The proposed study is a prospective, observational, investigator and patient blinded study comparing the results of blood volume measurement using the FDA-cleared Daxor BVA-100 device to the Daxor BVA-200 device. Data from this study may be pooled with data from studies with similar design conducted at other sites, for the purposes of an FDA medical device submission.

Measurements of human blood volume will be made via the indicator dilution method, using gamma counter readings of the concentration of I-131 in a subject's blood sample taken after radio-iodinated Human Serum Albumin (HSA) has been injected into the bloodstream via venous access. Each subject receiving an injection will have five separate blood samples taken, which will be analyzed separately. Each of the five measurements will be conducted in duplicate with the BVA-100 instrument and the BVA-200 instrument. Sufficient blood will be withdrawn at each phlebotomy to permit such duplicate measurement.

Subjects will be enrolled who have been prescribed a blood volume procedure using the BVA-100, as a result either of their ordinary diagnostic care or of their participation in another study that uses blood volume measurement. Subjects will be adults under treatment for conditions normally associated with the need for volume assessment, such as Heart Failure, or scheduled to receive BVA-100 measurement as part of another study. An effort will be made to ensure a range of ages and a balance of the sexes.

Subjects will be enrolled and consented sequentially. The University of Tennessee Medical Center site will document any patient who is not enrolled in the study sequentially and the reason why or who declines enrollment. Demographics of patients not enrolled will be collected to permit identification of any trends in non-enrollment. We do not anticipate any sequential patient not being offered the opportunity to participate in order to assure that there is no bias in selection of patients ("all-comers").

Inclusion Criteria:

1. Age: Over18 years;
2. Able and willing to provide informed written consent.
3. Subjects will be enrolled who have been prescribed a blood volume procedure using the BVA-100, as a result either of their ordinary diagnostic care or of their participation in another study that uses blood volume measurement. Subjects will be adults under treatment for conditions normally associated with the need for volume assessment, such as Heart Failure, or scheduled to receive BVA-100 measurement as part of another study.

Exclusion Criteria:

1. Pregnant women or nursing mothers.
2. Women of childbearing potential not using adequate birth control methods.
3. Known hypersensitivity to iodine or eggs.
4. Other clinical basis for precluding the use of radioactive materials.
5. Has previously been enrolled in, and completed, the study.

The proposed study will be open to any volunteer meeting the inclusion/exclusion criteria listed below. We intend to highlight differential analysis of clinical patients from exemplary disease states (such as congestive heart failure and chronic kidney disease), as well as other population characteristics such as age, sex, race, etc.

IPD will not be made available to other researchers.