Donor Chimerism Percentage Calculator
Donor Chimerism Percentage Calculator
Percentage donor from the peak areas of one informative STR marker after transplantation — and why the direction of travel across serial samples carries more information than any single figure.
Donor Chimerism Percentage
Donor, recipient peak → % donorA donor-specific peak area of 3,860 and a recipient-specific peak area of 640 at one informative marker
Formula
% recipient = 100 − % donor
report the mean across all informative markers, not one marker alone
- informative marker
- one at which donor and recipient alleles are fully distinguishable, so each peak belongs unambiguously to one of them. A marker where they share an allele cannot be used, because the shared peak carries contributions from both. Twelve or more markers are enough to distinguish any donor–recipient pair
- peak area
- measured the same way in both channels, from the same electropherogram. Area and height both work provided one of them is used consistently; mixing them, or comparing a value derived one way with a historical value derived the other, introduces a difference that looks like a change in chimerism
- averaging
- a multiplex assay computes a mean percentage across the informative markers rather than reporting one. Markers amplify with different efficiencies and differ in stutter, so a single locus is noisier than the panel, and a locus that disagrees markedly with the others is a signal to look at the trace rather than a result
- the sensitivity limit
- STR-PCR resolves a minor population down to about 1 to 5% with 1 ng or more of input DNA. Quantitative PCR reaches around 0.1%, digital PCR 0.05 to 0.1% and sequencing-based methods 0.1 to 0.5%. Complete donor chimerism by STR means complete to somewhere between 1 and 5%, and that qualification belongs on the report
- why the trend beats the value
- THE POINT OF THE PAGE: there is no universal threshold at which anything happens. Guidance is explicit that intervention — changing immunosuppression, donor lymphocyte infusion, a second transplant — should be guided by chimerism in the context of the disease and its residual burden. What a single figure cannot show, and a series can, is the direction of travel
Worked example
A donor-specific peak area of 3,860 and a recipient-specific peak area of 640 at one informative marker
Total informative signal = 3,860 + 640 = 4,500
% donor = 3,860 ÷ 4,500 × 100 = 85.8%, so the recipient fraction is 14.2%
That is mixed chimerism, and on its own it means very little. The same 85.8% after a fall from 97% two weeks earlier is an urgent result; after a rise from 60% over three months in a reduced-intensity transplant it is an expected one
Repeat the calculation at every informative marker and report the mean. A single locus carries the stutter and amplification quirks of that locus; the panel average does not
Note the method's floor. STR-PCR resolves a minor population down to about 1 to 5%, so this assay cannot tell 0.5% recipient from 0% — quantitative PCR, digital PCR and sequencing-based assays reach an order of magnitude lower
And note the compartment. A whole-blood figure of 85.8% is a weighted average over every lineage in the sample; the CD34-positive and CD33-positive fractions can be falling while whole blood looks stable, which is where relapse shows itself first
How far down each method can see
| Method | Sensitivity for a minor population | What it is used for |
|---|---|---|
| STR-PCR with capillary electrophoresis | 1–5% (with 1 ng or more of input DNA) | The routine workhorse: informative for any donor–recipient pair with 12 or more markers, quantitative across the whole range, and cheap enough for frequent serial sampling |
| Quantitative PCR of insertion/deletion polymorphisms | About 0.1% | Following a small recipient population below what STR can resolve, and samples with little DNA |
| Digital PCR | 0.05–0.1% | Absolute quantification of a very small minor population without a standard curve |
| Next-generation sequencing | 0.1–0.5% | Sensitivity approaching quantitative PCR with far more informative markers, and no need to pre-select them |
Complete, mixed and declining
| State | What it means | The caveat |
|---|---|---|
| Complete donor chimerism | No recipient-derived cells detected. The ASTCT guideline uses 5% recipient as the detection limit for this definition in lymphoid and myeloid lineages | Detected by what? At STR sensitivity, complete means under about 1 to 5% |
| Mixed chimerism | Donor and recipient haematopoietic cells both present | There is no agreed cut-off: published definitions of mixed chimerism use thresholds anywhere from under 1% to 20% recipient |
| Stable mixed chimerism | A recipient population that persists without growing across serial samples | Expected after reduced-intensity conditioning, and the intended outcome in some non-malignant indications |
| Declining donor chimerism | A donor fraction falling across serial samples | The pattern that matters. It precedes relapse and graft loss, and it is only visible if the sampling interval is short enough to see it |
| Lineage-specific chimerism | The same calculation on a sorted fraction — CD3, CD33, CD34 | More sensitive than whole blood. Decreasing CD34-positive chimerism is an independent risk factor for relapse in acute myeloid leukaemia and myelodysplastic syndrome, and is detectable even in patients whose blood and marrow chimerism look stable |
Why lineage matters: early complete donor chimerism in the myeloid compartment
| Measure | Figure |
|---|---|
| Definition used | Recipient DNA under 0.2% in CD33-positive cells in any blood or marrow sample within 60 days of transplantation |
| Cohort | 154 transplants for acute myeloid leukaemia, 37 relapses (24%) |
| Two-year relapse-free probability with early complete chimerism | 0.76 (95% CI 0.65–0.90) |
| Two-year relapse-free probability without it | 0.42 (95% CI 0.25–0.70) |
| Significance | P = 0.033 |
One number, and the series it belongs to
After an allogeneic haematopoietic transplant, the marrow contains cells from two people, and short tandem repeat genotyping is how their proportions are measured. The principle is genetic identity testing put to a quantitative use: at a marker where donor and recipient carry different alleles, each electrophoretic peak belongs unambiguously to one of them, and the donor’s share of the total informative signal is the donor’s share of the cells. Donor peak divided by donor plus recipient peak, times a hundred. A marker is only usable if the two genotypes are fully distinguishable there, which is why a panel is run rather than a single locus, and why twelve or more markers is enough to separate any donor–recipient pair. The reported figure is the mean across the informative markers, because loci differ in amplification efficiency and in stutter, and a locus that disagrees sharply with the rest is a prompt to look at the trace rather than a result in its own right.
The number needs two qualifications before it can be read, and both are commonly left off. The first is the method’s floor. STR-PCR resolves a minority population down to somewhere between 1 and 5%, with at least a nanogram of input DNA; below that a recipient population is simply not seen. Quantitative PCR of insertion–deletion polymorphisms reaches about 0.1%, digital PCR 0.05 to 0.1%, and sequencing-based assays 0.1 to 0.5%. So a report of complete donor chimerism by STR means complete to within a few per cent — which is entirely adequate for confirming engraftment and entirely inadequate for detecting a returning clone early. The second qualification is the compartment. A whole-blood figure is a weighted average across every lineage in the sample, dominated by whichever is most abundant, and it can stay reassuring while a specific lineage moves. Sorted fractions — CD3 for T cells, CD33 for myeloid cells, CD34 for progenitors — are more informative, and decreasing CD34-positive chimerism is an independent risk factor for relapse in acute myeloid leukaemia and myelodysplastic syndrome that is detectable even in patients whose blood and marrow chimerism appear stable.
The vocabulary around the result is less settled than it sounds. Complete donor chimerism means no recipient cells detected, and the one definition with a body’s name attached uses 5% recipient as the detection limit in lymphoid and myeloid lineages. Mixed chimerism means both populations are present, and there the definitions diverge badly: published thresholds for what counts as mixed range from under 1% to 20% recipient, an order of magnitude of disagreement hiding inside a single phrase. When a result moves between centres, the method and the definition have to travel with the number, or two perfectly correct reports will appear to contradict each other.
Which brings us to the thing the calculator cannot do. There is no threshold at which something happens. Guidance is explicit that the need for and the type of intervention — adjusting immunosuppression, a donor lymphocyte infusion, a second transplant — should be guided by chimerism in the context of the disease being treated and any residual malignant cells, rather than by a figure. Mixed chimerism after reduced-intensity conditioning is expected; in some non-malignant indications a stable mixed state is the goal rather than a shortfall. What distinguishes a tolerable mixed chimerism from a dangerous one is not its value but its direction: 86% donor reached by rising from 60% over three months and 86% reached by falling from 97% in a fortnight are the same number describing opposite situations. Serial sampling at an interval short enough to see the slope is what makes chimerism monitoring worth doing, and a single percentage reported without its predecessors has thrown away most of its information. The same logic applies to the sensitivity choice: a trend measured at 1 to 5% resolution shows a large change late, and a trend measured at 0.1% shows a small change early.
Frequently asked questions
How is donor chimerism calculated from STR peaks?
Divide the donor-specific peak area by the sum of the donor and recipient peak areas at an informative marker and multiply by 100. A donor peak of 3,860 against a recipient peak of 640 gives 85.8% donor. Repeat at every informative marker and report the mean, since loci differ in amplification efficiency and stutter.
What counts as an informative marker?
One where the donor and recipient genotypes are fully distinguishable, so each peak belongs to only one of them. A marker where they share an allele cannot be used quantitatively. Twelve or more STR markers are enough to distinguish any donor–recipient pair, and the informative ones are established from pre-transplant donor and recipient samples.
How sensitive is STR-PCR chimerism testing?
It resolves a minor population down to about 1 to 5%, with 1 ng or more of input DNA. Quantitative PCR of insertion–deletion polymorphisms reaches about 0.1%, digital PCR 0.05 to 0.1% and next-generation sequencing 0.1 to 0.5%. Complete donor chimerism by STR therefore means complete to within a few per cent, not absolutely.
What is the difference between complete and mixed chimerism?
Complete means no recipient-derived cells are detected — the ASTCT guideline uses 5% recipient as the detection limit for this in lymphoid and myeloid lineages. Mixed means both populations are present, but published definitions of mixed chimerism use thresholds anywhere from under 1% to 20% recipient, so the term needs its threshold stated.
Why is lineage-specific chimerism more useful than whole blood?
Because a whole-blood result is an average dominated by the most abundant cell type and can look stable while one lineage changes. Decreasing CD34-positive chimerism is an independent risk factor for relapse in acute myeloid leukaemia and myelodysplastic syndrome and is detectable even when blood and marrow chimerism appear stable.
At what chimerism level should treatment change?
There is no universal threshold, and none should be quoted as if there were. Guidance states that the need for and type of intervention — immunosuppression changes, donor lymphocyte infusion, a second transplant — should be guided by chimerism in the context of the disease and its residual burden. The trend across serial samples carries far more information than any single value.
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References
- Picard C, Frassati C, Cherouat N, et al. New methods for the quantification of mixed chimerism in transplantation. Front Immunol. 2023;14:1023116.
- Miura S, Ueda K, Minakawa K, Nollet KE, Ikeda K. Prospects and potential for chimerism analysis after allogeneic hematopoietic stem cell transplantation. Cells. 2024;13(11):993.
- Lindahl H, Vonlanthen S, Valentini D, et al. Lineage-specific early complete donor chimerism and risk of relapse after allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia. Bone Marrow Transplant. 2022;57(5):753–759.
- Kristt D, Stein J, Yaniv I, Klein T. Assessing quantitative chimerism longitudinally: technical considerations, clinical applications and routine feasibility. Bone Marrow Transplant. 2007;39(5):255–268 — and Kristt D et al, Leukemia. 2005;19(6):1169–1172, on computing a mean percentage across multiplexed markers.
- Scharf SJ, Smith AG, Hansen JA, McFarland C, Erlich HA. Quantitative determination of bone marrow transplant engraftment using fluorescent polymerase chain reaction primers for human identity markers. Blood. 1995;85(7):1954–1963.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.