Systemic Inflammation Response Index (SIRI) Calculator
Systemic Inflammation Response Index (SIRI) Calculator
Calculate SIRI — the neutrophil-lymphocyte ratio with the monocyte brought in. Seven studies of the same cancer put the cut-off anywhere between 0.69 and 2.35, which tells you what a cut-off is worth here.
Systemic Inflammation Response Index (SIRI)
N × M ÷ LNeutrophils 4.8, monocytes 0.55, lymphocytes 1.6 (all ×10⁹/L)
The formula, and the convention its cut-offs assume
counts in ×10⁹/L (= ×10³/µL)
SIRI in cells/µL = SIRI in ×10⁹/L × 1,000
- N × M / L
- the formula is stated identically in every source consulted — a cervical cancer study, a metastatic pancreatic cancer study, a neurosurgical series and an ANCA-vasculitis cohort all give neutrophil count times monocyte count over lymphocyte count
- what it adds to NLR
- the monocyte. NLR is neutrophils over lymphocytes; SIRI multiplies that by the monocyte count. Monocytes are the precursors of tumour-associated macrophages and of the myeloid-derived suppressor cell compartment, so the claim is that they carry signal the two-cell ratio misses
- the factor of 1,000
- two counts in the numerator and one in the denominator, so going to cells/µL multiplies SIRI by 1000² ÷ 1000 = 1,000. This is visible in the literature: pancreatic cut-offs cluster around 1 to 2, while an ANCA-associated vasculitis study reports its cut-off as 2847.9 mm⁻³. Same index, different convention
- no reference interval
- as with every index in this family, none has been established in a healthy population. The bands here describe the published literature
Worked example
Neutrophils 4.8, monocytes 0.55, lymphocytes 1.6 (all ×10⁹/L)
4.8 × 0.55 = 2.64
2.64 ÷ 1.6 = 1.65
Below 1.8, the median cut-off across seven pancreatic cancer studies and the figure attributed to the original Qi paper
The NLR for the same patient is 4.8 ÷ 1.6 = 3.0 — already above the conventional NLR cut-off. Multiplying by a monocyte count of 0.55 pulls the index down, because a monocyte count below 1.0 makes SIRI smaller than NLR
That is worth understanding: SIRI is NLR scaled by the monocyte count, so it only exceeds NLR when monocytes are above 1.0 ×10⁹/L
In cells/µL the same patient scores 4,800 × 550 ÷ 1,600 = 1,650 — a thousand times larger, and the reason a published cut-off of 2847.9 and one of 2.35 can both be real
Seven studies, one cancer, seven cut-offs
| Study | Year | Cut-off |
|---|---|---|
| Qi et al. — the original SIRI paper | 2016 | 1.8 |
| Li et al. | 2019 | 0.69 |
| Topkan et al. | 2021 | 1.8 |
| Dâmaso et al. | 2022 | 1.34 |
| Kamposioras et al. | 2022 | 2.35 |
| Kim et al. | 2022 | 0.95 |
| Pacheco-Barcia et al. | 2024 | 2.3 |
Two more cut-offs, read directly, in other diseases
| Setting | Cut-off | How derived |
|---|---|---|
| Metastatic pancreatic cancer, 2025 single-centre cohort | 1.86 | ROC analysis on the study’s own data |
| Cervical cancer | 1.25 | Youden index on the study’s own data |
| ANCA-associated vasculitis | 2847.9 mm⁻³ | ROC analysis — and note the units: this is the cells/µL convention, equivalent to about 2.85 in ×10⁹/L |
The family, and why they agree with each other
| Index | Formula | What it adds |
|---|---|---|
| NLR | N ÷ L | The baseline: neutrophilia with lymphopenia |
| PLR | P ÷ L | The platelet arm instead of the neutrophil arm |
| LMR | L ÷ M | Inverted — a high value is the favourable direction |
| SII | P × N ÷ L | Platelets on top of NLR |
| SIRI | N × M ÷ L | Monocytes on top of NLR |
| PIV | N × P × M ÷ L | Both |
What the monocyte adds, and why seven cut-offs is none
The systemic inflammation response index is the neutrophil count multiplied by the monocyte count and divided by the lymphocyte count. Arithmetically it is the neutrophil-lymphocyte ratio scaled by the monocyte count, which has a consequence worth noticing at the outset: because a normal adult monocyte count is well below one, SIRI is usually a smaller number than the NLR for the same patient, and it only exceeds it when monocytes rise above 1.0 ×10⁹/L.
The monocyte is the whole argument for the index. Circulating monocytes are the precursors of tumour-associated macrophages and overlap with the monocytic myeloid-derived suppressor cell compartment, both of which are immunosuppressive within a tumour; a marker built only on neutrophils and lymphocytes cannot see them. Qi and colleagues introduced SIRI in 2016 in pancreatic cancer after chemotherapy, and the pancreatic literature has stayed its centre of gravity ever since — which makes it, unusually for this family of markers, an index with a coherent single-disease evidence base rather than a scattering of one-off cohorts.
That evidence base is also what makes the cut-off problem impossible to argue away. A 2024 meta-analysis pooled seven pancreatic cancer studies and found their thresholds for ‘high SIRI’ were 0.69, 0.95, 1.34, 1.8, 1.8, 2.3 and 2.35 — a three-and-a-half-fold range, in one tumour type, with a pooled overall survival hazard ratio of 2.40. Each threshold was derived by ROC analysis or a Youden index on the study’s own outcome data, which is a procedure that will always produce a number and will produce a different number every time. The pooled hazard ratio says that SIRI carries prognostic information; it does not say that any particular value of SIRI means anything about a particular patient.
Units compound this. Two of the three counts sit in the numerator, so switching from ×10⁹/L to cells per microlitre multiplies the index by a thousand. The pancreatic literature works in ×10⁹/L and reports cut-offs between 0.69 and 2.35; a study of ANCA-associated vasculitis, using the same formula, reports its cut-off as 2847.9 mm⁻³. Read without its unit that looks like a different marker. Read with it, it is 2.85, and it sits just above everyone else’s range. Any SIRI quoted without its convention is not a number.
Which leaves the honest summary. SIRI, NLR, PLR, LMR, SII and PIV are a correlated family — five share a lymphocyte denominator, four share a neutrophil numerator — all of them driven by the same underlying physiology of neutrophilia with lymphopenia under stress. They are prognostic, in cohorts, retrospectively. They are not diagnostic, none is in any major guideline, and no cut-off among them has been prospectively validated as a decision rule. Used as one variable among many in a prognostic model, they are reasonable. Used as a number to act on for one person in front of you, none of them has earned it.
Frequently asked questions
What is the SIRI formula?
Neutrophil count multiplied by monocyte count, divided by lymphocyte count, all as absolute counts. The pancreatic cancer literature in which the index was developed works in ×10⁹/L, which is the same as ×10³/µL.
What does SIRI add over the neutrophil-lymphocyte ratio?
The monocyte count. Monocytes are precursors of tumour-associated macrophages and of monocytic myeloid-derived suppressor cells, both immunosuppressive in tumours, and a two-cell ratio cannot capture them. Arithmetically SIRI is NLR scaled by the monocyte count, so it is smaller than NLR whenever monocytes are below 1.0 ×10⁹/L.
What is a high SIRI?
There is no agreed threshold. Seven pancreatic cancer studies pooled in a 2024 meta-analysis used cut-offs of 0.69, 0.95, 1.34, 1.8, 1.8, 2.3 and 2.35, with a median of 1.8. Each was optimised on its own cohort’s outcome data.
Why does one paper report a SIRI cut-off of 2847.9?
Because it is working in cells per microlitre. Two of the three counts are in the numerator, so that convention gives a value a thousand times larger. 2847.9 in that convention is 2.85 in ×10⁹/L, which sits just above the range used in the pancreatic literature.
How is SIRI different from PIV?
PIV adds the platelet count to the numerator, so it uses all four cell lines where SIRI uses three. That also makes PIV’s unit discrepancy a factor of a million rather than a thousand, and its published cut-offs span the hundreds rather than single figures.
Should a raised SIRI change management?
Not on its own. It is a prognostic marker derived from retrospective cohorts, correlated with every other index built from the same counts, absent from every major guideline, and never validated as a decision rule for an individual patient.
Related calculators
References
- Qi Q, Zhuang L, Shen Y, et al. A novel systemic inflammation response index (SIRI) for predicting the survival of patients with pancreatic cancer after chemotherapy. Cancer. 2016;122(14):2158–2167.
- Prognostic role of systemic inflammation response index (SIRI) in patients with pancreatic cancer: a meta-analysis. Front Oncol. 2024;14:1465279.
- SIRI as a prognostic marker in metastatic pancreatic cancer. Medicina (Kaunas). 2025;61(11):2020.
- Systemic inflammation response index predicts all-cause mortality in patients with antineutrophil cytoplasmic antibody-associated vasculitis. Int Urol Nephrol. 2021;53(7):1477–1484.
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.