If the cause of high parathyroid hormone but normal calcium and phosphorus cannot be found, vitamin D test and bone density test can be used to determine the cause of the disease in combination with renal function and ultrasound. 1. Vitamin D test: Vitamin D deficiency, severe renal insufficiency, pregnancy, osteochondrosis and other diseases can lead to a decrease in blood calcium and an increase in blood phosphorus, thus causing an increase in the secretion of parathyroid hormone, which compensates for the normalization of blood calcium and blood phosphorus. Vitamin D can be lowered in all of the above diseases, and the differential diagnosis can be based on vitamin D, renal function, ultrasound, X-ray and other examinations. 2. Bone density examination: patients with primary osteoporosis may have elevated parathyroid hormone due to vitamin D deficiency, which compensates to maintain normal calcium and phosphorus. Ultrasound, CT, dual-energy X-ray and other bone density examination can assist in the diagnosis. When parathyroid hormone is high but calcium and phosphorus are normal, the patient should consult a doctor in time, and after examination and evaluation by the doctor, the cause of the disease should be clarified and targeted treatment should be carried out to avoid delaying the disease.