Approximately one in 11 persons in the United States has been affected by kidney stones; among those who have experienced a kidney stone, the likelihood of recurrence is high, with up to 50% developing a recurrent stone within 10 years of the first episode. Hyperparathyroidism (PHPT) is evident in approximately 3% to 5% of patients with kidney stones and screening for PHPT is a strategy aimed at reducing the recurrence rate. Patients with kidney stones and PHPT present with hypercalcemia and hypercalciuria, raising the risk for stones by increasing urine supersaturation for calcium oxalate or phosphate.
Guidelines from the American Urological Association and the European Association of Urology call for measurement of serum calcium in patients with kidney stones, followed by the serum parathyroid level (PTH) if there is clinical suspicion for PHPT. It is unknown whether patients with kidney stones receive those recommended screenings in clinical practice. Results of a previous study suggested that fewer than one in four veterans with persistent hypercalcemia treated in the Veterans Health Administration (VHA) were screened for PHPT.
Calyani Ganesan, MD, MS, and colleagues conducted a cohort study to examine the prevalence of PTH testing in veterans with kidney stones and hypercalcemia. The researchers also sought to identify the demographic, geographic, and clinical characteristics of veterans who were more or less likely to receive PTH testing. The study was designed to test the hypothesis that the frequency of PTH testing remains low despite current clinical practice guidelines and that a wide variation in screening practices is not adequately explained by patient-specific or facility-level factors. Results of the study were reported online in JAMA Surgery [doi:10.1001/jamasurg.2020.2423].
The study utilized VHA health records to identify patients with kidney stones and hypercalcemia who received care in one of the 130 VHA facilities across the United States from January 1, 2008, through December 31, 2013. Patients with kidney stones were those with one or more inpatient International Classification of Diseases, Ninth Revision (ICD-9) codes for kidney or ureteral stones, two or more outpatient ICD-9 codes for kidney or ureteral stones, or one or more Current Procedural Terminology codes for kidney or ureteral stone procedures within 1 year. Exclusion criteria included previous screening for PHPT, defined as those with a PTH level measurement between 6 and 30 months prior to the index stone diagnosis.
Data collection occurred from January 1, 2006, to December 31, 2014. Data analysis occurred from June 1, 2009, to January 31, 2020. The primary outcomes of interest were the proportion of patients with a serum PTH level measurement and the proportion of patients with biochemical evidence of PHPT who underwent parathyroidectomy.
A total of 157,539 unique veterans were diagnosed with kidney stones during the study period. Of those, 139,115 had a serum calcium determination within 6 months of their index stone diagnosis, and 7381 had been previously screened with a serum PTH level measurement and were excluded. Following application of exclusion criteria, the final cohort comprised 7561 patients with kidney stones and measured hypercalcemia (n=3938) or albumin-corrected hypercalcemia (n=3623). Mean age of the final cohort was 64.3 years, 94.4% (n=7139) were men, 5.6% (n=422) were women, and 75.0% (n=5673) were white. Patients with hypercalcemia compared with those with normocalcemia (n=124,173) were more likely to have diabetes (39.8% vs 29.5%), impaired kidney function, defined as estimated glomerular filtration rate <45 mL/min/1.73 m2 (36.1% vs 15.1%), osteoporosis (4.4% vs 2.1%), and fractures (7.1% vs 4.2%).
Of the 7561 patients with kidney stones and hypercalcemia, 24.8% (n=1873) completed a serum PTH level measurement around the time of the initial stone diagnosis. In the 3938 patients with measured hypercalcemia, 34.8% (n=1369) completed a serum PHT level measurement; only 13.09% (n=504/3623) of the patients with albumin-corrected hypercalcemia did so. Of the 1873 veterans with PTH testing, 38.3% (n=717) had an elevated PTH level consistent with biochemical PHPT.
Results of multivariable logistic regression models demonstrated that the odds of PTH testing in patients with kidney stones and hypercalcemia were lower with older age (odds ratio [OR], 0.95 per decade; 95% confidence interval [CI], 0.90-1.00) and among patients with a history of metastatic cancer (OR, 0.63; 95% CI, 0.49-0.81). Patients with albumin-corrected hypercalcemia were less likely to complete PTH testing compared with patients with measured hypercalcemia (OR, 0.32; 95% CI, 0.28-0.37).
The odds of PTH testing were higher for patients who visited either a nephrologist or a urologist (OR, 1.56; 95% CI, 1.35-1.81), and much higher for those who visited both a nephrologist and a urologist (OR, 6.57; 95% CI, 5.33-8.10) compared with patients who did not visit a stone specialty clinic during the observation period.
Across the 130 VHA facilities in the United States, the prevalence of PHT testing among the veterans with kidney stones varied between 4.0% and 57.0%. The study researchers examined the composite complexity score assigned to each facility and found no association with PTH testing rate for each facility. None of the individual facility-level variables of the complexity score were associated with PTH testing across the 130 facilities. In a comparison of facilities in the top quartile versus the bottom quartile of the PTH testing, there was an association between PTH testing and the presence of stone specialty care at each facility. There was no association between PTH testing and the mean number of parathyroidectomies performed at each facility.
Study limitations cited by the authors included the high proportion of male participants, using a single definition of PHPT, and the inability to capture medical care for veterans with kidney stones who received care outside the VHA system.
In conclusion, the researchers said, “In this cohort study, a generally low rate of PTH testing was found in veterans with kidney stones and hypercalcemia, and extensive variation in PTH testing rates was found across VHA facilities in the United States. More awareness of the level or frequency of elevated serum calcium concentration may be associated with higher rates of PTH testing in patients with kidney stones. Improved screening for PHPT could increase the rates of detection and treatment of PHPT and decrease stone recurrence associated with missed or untreated PHPT.”
- Results of a study designed to examine the prevalence of parathyroid hormone (PTH) testing in US veterans with kidney stones and hypercalcemia and to identify the demographic, geographic, and clinical characteristics of those more or less likely to receive testing.
- The proportion of patients with kidney stones and hypercalcemia was 24.8% (1873/7561); testing rates varied widely across the 130 Veterans Health Administration facilities (range, 4% to 57%).
- Of the 717 patients with biochemical evidence of primary hyperparathyroidism, 26.4% (n=189) underwent parathyroidectomy within 2 years of a stone diagnosis.