Which of the following biochemical change is seen in primary hyperparathyroidism?

In primary hyperparathyroidism the hallmark feature is hypercalcemia, the urinary calcium excretion may be high or normal but it is usually low for the degree of hypercalcemia and the serum phosphate is low. Functions of parathyroid hormone: Parathyroid hormone acts on bone and causes to increase bone resorption and mobilise calcium. It also increases re absorption of calcium in the distal tubules of kidney. It increases phosphate excretion in the urine and thereby depress plasma phosphate levels. It increases the formation of 1,25 dihydroxycholecalciferol which increases calcium absorption from the intestine. Ref: Fitzgerald P.A. (2013). Chapter 26. Endocrine Disorders. In M.A. Papadakis, S.J. McPhee, M.W. Rabow, T.G. Berger (Eds), CURRENT Medical Diagnosis & Treatment 2014. Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 21. Hormonal Control of Calcium & Phosphate Metabolism & the Physiology of Bone. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.