Reduced Kidney Function and Relative Hypocalciuria—Observational, Cross-Sectional, Population-Based Data

Abstract

This observational, cross-sectional, epidemiological analysis investigated relationships of kidney function to urine calcium and other variables. The analyses targeted two population-based samples of adults (Gubbio study and Moli-sani study: n = 3508 and 955, respectively). Kidney function was assessed as estimated glomerular filtration rate (eGFR). Calcium/creatinine ratio (Ca/Cr) was used as index of urinary calcium in timed overnight urine under fed condition (Gubbio study), morning urine after overnight fast (Gubbio study), and first-void morning urine (Moli-sani study). Moli-sani study included also data for glomerular filtered calcium load, tubular calcium handling, and serum phosphorus, parathyroid hormone, 1,25-dihydroxyvitamin D, calcium, and 25-hydroxyvitamin D. eGFR positively and independently related to Ca/Cr (p < 0.001). In multivariate analyses, eGFR lower by 10 mL/min × 1.73 m2 related to overnight urine Ca/Cr lower by 14.0 mg/g in men and 17.8 mg/g in women, to morning urine Ca/Cr lower by 9.3 mg/g in men and 11.2 mg/g in women, and to first-void urine Ca/Cr lower by 7.7 mg/g in men and 9.6 mg/g in women (p < 0.001). eGFR independently related to glomerular filtered calcium load (p < 0.001) and did not relate to tubular calcium handling (p ≥ 0.35). In reduced eGFR only (<90 mL/min × 1.73 m2), low urine Ca/Cr independently related to low serum 1,25-dihydroxyvitamin D (p = 0.002) and did not relate to hyperphosphatemia, high serum parathyroid hormone, or hypocalcemia (p ≥ 0.14). Population-based data indicated consistent associations of lower kidney function with lower urine calcium due to reduction in glomerular filtered calcium. In reduced kidney function, relative hypocalciuria associated with higher prevalence of low serum 1,25-dihydroxyvitamin D.

Relationship of the Intake of Water and Other Beverages With Renal Endpoints: Cross-Sectional and Longitudinal Data—Observational, Population-Based Study

“…The analyses included data of the baseline examination, after-baseline data on incidence of renal/kidney replacement therapy and mortality, and data of the 2001-2007 examination, from hereon named as follow-up. The baseline examination comprised a timed urine collection under fed condition from the first void after the evening meal to the first void at the morning wake-up included [11][12][13] ; an early morning blood sample collected under fasting conditions after the completion of the overnight urine collection 9,15 ; a morning timed urine sample under fasting conditions collected after blood sampling for assessment of kidney tubule functions 16,17 ; and a medical visit for measurements of anthropometry and blood pressure and for the administration by trained physicians of questionnaires on socioeconomic status, lifestyles, dietary habits, and medical history. 9,15 The follow-up examination comprised the collection of an early morning blood sample under fasting conditions, a medical visit for measurements of anthropometry and blood pressure, and for the administration of questionnaires on lifestyles and medical history.…”

Urinary Potassium and Kidney Function Decline in the Population—Observational Study

“…With regard to collection of biological samples, the exam-1 protocol included a daytime, untimed, spot urine sample and a venous blood sample after a fast of at least two hours [ 21 , 22 ]. The exam-2 protocol included a timed urine collection under fed condition from the first void after the evening meal to the first void at the morning wake-up included [ 22 , 25 , 26 , 27 , 28 , 29 ], an early morning blood sample collected under fasting conditions after the completion of the overnight urine collection [ 22 , 25 , 26 , 27 , 28 , 29 ], and a morning timed urine sample under fasting conditions collected after blood sampling [ 32 , 33 ]. The exam-3 protocol included the collection of an early morning blood sample under fasting conditions only [ 22 ].…”

The case for a ketogenic diet in the management of kidney disease

“… 104 105 Moreover, studies of kidney stones have largely precluded patients with CKD where their urine parameters change alongside diminishing kidney function. A retrospective study of 811 patients with kidney stones noted that advancing kidney disease afforded reduced calcium stone formation, presumably due to reduced calciuria 106 and increased uric acid stone formation. 107 Metabolic acidosis resulting in acidic urine pH is common among individuals with CKD.…”