What are some considerations to make when managing patients with recurrent nephrolithiasis who are found to have nephrocalcinosis on imaging?

Nephrocalcinosis is generally defined as calcification of the renal parenchyma, especially the medulla and papillary tips, as opposed to nephrolithiasis which refers to calcification in the urinary space. The two often coexist.

Nephrocalcinosis, and its accompanying nephrolithiasis, are typically predominantly calcium phosphate, usually some mixture of hydroxyapatite and brushite. Stones of this composition generally require relatively alkaline urine to form; urine pH is typically in the 6.3-6.5 range.

My differential diagnosis of nephrocalcinosis includes primary hyperparathyroidism, distal renal tubular acidosis, and medullary sponge kidneys. Since HPT is surgically correctable, I definitely screen for that. Because normocalcemic primary hyperparathyroidism exists, I am looking for an imbalance among parathyroid hormone, serum calcium, serum phosphorus, and vitamin D levels. if present, I do parathyroid imaging and consult an endocrine surgeon.

I screen for distal RTA with a urinary acidification test. If positive, I typically treat the metabolic acidosis with potassium citrate to avoid osteomalacia.

Rarely, I will try to correct the urine pH to approximately 6.0 with ammonium chloride, depending on the results of the urinary acidification testing. There is minimal research to support this strategy, and there is a risk of worsening osteopenia/porosis.

Stephen B. Erickson, MD

I basically agree with Dr. @Dr. First Last except I do not correct the urine pH with ammonium chloride as I do not believe it is helpful and don’t want to increase the acid load.