The goal of this clinical trial is to evaluate the accuracy and feasibility of transdermal glomerular filtration rate (tGFR) assessment using relmapirazin (Lumitrace) and the MediBeacon tGFR system compared to plasma clearance measurement of GFR in adults with heart failure.

The main question it aims to answer is the comparison of the transdermal-derived GFR for each participant using the MediBeacon tGFR to their nGFRBSA measurement.

Participants will participate in a Screening visit that will take place within 15 days of the scheduled administration of Lumitrace and iohexol. On dosing day, participants will have the tGFR reusable sensor with disposable adhesive ring placed on their chest, and the MediBeacon Transdermal GFR System initiated to collect background fluorescence. Following an injection of Lumitrace and iohexol and the initiation of GFR assessments, participants will be followed at the study center for 10-24 hours. All participants will participate in a follow-up phone call approximately 7 days after the last exposure to Lumitrace and iohexol. Researchers will analyze the results to compare the tGFR values to the nGFRBSA measurements for each participant.

Inclusion Criteria:

1. Age ≥18 years;

   1. Eligible female non-pregnant participants who are either not of child-bearing potential or willing to use adequate contraception during the trial
   2. Males must be willing to practice abstinence or utilize adequate contraception from dosing day to at least 7 days post-dose
   3. For women of child-bearing potential, the participant should have a negative serum pregnancy test at screening, and agrees to one of the following acceptable contraceptive methods used consistently and correctly i.e. abstinence, oral contraceptive either combined or progesterone alone; injectable progesterone, implants of levonorgestrel, estrogenic vaginal ring, percutaneous contraceptive patches, IUD device or system or male partner sterilization
   4. Men will not donate sperm during the study and for 1 month following the last dose of study drug.

2. Diagnosis of symptomatic heart failure: Subject has symptomatic heart failure, ACC/AHA Stage C or D, ambulatory or hospitalized for heart failure, adjudicated by a principal investigator, and meeting both of the following:

   1. Clinical syndrome: Symptoms and/or signs consistent with heart failure (e.g., dyspnea, fatigue, edema, rales, elevated JVP), and

   2. Objective evidence of heart failure (≥1 of):

      • Left ventricular systolic dysfunction or other structural abnormalities (left atrial enlargement, left ventricular hypertrophy, diastolic dysfunction on echocardiography) or
      • Hemodynamic evidence of elevated filling pressures by invasive or noninvasive assessment, or
      • Elevated natriuretic peptides obtained within 90 days from enrollment: NT-proBNP ≥300 pg/mL (BNP ≥100 pg/mL) in sinus rhythm or NT-proBNP ≥900 pg/mL (BNP ≥300 pg/mL) in atrial fibrillation

3. Participants who are capable of directly providing informed consent and who can comply with the requirements and restrictions required by the protocol

4. Adequate venous access sufficient to allow blood sampling per protocol requirements

Exclusion Criteria:

To be eligible for the study, participants must not meet any of the criteria noted below:

1. Intolerance to iohexol or iodine allergy
2. Known allergy to relmapirazin or severe hypersensitivity reactions to adhesives or related products
3. Administration of iohexol for cross-sectional imaging within a week from the dosing visit
4. Limb amputation
5. Primary kidney disease (e.g., glomerulonephritis or polycystic kidney disease)
6. Acute kidney injury (AKI) or unstable kidney function at the time of dosing visit
7. Clinical signs of excessive volume overload (edema grade 3-4 or ascites)
8. Significant scarring, tattoos, or alterations in pigmentation on the sternum or other sensor location areas that would alter sensor readings
9. Use of tanning sprays, tanning products, etc. on the upper chest within 2 weeks of dosing day
10. Use of make-up, lotions, Vaseline or other products on the area of the upper chest on the day prior to or the day of dosing
11. Participants who have received nephrotoxic agent or signs or symptoms suggestive of a condition that may result in acute kidney injury within two weeks of study entry.