Phosphorus Absorption in Healthy Adults and in Patients With Moderate Chronic Kidney Disease

Study Overview
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Brief Summary
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Chronic kidney disease (CKD) affects approximately 26 million Americans with many more at risk for disease development. Elevated serum phosphorus (P) and related abnormalities in P homeostasis due to progressive loss of kidney function are primary driving forces behind cardiovascular dysfunction and mortality in CKD patients. Intestinal P absorption is an critical aspect in P homeostasis but has been understudied, particularly in the early stages of CKD progression. This study aims to determine P absorption in patients with moderate CKD compared to healthy adults.

Official Title
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Phosphorus Absorption in Healthy Adults and in Patients With Moderate Chronic Kidney Disease

Conditions
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Chronic Kidney Disease Mineral and Bone Disorder

Intervention / Treatment
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* Other: Phosphorus Absorption Test


Participation Criteria
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Eligibility Criteria
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Inclusion: Men and women ages 30-75 years old, any race Moderate CKD, based on the last set of labs done in the past year, defined as: Glomerular Filtration Rate (GFR) category G3a (eGFR 45-59 mL/min) with A2 or A3 albuminuria or proteinuria by positive dipstick or urine protein/creatinine ratio (UPCR); -or- G3b (eGFR 30-44 mL/min), with or without evidence of albuminuria (any A1-A3) or proteinuria. (Figure 1) -or- Healthy control with no diagnosis or evidence of CKD Female subjects must be post-menopausal, surgically sterile, or confirmed not pregnant by pregnancy test and not breastfeeding. Subjects must be on stable doses of medications (except those noted in exclusion criteria) for at least 6 weeks prior to the study Exclusion: Plans to initiate dialysis within 6 months Labs based on the last set done in the past year: Hypercalcemia defined as serum calcium > 10.5 mg/dL Hyperkalemic > 5.5 mg/dL Prescribed a phosphate binder medication Small bowel resection, bariatric surgery. Medically unstable or poorly controlled hypertension, diabetes, or gastrointestinal disorders in the opinion of the physicians on the study team Calcitriol, ergocalciferol, cholecalciferol, vitamin D analogs, calcimimetics, PTH analogues, calcium supplements, multivitamins/mineral and other medications that may alter phosphorus metabolism - must be off for at least 6 weeks prior to study

Ages Eligible for Study
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Minimum Age: 30 Years
Maximum Age: 75 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Healthy Subjects<br>Healthy subjects, free of CKD | Other: Phosphorus Absorption Test<br>* Subjects will undergo a radiophosphorus (P-33) absorption test over two days, that will include an oral administration of P-33 on the 1st day of the test, and an IV administration of P-33 on the 2nd day of the test. P-33 activity from serial serum and urine collections will be determined by scintillation counting, and fractional phosphorus absorption calculated by kinetic modeling.<br>|
| Moderate CKD Subjects<br>Subjects with moderate-stage CKD | Other: Phosphorus Absorption Test<br>* Subjects will undergo a radiophosphorus (P-33) absorption test over two days, that will include an oral administration of P-33 on the 1st day of the test, and an IV administration of P-33 on the 2nd day of the test. P-33 activity from serial serum and urine collections will be determined by scintillation counting, and fractional phosphorus absorption calculated by kinetic modeling.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Fractional Phosphorus Absorption | Radiophosphorus (P-33) activity determined by liquid scintillation counting in serum and urine after oral and IV administration will be used to determine fractional phosphate absorption. | Measured from serial blood draws over a 4-hour time frame | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Serum FGF23 | serum intact and c-terminal FGF23 | Measured from baseline measures and serial blood draws over a 4-hour time frame | 
| Serum 1,25(OH)2D | serum 1,25-dihydroxyvitamin D | Measured from baseline measures and serial blood draws over a 4-hour time frame | 
| Serum parathyroid hormone (PTH) | serum intact parathyroid hormone | Measured from baseline measures and serial blood draws over a 4-hour time frame | 
| Serum phosphate | serum phosphate | Measured from baseline measures and serial blood draws over a 4-hour time frame | 
| 24h Urine phosphate | 24h urine phosphate | measured from two, 24-hour urine collections | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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chronic kidney disease, CKD, renal failure, phosphorus, phosphate, intestinal absorption