retrospectively studied in a Cancer Centre all consecutive hypercalcemic (Ca> 10.5 mg/dl) patients over an 8-year period. Of 699 evaluated patients, 642 were analyzed after exclusion of patients whose hypercalcemia resolved after rehydration or who had a normal Ca level after correction for protein concentrations. Clinical information was gathered on the type of cancer, its histology, whether the disease was active or in complete remission, and on the presence of bone metastases. Biochemical data included serum Ca, P(i), proteins in all patients, PTH in most patients, and PTHrP, 25OH-Vitamin D, 1,25(OH)(2)-Vitamin D, TSH, and T4 in selected cases.

RESULTS

By order of decreasing frequency, the main causes of hypercalcemia were cancer (69.0 %), primary hyperparathyroidism (24.6 %), hyperthyroidism (2.2 %), milk alkali syndrome (0.9 %), and sarcoidosis (0.45 %). In cancer-related causes, bone metastases accounted for 53.0 % of the cases, humoral hypercalcemia of malignancy (HHM) for 35.3 % while there were 11.7 % of cases apparently due to both HHM and bone metastases. Hypercalcemia was not due to cancer in 97 % (84/87) of the patients who were in complete remission. Even in patients with active neoplastic disease, the number of patients whose hypercalcemia was not due to cancer remained clinically relevant (115/555 = 20.5 %). In the 158 patients with primary hyperparathyroidism, 92 patients were in complete remission and 66 patients had active neoplastic disease.

CONCLUSIONS

In this large series of hypercalcemia in cancer patients, the cause was not due to cancer in almost one third of the cases. Most patients considered to be in complete remission had hypercalcemia due to a benign condition. In that perspective, serum PTH determination is essential in the approach of hypercalcemic cancer patients since primary hyperparathyroidism is by far the first non-malignant cause of hypercalcemia.

Laboratory screening for hyperparathyroidism

INTRODUCTION

The clinical syndrome produced by excess parathyroid hormone (PTH) is referred to as hyperparathyroidism (HPT). Autonomous growth of PTH producing cells is defined as primary hyperparathyroidism (pHPT). In its classic form pHPT is characterized by painful bones, kidney stones, abdominal groans, psychic moans, fatigue overtones and hypercalcemia. Chronic stimulation of the parathyroid glands secondary to low circulating calcium level results in secondary hyperparathyroidism (sHPT). Tertiary hyperparathyroidism (tHPT) results from prolonged secondary hyperparathyroidism when the glands take on an autonomous function manifested by hypercalcemia and high PTH levels despite resolution of the original stimulus.

REVIEW

The paper reviews the physiologic regulation of PTH secretion and types and forms of HPT. Calcium homeostasis is discussed, emphasizing interactions of PTH, PO4 and vitamin D that can lead to HPT. In addition, the paper reviews the contribution of serum calcium, chloride, phosphorus and PTH levels to the diagnosis of HPT, the role of urinary calcium in the diagnosis of familial benign hypocalciuric hypercalcemia (FBHH), and the role of alkaline phosphatase and bone mass measurements as markers of severity of hyperparathyroid bone disease.

CONCLUSIONS

It is concluded that the diagnosis of hyperparathyroidism can be made with a very high confidence rate by documenting an increased serum PTH level with an increased ionized or total calcium level in pHPT, increased serum PTH level with low or normal calcium level and an underlying renal failure or vitamin D deficiency in sHPT. Early management of HPT is important because many of the nonspecific complains, or classic symptoms, or metabolic conditions often improve after proper control of hyperparathyroidism.