Plasma Dilution
Plasma dilution (neutral blood exchange with saline and albumin)
Written by Aaron CuhaReviewed Sep 2026
Also known as: Neutral blood exchange, NBE, Saline-albumin exchange, Dilution hypothesis
The mouse experiment that asked whether young blood is necessary at all. Replacing half the plasma with saline plus albumin, adding nothing young, matched the effects attributed to young blood.
Overview
Everything in the young-blood field assumes that something in young plasma is doing the work. Plasma dilution is the control experiment for that assumption. In a 2020 paper in Aging, researchers replaced half the plasma volume in mice with saline containing 5 percent albumin, calling this a neutral age blood exchange because nothing young was added and the albumin merely replenished what saline alone would have removed.
A single exchange met or exceeded the effects of heterochronic blood sharing on all the key outcomes: muscle repair, liver adiposity and fibrosis, and hippocampal neurogenesis in old mice. The authors also ran comparative proteomics on serum from the mouse procedure and from the human clinical procedure it resembles, therapeutic plasma exchange, and reported a molecular resetting of systemic signalling in both, with some proteins rising rather than falling. A single human plasma exchange abolished the usual inhibition of progenitor cell proliferation by old serum in their assay. Their proposed model is that diluting autoregulatory proteins that feed back into multiple signalling pathways produces long-lasting changes in gene expression.
No human has received neutral blood exchange as an ageing intervention, and no trial of it is registered. The human analogue is therapeutic plasma exchange, which this site covers separately and which has actual randomised trials, two of which reported opposite results in 2025.
Mechanism of action
Established in mice only. The proposal is that plasma contains autoregulatory proteins whose concentrations feed back on their own production and on multiple signalling pathways, so that diluting them resets those pathways and produces durable transcriptional changes rather than a transient concentration drop. Albumin was added to the exchange fluid to replace what saline alone would have diluted, and the authors state that ectopically added albumin does not appear to be the sole determinant of the effect, noting that albumin levels do not fall with age and do not rise after exchange. The mechanism has not been demonstrated in a person.
Human evidence
No human has received neutral blood exchange as described in the mouse work, and no trial of it is registered under that name. The human evidence that bears on the dilution hypothesis comes from therapeutic plasma exchange trials, which are covered on their own page and which currently disagree with each other.
- The 2020 mouse paper does report one human observation: a single therapeutic plasma exchange in a person abolished the usual inhibition of progenitor cell proliferation by old serum in the authors' in vitro assay. That is a laboratory assay on human serum, not a clinical outcome.
- Aging Cell 2025, 42 healthy adults over 50: plasma exchange with albumin replacement, and in one arm added immunoglobulin, produced rejuvenation across 15 epigenetic clocks versus placebo.
- Scientific Reports 2025, randomised crossover in healthy blood donors: plasmapheresis with no replacement fluid produced no rejuvenation and three clocks moved in the ageing direction. This is the protocol closest to pure dilution and it did not reproduce the mouse result.
What this does not tell you: The strongest human test of dilution without any replacement fluid is the 2025 Scientific Reports crossover trial, and it did not find rejuvenation. That is one small trial with a specific protocol, so it is not decisive, but it is the only direct human check of this hypothesis and it points the other way. Nothing in the human record links any plasma exchange protocol to a health outcome rather than a biomarker.
Reading the research record
This entry exists because it is the field's own control experiment, and it complicates the young-blood story rather than supporting it. If half-volume exchange with saline and albumin reproduces what heterochronic parabiosis does in mice, then the active principle may be removal of old plasma rather than addition of young plasma, and every product sold on the young-blood premise is selling the wrong half of the mechanism. The same authors point at the practical implication: an already-available procedure, therapeutic plasma exchange, would be the route, not a donor plasma product.
The human data now available do not settle it and currently lean against the simplest version. The 2025 trial that came closest to pure dilution, plasmapheresis in healthy blood donors with no albumin or young plasma replacement, found epigenetic clocks moving the wrong way. The 2025 trial that reported rejuvenation replaced the removed volume with albumin and, in its strongest arm, added intravenous immunoglobulin, which is not dilution alone. Both are small. This site publishes both and does not pick a winner.
The evidence, charted
Fig. 1 · evidence composition
2of 4 citations (50%) are in people
Counted from the citation list on this page. The Human count is the same number shown in the badge at the top. Both understate any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 3 distinct years, 2011 to 2025, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Approved
AU
Approved
CA
Not approved
Approved in 2 of 4, prescription route in 0, not approved in 2. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 4 · dose response
No human dose response curve exists
We draw this figure where the data supports it. For this compound in humans it does not, so the panel stays empty rather than borrowing an animal curve and implying it transfers.
Key studies & citations
- Animal2020
Rejuvenation of three germ layers tissues by exchanging old blood plasma with saline-albumin
Mouse. A single exchange of half the plasma volume for saline with 5 percent albumin, adding nothing from a young animal, met or exceeded the effects of heterochronic blood sharing on muscle repair, liver adiposity and fibrosis, and hippocampal neurogenesis in old mice. Comparative proteomics on mouse and human exchanged serum showed a resetting of systemic signalling, with some proteins elevated rather than reduced. NIH funded with non-US government support.
Aging (Albany NY) - Animal2011
The ageing systemic milieu negatively regulates neurogenesis and cognitive function
Mouse. Heterochronic parabiosis showed that blood-borne factors inhibit or promote adult neurogenesis in an age-dependent way, and that old plasma impairs synaptic plasticity and memory in young mice. This is the result that the dilution experiment reinterprets: if old blood is inhibitory, removing it may matter more than adding young blood.
Nature - Human2025
Multi-Omics Analysis Reveals Biomarkers That Contribute to Biological Age Rejuvenation in Response to Single-Blinded Randomized Placebo-Controlled Therapeutic Plasma Exchange
42 healthy adults over 50 randomised to biweekly plasma exchange with or without intravenous immunoglobulin, monthly exchange, or placebo. Fifteen epigenetic clocks showed rejuvenation versus placebo at false discovery rate below 0.05, strongest in the biweekly plus immunoglobulin arm. This is the nearest human test of the dilution idea, and it replaced the removed plasma with albumin.
Aging Cell - Human2025
Human clinical trial of plasmapheresis effects on biomarkers of aging (efficacy and safety trial)
Randomised crossover in healthy blood donors, 8 versus 4 plasmaphereses over 18 weeks with no young plasma and no albumin replacement. No epigenetic rejuvenation was found. DNAmGrimAge, the Hannum clock and the Dunedin Pace of Aging all increased. This is the closest human test of dilution without replacement, and its result runs against the dilution hypothesis.
Scientific Reports
Frequently asked questions
Does removing old blood work as well as adding young blood?
In mice, in one 2020 paper, yes: a single exchange of half the plasma volume for saline plus albumin met or exceeded the effects of young blood on muscle repair, liver fat and fibrosis, and hippocampal neurogenesis. In humans the question is open, and the trial that came closest to testing pure dilution found no benefit.
Has plasma dilution been tested in people?
Not under that name. The closest human tests are therapeutic plasma exchange trials. A 2025 trial with albumin replacement reported rejuvenation across 15 epigenetic clocks against placebo in 42 adults; a 2025 crossover trial with no replacement fluid found no rejuvenation and three clocks moving in the ageing direction.
Why does this matter for young plasma clinics?
Because if dilution is the mechanism, the young donor is not doing the work. That would mean the intervention with evidence behind it is an existing medical procedure rather than a purchased plasma product. The mouse data support that reading; the human data so far do not confirm it.