Toe-Brachial Index (TBI) Calculator

The index for a limb whose ankle pressure cannot be trusted: hallux systolic pressure over the higher brachial pressure, with the 0.70 threshold and the absolute toe pressures the published criteria use.

Last updated 8 Oct 2026

Toe-brachial index

Hallux over higher brachial

Hallux systolic pressure (mmHg)The great toe’s systolic pressure, from a digital cuff and a photoplethysmograph rather than a Doppler. Romanos and colleagues describe the technique: a 2.5 by 9 cm cuff on the proximal hallux, the probe on the pulp, 20 minutes lying flat with the room at 20 to 22 degrees C, inflation to a maximum of 200 mmHg, and the systolic pressure read as the waveform returns. A cold foot gives a low toe pressure for reasons that have nothing to do with disease.

Right brachial systolic pressure (mmHg)The denominator is the higher of the two arms, exactly as for the ankle-brachial index, so both arms are measured.

Left brachial systolic pressure (mmHg)Taking the higher arm gives the lower index, which is the conservative direction and the published convention.

0.42Example

Hallux 62 mmHg, right brachial 148 mmHg, left brachial 140 mmHg

Formula

TBI = hallux systolic pressure / higher brachial systolic pressure

hallux systolic pressure: the great toe’s systolic pressure, from a digital cuff with a photoplethysmograph. Romanos and colleagues define the index as “toe systolic pressure divided by brachial systolic pressure”
higher brachial systolic pressure: the higher of the two arms, the same denominator the ankle-brachial index uses. The ACC/AHA guideline calls the toe-brachial index “the ratio of the first toe pressure divided by the highest brachial artery pressure”
0.70: the diagnostic threshold, stated differently by the two guidelines: ACC/AHA says 0.70 or less is diagnostic, ESVS 2024 says below 0.7 is abnormal. Exactly 0.70 therefore falls either side depending on which you read
why the toe rather than the ankle: the digital arteries are much less affected by medial calcification than the crural arteries. Romanos and colleagues note that toe measures “are reported to be less affected by medial calcification” and that Monckeberg’s sclerosis is “highly prevalent in autonomic neuropathy and chronic renal insufficiency”. That is the clinical case for this index: it is what you reach for when the ABPI is above 1.40 or implausibly normal
absolute toe pressure, in mmHg: a separate published criterion and not a ratio. Below 30 mmHg defines critical ischaemia in the Second European Consensus Document and TASC; Rutherford’s standard uses below 30 mmHg for category 4 and below 40 mmHg for categories 5 and 6
what it cannot do: diagnose chronic limb-threatening ischaemia. The ACC/AHA guideline says so explicitly of both indices, with at least a quarter of those patients having borderline or normal values

Worked example

Hallux 62 mmHg, right brachial 148 mmHg, left brachial 140 mmHg
Brachial pressure, higher arm: max(148, 140) = 148 mmHg. 62 / 148 = 0.42, at or below the published diagnostic threshold
The absolute toe pressure of 62 mmHg is above both published absolute criteria (30 mmHg for critical ischaemia, 40 mmHg for Rutherford category 5), so the ratio and the absolute pressure are saying different things — which is why both are reported
Three points on the same formula. With the same arms, a toe pressure of 100 mmHg gives 0.68; 120 mmHg gives 0.81; and 28 mmHg gives 0.19, with an absolute pressure below the 30 mmHg critical-ischaemia criterion as well
Both sides of the boundary. 103 / 148 = 0.70 and falls in the 0.70-or-less band; 105 / 148 = 0.71 and does not. An index of exactly 0.70 — a toe pressure of 98 mmHg against a brachial pressure of 140, say — also falls in the lower band, because the ACC/AHA wording is inclusive. The ESVS 2024 wording is not, and would put the same limb the other side
The denominator still matters. Dividing the same 62 mmHg by the left arm's 140 instead of the higher 148 gives 0.44. Small here, but the same mistake on a borderline limb moves it across 0.70

The two published thresholds, and what each source says

The difference is one value wide and it is real: a limb at exactly 0.70 is diagnostic under the first and not under the second. The calculator uses the inclusive form and says so rather than hiding the choice.
Source	Threshold	Wording
ACC/AHA lower extremity PAD guideline (AFP summary)	0.70 or less	“A toe-brachial index of 0.70 or less is diagnostic for PAD”
ESVS 2024, asymptomatic PAD and intermittent claudication	Below 0.7	“A TBI lower than 0.7 is considered abnormal”

Absolute toe pressures the published criteria use

These are pressures, not ratios, and that is deliberate: the ratio moves when the arm moves. A toe at 45 mmHg is the same toe whether the brachial pressure is 110 or 180, but the index is 0.41 or 0.25. Where a published criterion is in mmHg, use the mmHg.
Toe pressure	Criterion	Source
Below 30 mmHg	Defines critical ischaemia	Second European Consensus Document and TASC, quoted by Romanos 2010
Below 30 mmHg	Rutherford category 4, ischaemic rest pain	Rutherford 1997 reporting standard
Below 40 mmHg	Rutherford categories 5 and 6, tissue loss	Rutherford 1997 reporting standard
40 to 90 mmHg	The range observed in a diabetic cohort	Romanos 2010, descriptive rather than a normal range

The index you reach for when the ankle lies

The toe-brachial index exists because of a specific failure of the ankle-brachial index. Medial arterial calcification stiffens the crural arteries so that a cuff cannot occlude them at the true intraluminal pressure; the measured ankle pressure then reads high, and the index comes out normal or above 1.40 in a limb that may be severely ischaemic. The digital arteries are much less affected. Romanos and colleagues record that toe measures “are reported to be less affected by medial calcification” and that Monckeberg’s sclerosis, the lesion responsible, is “highly prevalent in autonomic neuropathy and chronic renal insufficiency” — which is the population in whom the ankle index is least trustworthy and this one most useful.

The arithmetic is the same shape as the ankle index: a distal systolic pressure over the higher of the two brachial pressures. The measurement is not. A toe pressure needs a digital cuff and a photoplethysmograph rather than a Doppler, and it is temperature-sensitive in a way an ankle pressure is not. The protocol Romanos and colleagues describe — cuff on the proximal hallux, probe on the pulp, twenty minutes lying flat, the room at 20 to 22 degrees C, inflation to a maximum of 200 mmHg — is not fussiness. A cold foot gives a low toe pressure for reasons that have nothing to do with arteries.

Two numbers come out of the test and they are not substitutes for each other. The index is a ratio, and it falls when the arm pressure rises even though nothing has changed in the foot. The absolute toe pressure is a pressure, and it is what the published critical-ischaemia criteria are written in: below 30 mmHg in the Second European Consensus Document and TASC, below 30 mmHg for Rutherford category 4 and below 40 mmHg for categories 5 and 6. Where a criterion is stated in millimetres of mercury, read the millimetres of mercury. What this index cannot do is close a case: the ACC/AHA guideline states that neither index “are not useful for the diagnosis of chronic limb-threatening ischemia”, and that at least a quarter of those patients have borderline or normal values.

This category owns the limb and the named vessel. Risk estimation in somebody with no vascular diagnosis belongs to the pooled cohort equations, the cost of an operation to the Revised Cardiac Risk Index and the AUB-HAS2 index, and central circulatory arithmetic to systemic vascular resistance and mean arterial pressure.

Frequently asked questions

What is a normal toe-brachial index?

Above the diagnostic threshold, which the two guidelines read for this page state slightly differently: the ACC/AHA guideline says 0.70 or less is diagnostic of peripheral arterial disease, and the ESVS 2024 guideline says below 0.7 is abnormal. A result of exactly 0.70 is therefore abnormal under one and not the other.

When should a toe-brachial index be measured instead of an ABPI?

When the ankle index cannot be trusted. The ACC/AHA guideline says that “For noncompressible arteries (ABI of more than 1.40), the toe-brachial index should be measured”, and ESVS 2024 recommends it on suspicion of a falsely elevated ankle index. In practice that means long-standing diabetes, chronic kidney disease, and any limb whose ankle pressure looks better than the foot does.

Why does the absolute toe pressure matter as well as the ratio?

Because the published critical-ischaemia criteria are written in millimetres of mercury and a ratio can be moved by the arm. A toe at 45 mmHg gives an index of 0.41 against a brachial pressure of 110 and 0.25 against 180, with no change in the foot. Below 30 mmHg defines critical ischaemia in the Second European Consensus Document and TASC; Rutherford uses below 30 mmHg for category 4 and below 40 mmHg for categories 5 and 6.

Can a toe-brachial index rule out limb-threatening ischaemia?

No. The ACC/AHA guideline states that neither this index nor the ankle-brachial index is useful for diagnosing chronic limb-threatening ischaemia, and that at least 25 per cent of those patients have borderline or normal values. A foot with tissue loss needs more than a ratio.

Does the toe pressure have to be measured with the patient lying flat?

The published protocol says so, and also specifies the temperature. Romanos and colleagues had participants lie supine with the legs at heart level for twenty minutes with the room at 20 to 22 degrees C. StatPearls records that sitting rather than lying raises the ankle index by approximately 0.3 — a measurement artefact larger than most of the thresholds on this page.

Related calculators

References

American Academy of Family Physicians. Management of Lower Extremity Peripheral Artery Disease: Guidelines From the ACC/AHA. Am Fam Physician. 2025;112(5).
Romanos MT, Raspovic A, Perrin BM. The reliability of toe systolic pressure and the toe brachial index in patients with diabetes. J Foot Ankle Res. 2010;3:31.
American Academy of Family Physicians. AHA Releases Recommendations on Ankle-Brachial Index Measurement and Interpretation. Am Fam Physician. 2013;88(12):866 — summarising Aboyans V, Criqui MH, Abraham P, et al., Circulation. 2012;126(24):2890–909.
StatPearls. Ankle-Brachial Index. Treasure Island, FL: StatPearls Publishing, 2025.
Articl. Rutherford Classification of Chronic Limb Ischemia, reproducing Rutherford RB, Baker JD, Ernst C, et al., J Vasc Surg. 1997;26(3):517–38.

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/