Parathyroid hormone (PTH) maintains the body’s delicate balance of minerals, particularly calcium and phosphorus. This hormone is closely linked to kidney function, and understanding this relationship is important for overall health. Disruptions in this connection can lead to complications, especially for individuals with kidney conditions.
Understanding Parathyroid Hormone
Parathyroid hormone is produced by the parathyroid glands, four small glands located in the neck, behind the thyroid. These glands detect changes in calcium levels in the blood. When calcium levels drop, PTH is released to restore balance.
PTH works on several parts of the body to regulate calcium and phosphorus. It signals the bones to release calcium into the bloodstream. In the kidneys, PTH reabsorbs calcium, preventing its loss in urine, and promotes phosphorus excretion. PTH also enables the kidneys to produce active vitamin D, which then helps the intestines absorb calcium from food.
How Kidney Disease Affects PTH Regulation
Chronic kidney disease (CKD) significantly impacts the normal regulation of parathyroid hormone, often leading to secondary hyperparathyroidism (SHPT). As kidneys become damaged, their ability to filter and excrete phosphorus decreases. This leads to elevated phosphorus, directly stimulating the parathyroid glands to produce more PTH.
Damaged kidneys also lose their efficiency in converting inactive vitamin D into its active form, calcitriol. This deficiency in active vitamin D impairs the body’s ability to absorb calcium from food, resulting in lower blood calcium levels. Low calcium levels further trigger the parathyroid glands to increase PTH production in an attempt to raise calcium back to normal levels. Sustained PTH overproduction can also enlarge the parathyroid glands.
Health Effects of PTH Imbalance in Kidney Disease
Prolonged high levels of PTH in kidney disease, characteristic of secondary hyperparathyroidism, can lead to serious health complications. One consequence is renal osteodystrophy, a bone disease. In this condition, the continuous pull of calcium from bones by excessive PTH can weaken them, increasing the risk of bone pain and fractures.
Another effect is vascular calcification, where calcium and phosphorus accumulate in blood vessels. This hardening of arteries increases the risk of cardiovascular diseases, a leading cause of complications and mortality in CKD patients. Patients may also experience other symptoms such as persistent itching, muscle weakness, and fatigue, impacting their overall quality of life.
Management of PTH Levels
Managing PTH levels in kidney disease involves a multi-pronged approach, beginning with regular monitoring. Blood tests measure PTH, calcium, phosphorus, and vitamin D levels to assess imbalance. Guidelines from Kidney Disease: Improving Global Outcomes (KDIGO) recommend monitoring PTH levels in CKD patients, especially in stages 3-5. Frequency varies based on disease stage.
Dietary modifications are often a first step, particularly restricting phosphorus intake to help control elevated phosphate levels. Medications include phosphate binders, which reduce phosphorus absorption from food. Activated vitamin D analogs, such as calcitriol or paricalcitol, are also used to suppress PTH secretion and improve calcium and phosphorus balance. In cases where medication and dietary changes are insufficient, calcimimetics like cinacalcet may be prescribed to mimic calcium’s effect on the parathyroid glands, thereby reducing PTH release. For severe cases unresponsive to medical therapy, surgical removal of part or all parathyroid glands (parathyroidectomy) may be considered.