Phosphate Assessment in Chronic Kidney Disease Patients Study (PACK)

A Pilot Feeding Study to Assess Phosphate Overload in Patients With Chronic Kidney Disease

The proposed pilot feeding study aims to explore novel pathways in phosphate metabolism and identify new biomarkers, as well as to develop a compound index for assessing phosphate overload with high validity and reliability.

Investigators will address the following specific aims: 1). To explore novel pathways of phosphate metabolism and assess the influence of CKD status on these metabolic pathways. 2). To identify novel biomarkers for phosphate overload that reflect changes in dietary phosphorus intake. 3). To develop a compound phosphate overload index that measures dietary phosphorus intake with high validity and reliability.

This study will provide novel insights into phosphate metabolism and the assessment of phosphate overload in CKD patients. This investigation aims to provide preliminary data to further studies for the development of reliable biomarkers in CKD patients, which could contribute significantly to early interventions and improve health outcomes.

Study Overview

• Status: Recruiting
• Conditions: Chronic Kidney Disease Mineral and Bone Disorder; Chronic Kidney Disease (Stage 3-4)
• Intervention / Treatment: Dietary supplement: Dietary Phosphorus Intake

Detailed Description

Specifically, study team propose recruiting 30 participants with CKD and 30 without CKD to investigate the responses of blood metabolites and known biomarkers to a 21-day diet intervention. The intervention will consist of a dietary phosphorus intake of about 777 mg/day for 7 days, followed by an increase to about 1,277mg/day for another 7 days, and a further increase to about 1,777 mg/day for the subsequent 7 days. 1200 mg/day and 1700 mg/day phosphorus diets will be achieved by providing participants with sodium phosphate capsules and 777 mg/day meals. The meal plan will maintain consistent intake of calories, sodium, potassium, and calcium throughout the 21-day intervention. Sodium, calcium, and potassium content will not change significantly throughout the intervention. The overnight fasting blood and 24-hour and random urine samples will be collected at the baseline and end of each phase.

• Study Type: Interventional
• Enrollment (Estimated): 60
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Alexandra Hartman; Phone Number: 214-645-8294; Email: pack.utsw@utsouthwestern.edu
• Study Contact Backup: Name: Paola Lanza, MD; Phone Number: 469-852-9550; Email: paola.lanza@utsouthwestern.edu

Study Locations

• United States
  • Texas
    • Dallas, Texas, United States, 75390
      • Recruiting
      • University of Texas Southwestern Medical Center
      • Contact: Paola Lanza, MD; Phone Number: 469-852-9550; Email: paola.lanza@utsouthwestern.edu
      • Contact: Alexandra Hartman; Phone Number: 2146458294; Email: pack.utsw@utsouthwestern.edu
      • Principal Investigator: Jing Chen, MD, PhD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Men or women aged 18 years or older, of any race/ethnicity
• Women must either be post-menopausal or have no monthly menstrual cycle
• Estimated total daily energy expenditure (TDEE) of 1700 - 2700 calories
• eGFR >15 ml/min/1.73m2 - < 60 ml/min/1.73m2 for the CKD group (CKD Stage 3 or Stage 4)
• eGFR ≥ 60 ml/min/1.73m2 and negative urine protein on dipstick test for the non-CKD group
• English speaking

Exclusion Criteria:

• Pregnant, currently breastfeeding, or <3 months postpartum
• Current dialysis or kidney transplant patient
• Current use of insulin or chemotherapy drugs
• Smokes cigarettes or uses e-cigarettes (vapes)
• Uses nicotine products or other recreational drugs
• Medical history of stroke or myocardial infarction (MI)
• Medical history of conditions that can affect phosphate metabolism (i.e., uncontrolled thyroid disorder, parathyroid disorder, or gastrointestinal malabsorption disorders [Crohn's, ulcerative colitis, and celiac disease], cirrhosis)
• Current use of certain medications that directly alter phosphate levels (i.e., phosphate binders; phosphate supplements, irregular use of iron)
• Regular use of laxatives
• Hypo- or hyperphosphatemia (serum phosphate < 2.5 or > 4.6 mg/dl)
• Hypo- or hypercalcemia (serum calcium < 8.4 or > 10.7 mg/dl)
• Severe anemia (hemoglobin < 8 g/dl for women and < 9 g/dl for men)
• Severe hyperglycemia (serum blood glucose > 300 mg/dl)
• Body weight less than <110 lbs (due to risk for phlebotomy-induced anemia)
• Received a blood transfusion in the last four months
• Extreme hypertension as demonstrated by a blood pressure > 180/120 as the average of 3 blood pressures taken during the screening/baseline, or extremely low blood pressure < 80/50
• Unwilling or unable to eat study meals
• Lack of access to a functional refrigerator or freezer
• Lack of access to a microwave or conventional oven
• On low potassium diet
• On low phosphate diet
• Specific dietary restrictions (i.e. vegetarian, vegan, ketogenic, etc.)
• Food allergies including but not limited to milk, egg, soy, nuts, shellfish, and wheat or gluten
• Allergic to sodium phosphate
• Unable or unwilling to complete urinary sample collection or food diaries
• Unable or unwilling to provide informed consent
• Unable to read or speak English
• Participant in other conflict clinical trial
• Unable to complete the study measurements
• Unsafe to participate in this study per investigator's judgement

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Diagnostic
• Allocation: Non-Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Chronic Kidney Disease Patients; Participants with eGFR >15 ml/min/1.73m2 - < 60 ml/min/1.73m2 for the CKD group	Dietary supplement: Dietary Phosphorus Intake; Dietary phosphorus intake of about 777 mg/day for 7 days, followed by an increase to about 1,277mg/day for another 7 days, and a further increase to about 1,777 mg/day for the subsequent 7 days. The meal plan will maintain consistent intake of calories, sodium, potassium, and calcium throughout the 21-day intervention. 1200 mg/day and 1700 mg/day phosphorus diets will be achieved by providing participants with sodium phosphate capsules and 777 mg/day meals.
Active Comparator: Control Group; Healthy participants without CKD eGFR ≥ 60 ml/min/1.73m2	Dietary supplement: Dietary Phosphorus Intake; Dietary phosphorus intake of about 777 mg/day for 7 days, followed by an increase to about 1,277mg/day for another 7 days, and a further increase to about 1,777 mg/day for the subsequent 7 days. The meal plan will maintain consistent intake of calories, sodium, potassium, and calcium throughout the 21-day intervention. 1200 mg/day and 1700 mg/day phosphorus diets will be achieved by providing participants with sodium phosphate capsules and 777 mg/day meals.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in serum phosphate levels	Circulating serum phosphate levels (mg/dL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in parathyroid hormone (PTH) levels	Circulating PTH levels (pg/mL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in C-terminal Fibroblast Growth Factor 23 (FGF23) levels	Circulating C-terminal FGF23 levels (RU/mL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in Fibroblast Growth Factor 23 (FGF23) levels	Circulating FGF23 levels (pg/mL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Phosphate burden indices	Phosphate burden indices, developed using machine learning methods to systematically incorporate both known biomarkers and novel biomarkers. No units have been identified, we anticipate creating a score.	Baseline, week 1, week 2, week 3

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in serum calcium levels	Circulating serum calcium levels (mg/dL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in Alkaline Phosphatase (ALP) levels	Circulating serum ALP levels (U/L) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in 1,25-dihydroxyvitamin D levels	Circulating serum 1,25-dihydroxyvitamin D levels (pg/mL) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in Bone-Specific Alkaline Phosphatase (BALP) levels	Circulating serum BALP levels (U/L) will be measured using standard clinical laboratory assays	Baseline, week 1, week 2, and week 3
Change in urinary calcium levels	Circulating urinary calcium excretion levels (mg/day) will be measured using standardized laboratory urine assays	Baseline, week 1, week 2, and week 3
Change in urinary phosphorus levels	Circulating urinary phosphorus excretion levels (mg/day) will be measured using standardized laboratory urine assays	Baseline, week 1, week 2, and week 3

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Exploratory: Phosphate-related biomarkers identified using proteomics platforms	For the proteomics analysis, only novel biomarkers associated with the phosphate diet will be reported, and their quantitative values are expressed as relative fluorescence units (RFU).	Baseline, week 1, week 2, week 3
Exploratory: Phosphate-related biomarkers identified using metabolomics platforms	For the metabolomic analysis, only novel biomarkers associated with the phosphate diet will be reported. These features are not yet chemically identified, quantitative results are expressed as relative abundances.	Baseline, week 1, week 2, week 3

Collaborators and Investigators

• Sponsor: University of Texas Southwestern Medical Center
• Investigators: Principal Investigator: Jing Chen, MD, University of Texas Southwestern Medical Center

Study record dates

Study Major Dates

• Study Start (Actual): May 9, 2025
• Primary Completion (Estimated): December 31, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: November 17, 2025
• First Submitted That Met QC Criteria: January 16, 2026
• First Posted (Actual): January 27, 2026

Study Record Updates

• Last Update Posted (Actual): January 28, 2026
• Last Update Submitted That Met QC Criteria: January 26, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: chronic kidney disease; feeding study; pilot; study diet; oral phosphate feeding
• Additional Relevant MeSH Terms: Urogenital Diseases; Endocrine System Diseases; Bone Diseases; Musculoskeletal Diseases; Pathologic Processes; Nutrition Disorders; Male Urogenital Diseases; Kidney Diseases; Urologic Diseases; Female Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Chronic Disease; Disease Attributes; Metabolic Diseases; Renal Insufficiency; Bone Diseases, Metabolic; Parathyroid Diseases; Avitaminosis; Deficiency Diseases; Malnutrition; Rickets; Calcium Metabolism Disorders; Vitamin D Deficiency; Hyperparathyroidism, Secondary; Hyperparathyroidism; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Renal Insufficiency, Chronic; Chronic Kidney Disease-Mineral and Bone Disorder
• Other Study ID Numbers: STU-2024-1240; 68418 (Other Identifier: UT Southwestern Medical Center)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: IRB approval is required before sharing IPD.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No