Acute pancreatitis, hypercalcemia, and kidney stones: True incidence or unveiled prevalence?

Abstract

Recent study reported an association between hypercalcemia and nephrolithiasis in acute pancreatitis and proposed a striking rate of de novo stone formation during a 7-day hospitalization. Their work is valuable because it draws attention to the endocrine-metabolic dimension of acute pancreatic injury and to a potentially vulnerable subgroup of patients. However, the reported endpoint raises major biological and methodological concerns. Lithogenesis is a multistep process requiring urinary supersaturation, nucleation, aggregation, epithelial interaction, and retention; clinically meaningful stones generally evolve over weeks to months, not days. Moreover, although contrast-enhanced computed tomography was available at baseline and day 7, renal stone assessment relied on serial ultrasonography and on echogenic foci > 2 mm with posterior acoustic shadowing, a definition closer to microlithiasis than to established calculi. The absence of baseline non-contrast computed tomography analysis and 24-hour urinary biochemical profiling further weakens the inference of true incident nephrolithiasis. We therefore argue that the findings are more plausibly explained by the acute unmasking of prevalent, previously unrecognized microlithiasis under inflammatory-metabolic stress rather than by genuine de novo stone formation.

Key Words: Acute pancreatitis; Hypercalcemia; Nephrolithiasis; Microlithiasis; Parathyroid hormone; Ultrasonography; Computed tomography; Incidence; Prevalence

Core Tip: The association between hypercalcemia and renal stone detection in acute pancreatitis is clinically important, but a 7-day timeline is biologically inconsistent with established lithogenesis. Serial ultrasonography during acute illness is more likely to reveal pre-existing silent microlithiasis or transient crystal aggregates than true de novo nephrolithiasis. Distinguishing unveiled prevalence from true incidence is essential because it changes both the interpretation of the study and subsequent patient management.

INTRODUCTION

Acute pancreatitis (AP) is a complex inflammatory disorder with a clinical spectrum ranging from mild, self-limited disease to severe systemic illness accompanied by organ dysfunction and major metabolic derangements[1-4]. Disturbances in calcium homeostasis are well recognized in this setting. In routine clinical practice, hypocalcemia is the expected biochemical pattern and is classically attributed to calcium sequestration within areas of fat necrosis and peripancreatic saponification[1-3]. By contrast, hypercalcemia is distinctly less common and usually raises concern for an underlying endocrine or metabolic disorder, particularly primary hyperparathyroidism (PHPT)[5-8].

Recent work has renewed interest in the possibility that systemic inflammation itself may perturb calcium-regulating pathways. Interleukin-6 and related mediators can intersect with parathyroid hormone (PTH), PTH-related peptide, calcium-sensing receptor signaling, and bone-mineral turnover, thereby creating a transient inflammatory-endocrine phenotype during acute illness[9-13]. These observations are clinically relevant because they challenge the simplistic framework in which hypocalcemia is viewed only as a consequence of AP, whereas hypercalcemia is considered solely a pre-existing cause.

Nephrolithiasis, however, is fundamentally a time-dependent biological process involving supersaturation, nucleation, crystal aggregation, epithelial interaction, and retention[14-18]. Although acute metabolic stress may favor crystalluria, the formation of clinically meaningful stones generally evolves over weeks to months rather than days[19-23]. We therefore read with great interest the study by Wang et al[24], which explored the correlation between hypercalcemia, calcium-regulating hormones, and renal stone formation in AP. The authors should be commended for highlighting a metabolically complex subgroup. Nevertheless, their central claim - a de novo nephrolithiasis incidence of 16.8% within 7 days, with a discordant 35% figure in the core tip - raises substantial biological and methodological concerns.

CALCIUM HOMEOSTASIS IN AP

Calcium disturbances have long occupied a central place in the metabolic profile of AP. Hypocalcemia is far more common than hypercalcemia and has historically been interpreted as a marker of disease severity, largely because of calcium sequestration within areas of fat necrosis and saponification[1-4]. In this classical model, low serum calcium is not merely a laboratory abnormality but a biochemical reflection of tissue injury and systemic inflammation.

Hypercalcemia, by contrast, is unusual in AP and more often suggests that an independent endocrine disorder preceded the pancreatic event. The best-recognized example is PHPT, in which longstanding hypercalcemia may contribute to pancreatitis through calcium-mediated acinar injury, ductal effects, and premature enzyme activation[5,6,25-27]. Hypercalcemia can also accompany malignant disease and other rare metabolic contexts, again usually as a predisposing factor rather than a simple consequence of pancreatitis[7,8,28]. Accordingly, in patients with recurrent or otherwise unexplained AP, PHPT and other endocrine causes should remain prominent in the differential diagnosis.

At the same time, systemic inflammation may itself perturb calcium-regulating pathways. Acute illness can alter plasma volume status, renal handling of calcium, hormone secretion, and protein binding. Experimental and translational data suggest that inflammatory cytokines, especially interleukin-6, may interact with PTH and PTH-related peptide pathways, while calcium-sensing receptor signaling can amplify inflammatory responses[9,10,12,13,29]. More recent multicenter evidence also supports the clinical importance of hypercalcemia as a modifier of AP severity[30]. Thus, hypercalcemia observed during AP may occasionally represent a reversible inflammatory-endocrine response rather than only a chronic pre-existing endocrine disorder.

THE HYPERCALCEMIA PARADOX IN AP

The first point of discussion in the Wang et al’s study[24] is the reported incidence of hypercalcemia (28.6%). This finding is intriguing because AP is classically associated with hypocalcemia, not hypercalcemia[1,3,4]. While hypercalcemic pancreatitis is a recognized entity, it is most often attributed to PHPT or related disorders that act as the cause of pancreatitis rather than as its consequence[5,6,25-27]. Wang et al[24] excluded patients with PHPT, thereby implying that the observed hypercalcemia arose during the acute inflammatory state itself. Their finding that PTH peaked on day 3 is compatible with an inflammation-linked endocrine perturbation, but the mechanistic interpretation remains incomplete because ionized calcium, cytokine profiles, PTH-related peptide, and formal volume-status metrics were not serially characterized. In this setting, causal hypercalcemia, concentration-related hypercalcemia, and reactive inflammatory-endocrine dysregulation cannot be cleanly separated[10-13,29]. This distinction matters because the downstream inference is not limited to transient biochemical fluctuation; it extends to the far stronger claim of rapid de novo stone formation.

PATHOPHYSIOLOGY OF NEPHROLITHIASIS

Nephrolithiasis is a multistep physicochemical and biological process rather than a single event. At its core lies urinary supersaturation, which provides the thermodynamic basis for crystal formation. Yet supersaturation alone is insufficient. Crystals must nucleate, grow, aggregate, interact with the tubular or papillary environment, avoid washout, and progressively enlarge before they become clinically meaningful calculi[14-18].

Urinary promoters and inhibitors jointly determine whether this process will proceed. Urinary calcium, oxalate, uric acid, sodium, pH, and volume interact with inhibitors such as citrate, magnesium, pyrophosphate, and macromolecular modulators of crystal growth[19,31-34]. Consequently, serum hypercalcemia alone cannot be equated with stone formation unless the urinary lithogenic milieu is also demonstrated. Crystal retention and tissue interaction are equally central. Epithelial injury, papillary microenvironment, Randall plaque biology, inflammatory signaling, and heritable susceptibility all influence whether transient crystals remain fleeting or evolve into stable stones[35-39]. These cumulative events reinforce a simple point: Nephrolithiasis is the product of biological time, not merely a momentary biochemical insult.

A SEVEN-DAY LITHOGENESIS? THE QUESTION OF BIOLOGICAL PLAUSIBILITY

The most difficult aspect of the Wang et al’s study[24] is the interpretation of renal stone detection as true de novo nephrolithiasis during a 7-day hospitalization. A sudden increase in urinary calcium excretion may certainly generate crystalluria, especially in a dehydrated or catabolic patient. However, progression from free crystals to organized matrix-based calculi detectable by ultrasonography is far more gradual and usually requires weeks to months, and often substantially longer[20-23,31].

The metabolic investigation reported by Wang et al[24] also lacked critical elements required for a lithogenic-risk assessment. Guideline-based evaluation of stone disease requires 24-hour urinary biochemical analysis to quantify lithogenic promoters, litholytic inhibitors, urinary pH, and total volume[32-34,40,41]. Even if AP transiently generates a high-risk urinary profile, such as low urine volume, hypocitraturia, or inflammatory crystal aggregation, the absence of formal urinary phenotyping precludes a confident conclusion that serum hypercalcemia alone produced new stones in only 7 days[42-44].

ACUTE METABOLIC STRESS, CRYSTALLURIA, AND MICROLITHIASIS

Acute illnesses such as dehydration, systemic inflammation, and severe metabolic stress can transiently increase urinary supersaturation. Reduced urine volume, altered acid-base status, hypercalciuria, and diminished urinary inhibitors may create a crystal-prone environment over a short time frame[19,32-34,42]. AP, therefore, may plausibly favor crystalluria or microscopic crystal aggregation during the acute phase. Key acute factors that may transiently favor crystalluria without proving de novo stone formation are summarized in Table 1. Transient crystalluria or microlithiasis, however, is not equivalent to true incident stone disease[16,21,39]. Small unstable deposits or sludge-like echogenic material may appear rapidly and may also regress once hydration status, inflammatory burden, and calcium balance normalize. This distinction is clinically important because a transient crystal signal and an established nephrolithiasis phenotype are not interchangeable endpoints. In our view, the Wang et al[24] findings are much more compatible with acute unmasking of prevalent but previously unrecognized microlithiasis than with rapid de novo lithogenesis. The conceptual distinction between true incident nephrolithiasis and acute unveiling of prevalent microlithiasis is summarized in Table 2.

Table 1 Acute factors during pancreatitis that may favor crystalluria without proving de novo stone formation.

Metabolic factor	Likely acute effect	Interpretive implication
Intravascular volume depletion	Urine becomes concentrated, and supersaturation rises	Transient crystalluria may increase without establishing a new stable stone
Hypocitraturia or reduced inhibitors	Protective buffering against crystal aggregation decreases	Aggregation may be facilitated, but organized calculi still require time and retention
Transient hypercalcemia	Possible short-term increase in urinary calcium excretion if sustained	Serum calcium alone is insufficient evidence for stone causation without urine data
Inflammatory epithelial stress	Crystal adhesion and urothelial interaction may be altered	Acute illness may unmask a pre-existing crystal burden rather than generate a new calculus
Serial ultrasonography during recovery	Visibility of tiny echogenic foci may change with operator, body habitus, and acoustic windows	Apparent incidence may reflect detection bias instead of true lithogenesis

Table 2 Distinguishing true incident nephrolithiasis from unveiled prevalent microlithiasis in acute pancreatitis.

Domain	True incident nephrolithiasis	Unveiled prevalent microlithiasis
Biological premise	New crystal nucleation, aggregation, retention, and growth produce a genuinely new stone	Previously silent crystals or microliths become detectable during acute evaluation
Expected time course	Usually, weeks to months before a clinically meaningful calculus becomes evident	Detection may shift from hours to days without implying new stone formation
Baseline imaging expectation	No renal deposit should be present on high-quality baseline computed tomography	Small pre-existing deposits may be missed on ultrasound, yet still be present at baseline
Urinary evidence needed	Persistent lithogenic profile on 24-hour urine supports causal inference	Acute metabolic disturbance may transiently increase visibility without proving chronic stone disease
Short-term behavior	Lesion persists or enlarges on follow-up imaging	Focus may regress after hydration and recovery from inflammatory-metabolic stress
Clinical implication	Long-term stone prevention and metabolic evaluation are usually warranted	Repeat post-recovery assessment is needed before labeling chronic nephrolithiasis

IMAGING PITFALLS AND ENDPOINT MISCLASSIFICATION

Imaging methodology is central to the interpretation of renal stone outcomes. Although Wang et al[24] reported contrast-enhanced computed tomography (CT) at admission and again on day 7, stone detection was based on serial renal ultrasonography rather than on CT analysis. This choice is methodologically consequential because ultrasonography is substantially less reliable than CT for identifying very small calculi and for distinguishing true stones from echogenic debris[45-49]. Our proposed interpretive framework is shown in Figure 1.

Figure 1 Acute pancreatitis may generate systemic inflammation and transient metabolic perturbations, including changes in serum calcium, parathyroid hormone dynamics, urine volume, and urinary inhibitors of crystallization. When serial ultrasonography is used without computed tomography-based renal endpoint confirmation, these acute changes can increase the visibility of pre-existing silent microlithiasis or transient crystal aggregates. Under this framework, apparent short-term “de novo nephrolithiasis” may represent an imaging-mediated unveiling of prevalent microlithiasis rather than biologically plausible new stone formation. PTH: Parathyroid hormone; CT: Computed tomography.

Ultrasonography is highly operator dependent and has reduced sensitivity for small stones, particularly those smaller than 5 mm[50-54]. In addition, ultrasound may overestimate the size of small stones and may be influenced by body habitus, hydration, acoustic window quality, and repeat scanning conditions[47,54,55]. Thus, a small echogenic focus visible on day 7 but not on day 0 does not necessarily represent a newly formed calculus; it may simply reflect improved visibility of pre-existing microlithiasis or sludge-like material.

The endpoint definition further magnifies this problem. Echogenic foci greater than 2 mm with posterior acoustic shadowing are much closer to a sonographic microlithiasis definition than to a CT-based definition of clinically established stone disease[45-47,50,55]. If CT images were not interrogated for baseline renal stone burden, then the study design could easily convert missed prevalent microlithiasis into apparent incident nephrolithiasis. In other words, serial ultrasound in an acutely ill population may create the illusion of incidence when the more plausible explanation is detection bias.

CLINICAL IMPLICATIONS AND FUTURE DIRECTIONS

This distinction is not merely semantic. If the detected lesions were transient crystal aggregates or inflammatory sludge, management should focus primarily on correcting the acute metabolic disturbance, ensuring adequate hydration, and reassessing after recovery. By contrast, if the lesions reflect pre-existing nephrolithiasis or persistent microlithiasis, patients may require formal metabolic work-up, long-term urological or nephrological surveillance, and recurrence-prevention strategies[32,34,41,42,56]. Misclassifying prevalence as incidence can therefore distort risk perception, trigger unnecessary imaging, and lead to avoidable referrals or interventions. Future studies should use standardized non-contrast CT-based renal endpoints, report stone size and location explicitly, and incorporate delayed 24-hour urinary biochemical profiling after clinical stabilization[44-47,55]. Serial measurements of ionized calcium, PTH, inflammatory mediators, and urinary citrate and calcium would improve mechanistic clarity. Such designs would help distinguish causal endocrine disease, reactive inflammatory-endocrine dysregulation, transient crystal phenomena, and true persistent nephrolithiasis.

Broader metabolic follow-up may also be informative. Pancreatitis is increasingly recognized as a disorder with systemic skeletal and mineral consequences beyond the acute episode, especially in chronic or recurrent disease[57-60]. This broader perspective strengthens the case for not overinterpreting a short in-hospital imaging signal as definitive evidence of rapid de novo lithogenesis. Rather, AP should be viewed as an inflammatory-metabolic stress test that may unmask previously silent abnormalities in calcium handling, bone-mineral metabolism, and urinary crystal risk.

CONCLUSION

Wang et al[24] have highlighted a clinically important high-risk subgroup and deserve credit for drawing attention to the endocrine-metabolic dimension of AP. Nevertheless, their protocol did not demonstrate that stones were created during 7 days of hospitalization; it demonstrated that very small renal echogenic foci were detected during a period of acute inflammatory and metabolic stress. Given the known biology of lithogenesis, the absence of urinary metabolic profiling, and the methodological limitations of ultrasound-based stone detection despite available CT imaging, the reported endpoint is much more plausibly interpreted as the unveiling of pre-existing, asymptomatic microlithiasis than as true incident nephrolithiasis. Distinguishing unveiled prevalence from true incidence is essential because it determines both the scientific interpretation of the study and the clinical management that follows.