Tertiary hyperparathyroidism is an endocrine and metabolic disorder in which the parathyroid glands, after a prolonged period of stimulation typical of secondary hyperparathyroidism, develop PTH secretion that becomes progressively less dependent on feedback from ionized calcium and active vitamin D. Its characteristic clinical feature is the development of hypercalcemia with persistently elevated PTH in a patient with a history of advanced chronic kidney disease or previous severe secondary hyperparathyroidism, often in the setting of kidney transplantation or, more generally, after partial correction of the uremic determinants. At this stage, the parathyroid response is no longer a useful adaptation but a dysfunction characterized by varying degrees of functional autonomy.
Its clinical impact derives from the fact that hypercalcemia and prolonged PTH elevation can act together on bone, the kidneys and the cardiovascular system. In particular, after kidney transplantation, tertiary hyperparathyroidism may impair the stability of mineral metabolism, promote nephrocalcinosis, worsen graft function and increase fracture risk. In non-transplanted patients with advanced CKD, it may represent progression toward a more autonomous phase that is refractory to conservative measures. Diagnosis therefore requires an approach integrating clinical history, biochemical findings and assessment of target-organ damage.
The epidemiology of tertiary hyperparathyroidism is closely related to the natural history of secondary hyperparathyroidism. The condition typically develops after years of parathyroid stimulation in advanced chronic kidney disease (CKD), when glandular hyperplasia and changes in calcium-sensitive and vitamin D-sensitive receptors make PTH secretion less suppressible. The probability of developing tertiary hyperparathyroidism therefore increases with the duration and severity of CKD-related mineral abnormalities, reaching its greatest clinical relevance in patients with a long history of dialysis or particularly severe and difficult-to-control secondary hyperparathyroidism.
Kidney transplantation represents an important epidemiological setting. Restoration of renal function corrects many components of the mineral disorder and may reduce parathyroid stimulation, but advanced hyperplasia and nodular transformation maintain elevated PTH secretion with persistent hypercalcemia in a proportion of patients. In this setting, tertiary hyperparathyroidism may present as post-transplant hypercalcemia with non-suppressed PTH and clinical consequences that include symptoms of hypercalcemia, deterioration of renal function and abnormalities of calcium-phosphate metabolism.
The main risk factors are related to the history of secondary hyperparathyroidism: very high and persistently elevated PTH levels, prolonged exposure to hyperphosphatemia and calcitriol deficiency, long-standing advanced CKD and marked parathyroid hyperplasia. Inadequate phosphate control and complex management of calcium balance, including prolonged periods of active vitamin D therapy or high calcium load, may also contribute to a trajectory in which the gland becomes progressively less responsive to feedback signals. In transplant recipients, a long dialysis history and severe secondary hyperparathyroidism before transplantation increase the likelihood of persistent post-transplant hypercalcemia.
Clinical vulnerability also depends on comorbidities and organ reserve. Patients with pre-existing osteoporosis, frailty, a history of fractures, malnutrition or reduced muscle mass may develop the skeletal consequences of elevated PTH more rapidly. From a renal perspective, impaired graft function or factors predisposing to nephrocalcinosis amplify the effects of hypercalcemia. From this perspective, the clinical epidemiology of tertiary hyperparathyroidism reflects not only its frequency but also the probability that the disorder will become clinically significant because of its complications.
Overall, tertiary hyperparathyroidism represents the outcome of a prolonged and inadequately controlled biological history of secondary hyperparathyroidism. Its distribution in the population therefore mainly reflects the prevalence of advanced CKD, the duration of dialysis and the trajectory of mineral abnormalities over time, as well as the number of patients undergoing transplantation who subsequently develop persistent hypercalcemia during follow-up.
Under physiological conditions, PTH secretion responds from minute to minute to changes in ionized calcium through the calcium-sensing receptor (CaSR) and is modulated by active vitamin D through the vitamin D receptor. In secondary hyperparathyroidism, chronic stimulation results from an environment in which phosphate, calcitriol and serum calcium converge to maintain elevated PTH as a compensatory response. Tertiary hyperparathyroidism develops when this prolonged stimulation causes structural and functional changes in the parathyroid glands that reduce their dependence on feedback mechanisms.
The key transition is the progression from diffuse hyperplasia to nodular hyperplasia and reduced sensitivity to inhibitory signals. As advanced CKD progresses, phosphate retention and increased fibroblast growth factor 23 (FGF23) reduce calcitriol availability, while fluctuations in serum calcium and chronic stimulation maintain parathyroid secretion. Over time, the glands may reduce their expression of CaSR and the vitamin D receptor, shifting the set point for PTH suppression. Consequently, even when upstream conditions improve, the parathyroid glands continue to produce PTH relatively independently.
Kidney transplantation makes this pathophysiological process particularly evident. Recovery of renal function increases calcitriol production and improves phosphate excretion, reducing the physiological stimulus for PTH secretion. However, if the parathyroid glands are hyperplastic and poorly responsive to feedback, PTH secretion remains elevated and may cause hypercalcemia. Hypercalcemia partly reflects excessive bone resorption and increased renal calcium reabsorption mediated by PTH, producing a mineral balance that may become maladaptive for both bone and kidney.
At the skeletal level, chronically elevated PTH tends to increase bone turnover. In a patient with CKD or after transplantation, bone may already have been compromised by years of mineral abnormalities, so the effects of PTH may result in impaired bone quality, pain, reduced strength and increased fracture risk. In transplant recipients, this risk is further influenced by concomitant factors such as immunosuppressive therapy and rapid changes in mineral metabolism during the post-transplant period.
At the renal level, persistent hypercalcemia may increase the risk of nephrocalcinosis and kidney stones and may contribute to functional deterioration in a vulnerable graft. Phosphate may be low or at the lower end of the reference range after transplantation because of the combination of elevated PTH and restored renal excretion, creating a biochemical profile that differs from uremic secondary hyperparathyroidism. Failure to recognize this pattern may lead to misinterpretation and delay targeted treatment of the cause of hypercalcemia.
The overall pathophysiology of tertiary hyperparathyroidism therefore reflects a biological memory within parathyroid tissue, in which chronic stimulation has remodeled the glands and made PTH secretion relatively autonomous. The clinical consequence is a condition that often requires more definitive strategies, because correction of upstream determinants alone may no longer be sufficient once autonomy has become established.
The clinical manifestations of tertiary hyperparathyroidism are largely attributable to the combined effects of hypercalcemia and elevated PTH, although the presentation may be subtle, especially when hypercalcemia is moderate and chronic. In many patients, the disorder is detected through laboratory testing during follow-up for advanced CKD or kidney transplantation, before overt symptoms develop. When hypercalcemia persists, however, systemic symptoms may emerge and affect quality of life and target-organ risk.
During the clinical history, patients may report fatigue, reduced exercise tolerance, sleep disturbances, irritability and difficulty concentrating. Gastrointestinal symptoms such as nausea, constipation and reduced appetite may occur, especially as serum calcium rises. Polydipsia and polyuria may result from the effect of hypercalcemia on renal concentrating ability. In transplant recipients, these symptoms may be incorrectly attributed to medications or coexisting conditions, making an integrated interpretation of the clinical and biochemical findings essential.
From a musculoskeletal perspective, bone pain, proximal muscle weakness and frailty are common in patients with a long history of mineral abnormalities. The risk of fractures may be increased because of both impaired bone quality and reduced strength, which raises the risk of falls. In some patients, the clinical picture includes chronic pain and reduced functional independence, following a course that cannot be explained by renal function alone and requires specific evaluation of mineral metabolism.
The physical examination may reveal nonspecific signs of deconditioning, reduced proximal muscle strength and bone tenderness. More marked hypercalcemia may produce signs of dehydration or neurocognitive changes. In transplant recipients, the clinical assessment should include careful evaluation of urinary symptoms and medication tolerance, because distinguishing between adverse effects, graft dysfunction and endocrine hypercalcemia is often complex.
In summary, tertiary hyperparathyroidism may initially remain clinically silent but becomes progressively relevant because of its renal and skeletal consequences. Persistent hypercalcemia, systemic symptoms and signs of frailty in the setting of advanced CKD or after transplantation should therefore prompt timely and targeted evaluation.
Tertiary hyperparathyroidism should be suspected when a patient with a history of secondary hyperparathyroidism or advanced CKD develops persistent hypercalcemia associated with non-suppressed or elevated PTH. This combination is the most useful diagnostic clue because normal physiology would require suppression of PTH in the presence of hypercalcemia. If PTH remains elevated, relatively autonomous secretion becomes plausible and warrants a dedicated diagnostic evaluation.
In kidney transplant recipients, suspicion should be particularly high during the first months and years of follow-up when serum calcium is elevated or at the upper end of the reference range together with persistent PTH elevation, especially if the pre-transplant history included very high PTH levels and a long duration of dialysis. In these patients, the disorder may also present with low phosphate, a profile that may be misleading if interpreted according to the pattern of uremic secondary hyperparathyroidism. Polyuria, polydipsia, deterioration of renal function or signs of nephrocalcinosis should strengthen the suspicion that hypercalcemia is contributing to additional renal injury.
The condition should also be suspected when optimized medical management of secondary hyperparathyroidism fails to stabilize the biochemical pattern and signs of autonomy appear, particularly an increase in serum calcium that cannot be attributed to calcium loading or active vitamin D therapy. In non-transplanted patients with advanced CKD, hypercalcemia associated with elevated PTH suggests that chronic stimulation has exceeded its adaptive role and progressed to a more autonomous phase requiring a different strategy.
Suspicion is further increased by the development of skeletal or renal complications, including fragility fractures, persistent bone pain, kidney stones, nephrocalcinosis or otherwise unexplained deterioration of renal function in a transplant recipient. In these settings, evaluation should be prompt and based on a complete biochemical assessment of mineral metabolism, because identifying the condition has direct implications for treatment.
The diagnosis of tertiary hyperparathyroidism requires demonstration of persistent hypercalcemia with elevated or inappropriately non-suppressed PTH in a patient with a history of advanced CKD and previous secondary hyperparathyroidism, often in the setting of kidney transplantation. The central diagnostic principle is physiological consistency: hypercalcemia should reduce PTH secretion, so persistently elevated PTH identifies relatively autonomous secretion. Assessment should always consider serum albumin, possible measurement of ionized calcium and repeated blood tests to confirm persistence of the biochemical pattern.
The initial evaluation includes corrected total serum calcium or ionized calcium, PTH, phosphate, alkaline phosphatase, creatinine with estimated glomerular filtration rate and 25-hydroxyvitamin D. In transplant recipients, it is useful to integrate the course of graft function and assess for possible signs of nephrocalcinosis or kidney stones. Phosphate often helps define the context because it may be low in post-transplant tertiary hyperparathyroidism due to the combined effects of elevated PTH and restored renal function, producing a profile that differs from classic uremic secondary hyperparathyroidism.
Diagnostic assessment of tertiary hyperparathyroidism
Parathyroid imaging is not required to establish the diagnosis because diagnosis is biochemical and contextual. It may, however, become useful for treatment planning, especially when surgery is being considered. Neck ultrasonography and scintigraphy may help localize hyperplastic glands or functioning adenomas, but their role is organizational rather than diagnostic. In transplant recipients, assessment should also include nephrological evaluation because treatment decisions must balance control of hypercalcemia, protection of the graft and skeletal risk.
An important step is distinguishing tertiary hyperparathyroidism from primary hyperparathyroidism and evolving secondary hyperparathyroidism. Primary hyperparathyroidism is typically an autonomous disorder without a history of advanced CKD, whereas in tertiary hyperparathyroidism a history of severe and prolonged secondary hyperparathyroidism is integral to interpretation. Correct diagnosis therefore arises from the combination of longitudinal data rather than from a single measurement.
The classification of tertiary hyperparathyroidism is mainly clinical and pathophysiological and is based on the degree of autonomy and the presence of target-organ consequences. A first distinction concerns the clinical setting: tertiary hyperparathyroidism in a non-transplanted patient with advanced CKD and tertiary hyperparathyroidism in a post-transplant patient. In the first setting, the disorder lies on a continuum with severe and refractory secondary hyperparathyroidism, whereas in transplant recipients it emerges as persistent hyperparathyroidism with hypercalcemia in a metabolic environment profoundly altered by recovery of renal function.
A second classification criterion concerns the biochemical and clinical severity of hypercalcemia. Forms characterized by mild but persistent hypercalcemia may initially cause few symptoms but remain clinically significant because of their effects on the kidneys and the risk of calcification and fractures. Forms associated with more marked hypercalcemia may produce systemic symptoms and increase the risks of dehydration, kidney stones and deterioration of renal function, requiring a more rapid and definitive strategy.
Severity also includes the skeletal profile. Elevated alkaline phosphatase, bone pain, fractures or signs of high bone turnover suggest substantial skeletal involvement and increase the likelihood of complications, including postoperative hypocalcemia due to hungry bone syndrome. Conversely, in some patients a long history of mineral abnormalities may have produced qualitatively fragile bone with clinically relevant manifestations even in the absence of extremely abnormal biomarkers. Individualized assessment is therefore required and cannot be reduced to a single parameter.
A final pragmatic classification criterion is the response to medical treatment. Forms that respond adequately to calcimimetics and correction of mineral metabolism constitute a group distinct from refractory forms, in which advanced hyperplasia and reduced feedback sensitivity make surgery more likely. Classification is therefore functional to therapeutic decision-making and prediction of complications.
Treatment of tertiary hyperparathyroidism has two main objectives: stable correction of hypercalcemia and reduction of the PTH burden to prevent skeletal and renal injury. Therapeutic choice depends on the clinical setting, the severity of hypercalcemia, residual renal or graft function and the presence of complications. Medical management may be appropriate in selected and controllable forms, but a definitive strategy is often required in persistent autonomous disease.
In post-transplant patients, the first step requires a careful review of factors that may increase serum calcium, including calcium supplements and active vitamin D therapy. This is essential because part of the hypercalcemia may be iatrogenic or exacerbated by replacement therapy, and correction of these factors may improve the biochemical pattern. However, when PTH remains elevated and hypercalcemia persists, the disorder cannot be explained solely by calcium loading and should be treated as tertiary hyperparathyroidism.
Calcimimetics are among the main medical options because they increase CaSR sensitivity and may reduce both PTH and serum calcium. In transplant recipients, they are often used to control hypercalcemia and reduce PTH while awaiting a definitive decision or when surgery is contraindicated or postponed. Treatment requires monitoring of serum calcium and attention to gastrointestinal adverse effects and possible hypocalcemia, especially when baseline hypercalcemia is only moderate and skeletal reserve is reduced.
When tertiary hyperparathyroidism is persistent and clinically significant, parathyroidectomy becomes a central option. The indication becomes stronger in the presence of sustained hypercalcemia, renal or skeletal complications, nephrocalcinosis, kidney stones or deterioration of graft function that is at least partly attributable to hypercalcemia. Surgery produces a rapid and stable reduction in PTH and serum calcium but requires careful planning and expert perioperative management, particularly because of the risk of postoperative hypocalcemia and hungry bone syndrome, which is more likely after a long history of high bone turnover.
In non-transplanted patients with advanced CKD, treatment is integrated with the management of CKD-mineral and bone disorder (CKD-MBD). Phosphate and vitamin D control remain relevant, but the development of hypercalcemia with elevated PTH suggests a more autonomous and potentially refractory phase. Calcimimetics and targeted strategies may reduce PTH and serum calcium, but refractoriness and complications may require surgery to reduce target-organ risk and improve quality of life.
In every setting, treatment should include assessment of fracture risk and an integrated approach involving nephrology and, when appropriate, specialists in bone metabolism. The objective is not merely to normalize laboratory values but to achieve stable mineral metabolism over time and reduce clinical events, particularly fractures and renal injury, which represent the true prognostic burden of the disease.
Follow-up is essential in tertiary hyperparathyroidism because the disorder dynamically affects serum calcium, phosphate, renal function and skeletal risk. Monitoring should include corrected total serum calcium or ionized calcium, PTH, phosphate, alkaline phosphatase and assessment of renal function. In transplant recipients, surveillance of graft function and signs of nephrocalcinosis or kidney stones provides additional value because persistent hypercalcemia may contribute to progressive renal injury.
During calcimimetic therapy, follow-up aims to maintain a balance by reducing PTH and serum calcium without shifting the patient toward hypocalcemia or mineral instability. The frequency of testing depends on the treatment phase, with closer monitoring during dose titration and wider intervals once stable control has been achieved. Assessment of vitamin D status remains useful because correction of deficiency may modify PTH dynamics and contribute to stable mineral metabolism, although caution is required in the presence of hypercalcemia.
After parathyroidectomy, immediate follow-up focuses on the risk of hypocalcemia and hungry bone syndrome, with monitoring of calcium, phosphate and magnesium and therapeutic supplementation when required. Support may need to be prolonged in patients with high preoperative bone turnover because bone may act as a sink for calcium and phosphate. Long-term follow-up instead focuses on mineral stability, possible supplementation requirements and the course of renal function in transplant recipients.
Skeletal surveillance is an integral component of monitoring. In patients with a long history of mineral abnormalities, skeletal fragility and fracture risk may persist even after control of PTH and serum calcium. Management should therefore include fall prevention, functional rehabilitation and targeted assessment of bone health according to the individual risk profile. In transplant recipients, immunosuppressive therapy and rapid changes in mineral metabolism require an even more integrated clinical interpretation.
Overall, effective follow-up is designed to maintain long-term stability, reduce fluctuations in biochemical parameters and identify renal and skeletal complications at an early stage, as these are the main determinants of the clinical burden of the disease.
The prognosis of tertiary hyperparathyroidism depends on timely recognition, the severity of hypercalcemia and the extent of cumulative skeletal and renal injury. In post-transplant patients, persistent hypercalcemia may affect graft function and increase the risk of nephrocalcinosis. Prognosis therefore improves when serum calcium is corrected in a stable manner and PTH is reduced to levels compatible with balanced mineral metabolism.
The main complications are renal and skeletal. At the renal level, persistent hypercalcemia may promote kidney stones, nephrocalcinosis and deterioration of renal function, especially in a vulnerable graft. At the skeletal level, prolonged PTH elevation increases bone turnover and may contribute to impaired bone quality and fractures, as well as pain and reduced strength. Even after serum calcium has been normalized, skeletal recovery requires time and may remain incomplete when the history of mineral abnormalities has been prolonged.
Cardiovascular complications occur within the broader context of abnormal mineral metabolism, with a possible contribution to vascular and valvular calcification, especially in patients with advanced CKD. In these patients, tertiary hyperparathyroidism acts as one component of a pro-calcific and inflammatory environment, and prognosis also depends on phosphate control and the overall cardiovascular risk profile.
From a therapeutic perspective, the most important complication after surgery is prolonged hypocalcemia due to hungry bone syndrome, which requires monitoring and often intensive supplementation. The likelihood of hungry bone syndrome increases when preoperative bone turnover is high and the disease has been prolonged, making expert postoperative management necessary. Medical therapy with calcimimetics instead requires careful monitoring to prevent hypocalcemia and mineral instability, using an approach that prioritizes long-term stability over excessively rapid correction.
Overall, tertiary hyperparathyroidism is a potentially high-impact clinical condition because it combines hypercalcemia and parathyroid autonomy in patients who are often medically complex. Prognosis is better when therapeutic decisions are individualized, renal and skeletal complications are prevented and metabolic control is maintained through structured and integrated follow-up.