Osteocalcin and urinary hydroxyproline/creatinine ratio in the differential diagnosis of primary hyperparathyroidism and hypercalcaemia of malignancy

Osteocalcin (serum bone-Gla protein, sBGP), serum alkaline phosphatase (sAP) and urinary hydroxyproline/creatinine ratio (uOH-Prol/creatinine) have been measured in 21 patients with primary hyperparathyroidism (PHPT) and in nine patients with hypercalcaemia of malignancy (HM). A positive linear correlation between sBGP and uOH-Prol/creatinine ratio (y = 0.023 + 0.0025x; r = 0.705; p less than 0.01) and between sBGP and sAP (y = 35.6 + 2.14x; r = 0.430, p less than 0.05), have been observed in the PHPT patients. No correlation was found in the HM patients. PHPT patients have been grouped according to their uOH-Prol/creatinine ratio (group A: uOH-Prol/creatinine greater than 0.034; group B: uOH-Prol/creatinine less than or equal to 0.034). Group A presented sBGP higher than the control group (11.06 +/- 5.7 vs. 4.2 +/- 1.2 ng/ml; p less than 0.001) (mean +/- SD). Group B presented sBGP similar to the control group (4.4 +/- 1.96 ng/ml) (mean +/- SD). Group A presented serum calcium (sCa) higher than group B (3.11 +/- 0.28 vs. 2.78 +/- 0.09 mmol/l; p less than 0.01) (mean +/- SD). In HM patients uOH-Prol/creatinine ratio was elevated as compared with the control group (0.074 +/- 0.036 vs. 0.024 +/- 0.004; p less than 0.001) (mean +/- SD), but sBGP was normal or low (range: indetectable-5.1 ng/ml). The simultaneous estimations of sBGP and uOH-Prol/creatinine ratio improve the differential diagnosis between these two forms of hypercalcaemia: high uOH-Prol/creatinine ratio with concomitant high sBGP point to the presence of PHPT. Elevated uOH-Prol/creatinine ratio with normal or low sBGP suggest the existence of HM.(ABSTRACT TRUNCATED AT 250 WORDS)