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

Abstract

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<0.01) and between sBGP and sAP (y=35.6+2.14x; r=0.430, p<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>0.034; group B: uOH-Prol/creatinine≥0.034). Group A presented sBGP higher than the control group (11.06±5.7 vs. 4.2±1.2 ng/ml; p<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<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<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. Hypercalcaemia with normal uOH-Prol/creatinine ratio independent of sBGP indicates the absence of bone involvement in PHPT patients.

Key words:

• BGP
• bone Gla protein