PTH and secondary hyperparathyroidism: Other causes of secondary hyperparathyroidism have to be excluded; these include medications known to affect PTH levels (diuretics, lithium, denosumab, bisphosphonates, anticonvulsants, and phosphorus), low vitamin D, chronic kidney disease (estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m2), renal calcium loss (hypercalciuria) and diseases of the gastrointestinal tract known to affect calcium absorption (celiac disease, inflammatory bowel disease, and bariatric surgery) (1-3).