Assessing Arterial Flow via Pulse Oximeter Plethysmographic Waveforms

Introduction

Pulse oximetry measures blood oxygen saturation non-invasively using photoplethysmography (PPG), which produces a plethysmographic waveform (pleth wave) reflecting pulsatile blood flow in the microvasculature. Clinicians have explored using the shape and amplitude of this waveform at distal sites (toes or fingers) to assess peripheral arterial blood flow. In patients with risk factors for vasculopathy – such as diabetes mellitus or peripheral arterial disease (PAD) – the pleth waveform might serve as a quick indicator of arterial sufficiency in outpatient settings. A robust, pulsatile pleth wave on a toe suggests adequate perfusion, whereas a dampened or absent waveform may indicate impaired macro- or microcirculation in the limb ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). This section reviews clinical studies and guidelines on the accuracy and utility of pulse oximeter pleth waves for evaluating peripheral circulation, especially in at-risk patients, and how this method compares to standard vascular tests like the ankle-brachial index (ABI) and Doppler ultrasound.

Diagnostic Accuracy of Plethysmographic Waveforms

Several studies have evaluated the sensitivity and specificity of pulse oximetry waveform analysis for detecting peripheral arterial disease or inadequate limb perfusion. In general, these studies place a pulse oximeter on the patient’s toe and consider the test abnormal if the toe’s oxygen saturation is significantly lower than a finger’s or if the waveform flattens upon limb elevation. The results have varied:

• Asymptomatic Diabetics (Parameswaran et al., 2005): In a landmark study of 57 diabetes patients without claudication, toe pulse oximetry (defined as ≥2% drop in toe SpO₂ vs finger or with 12-inch foot elevation) detected PAD with 77% sensitivity and 97% specificity (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). This was comparable to the ABI (63% sensitivity, 97% specificity in the same cohort) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). The reference standard was Doppler waveform analysis of leg arteries (PAD defined by monophasic Doppler waveforms). Notably, combining pulse ox and ABI raised sensitivity to 86% (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). The authors concluded that toe pulse oximetry was as accurate as ABI for LEAD screening in diabetic patients and could serve as a useful additional tool (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...).

• Diabetic Foot Clinic Patients (Deiparine et al., 2018): A study in type 2 diabetics ≥50 years old found pulse ox screening had 76.7% sensitivity and 85.3% specificity for hemodynamically significant PAD (≥50% stenosis on duplex ultrasound) ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). In contrast, the ABI in this population had only 40.7% sensitivity (with 88.2% specificity) ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). Pulse oximetry here involved checking for an SpO₂ gradient >2% between the toe and finger. These results suggest pulse ox was far more sensitive than ABI in this diabetic cohort, likely because arterial calcification in diabetes can falsely elevate ABI readings (making ABI less reliable) ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). The authors reported a positive predictive value ~77% and negative predictive value ~85% for the pulse ox test in detecting duplex-confirmed PAD ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ).

• Diabetes Outpatients (Ena et al., 2013): In a larger diabetes clinic sample (223 patients), a finger-to-toe SpO₂ difference >2% (with foot at 0° and 30° elevation) had lower sensitivity (42.6%) for PAD, with 79.1% specificity ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ). PAD was defined by ABI < 0.9 in that study. The lower sensitivity here contrasts with the above studies – possibly because ABI was used as the gold standard (which can miss disease in diabetics with incompressible vessels). Indeed, the authors noted that 11% of patients had no readable toe oximetry signal and were excluded ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ). They concluded that while easy to perform, “pocket” pulse oximeters alone were insufficiently sensitive for PAD screening in diabetes ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ).

To summarize these findings, toe plethysmography tends to have high specificity (~85–97%) for significant PAD – meaning a normal waveform/saturation is usually reassuring (few false negatives) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ). Sensitivity estimates, however, range more widely (around Forty to 77% in studies) ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...), influenced by methodology and patient factors. Sensitivity appears higher when an independent imaging standard is used ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ) or when combining plethysmography with provocative maneuvers (like limb elevation) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). Table 1 compares the diagnostic accuracy of pulse oximetry versus ABI from two representative studies:

Study (Population)	Reference Standard	Pulse Ox Sensitivity	Pulse Ox Specificity	ABI Sensitivity	ABI Specificity
Parameswaran et al. 2005   medscape.com  (Asymptomatic type 2 DM)	Doppler waveform (LEAD = monophasic)	77%	97%	63%	97%
Deiparine et al. 2018   pmc.ncbi.nlm.nih.gov  (Diabetic foot clinic patients)	Duplex ultrasound (≥50% stenosis)	76.7%	85.3%	40.7%	88.2%

 

Table 1: Sensitivity and specificity of toe pulse oximetry plethysmography vs. ABI in detecting lower-extremity arterial disease, from two studies in diabetic populations. Pulse oximetry was considered abnormal if toe oxygen saturation dropped ≥2% (compared to finger or with leg elevation). Both studies demonstrate pulse ox has comparable or higher sensitivity than ABI, with high specificity in diabetics (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ).

Overall, these data indicate that a detectable, normal pleth waveform in the toe strongly suggests adequate arterial inflow, whereas an abnormal reading (significant saturation drop or waveform attenuation) raises suspicion for arterial insufficiency. The variability in sensitivity underscores that the pleth test may not catch every mild case of PAD – so it is most reliable as a rule-out test (good NPV) or as part of a multi-modal assessment, rather than a standalone definitive diagnostic.

Pleth Waveforms as an Initial Screening Tool

Because pulse oximeters are cheap, portable, and already ubiquitous in clinics, using the pleth waveform as a quick screening tool for peripheral circulation is very attractive. The question is whether it can serve as an initial check for arterial sufficiency in at-risk patients (for example, diabetics during routine foot exams, or patients with a history of PAD). The evidence so far suggests:

• High Specificity Helps Confirm Adequate Flow: If a toe exhibits a strong, pulsatile waveform and normal oxygen saturation (within ~2% of a finger reading) at rest, it is likely that significant large-vessel PAD is absent (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). In Parameswaran’s diabetic cohort, for instance, a normal toe pleth test missed only ~23% of true PAD cases (sensitivity ~77%) but correctly reassured 97% of those without disease (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). Thus, a normal pleth waveform could “screen out” patients with no significant arterial disease, obviating more complex tests in those cases ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ).

• Enhanced Detection in Diabetics: Diabetic patients often have falsely normal ABIs due to calcified arteries. In this context, toe plethysmography has shown higher sensitivity than ABI. Deiparine et al. found pulse ox flagged nearly 77% of diabetic legs with arterial stenoses, whereas ABI alone caught only 40% ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). Combining ABI with pulse ox (declaring a screening positive if either test is abnormal) raised detection to ~88% sensitivity ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). These findings support using the pleth waveform alongside ABI as an initial screen in diabetes to improve case-finding (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...).

• Rapid and Non-Invasive: A pulse ox test can be done in minutes during an office visit. Clinicians have devised simple protocols – e.g. measure finger and toe O₂ saturation in supine position and after modest leg elevation – to stress the circulation (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). An abnormal response (toe saturation drop with elevation, or baseline toe saturation >2% below finger) is taken as a positive screen. This “pleth test” adds very little time or cost, making it appealing as a first-line screening, especially in primary care or endocrine clinics where specialized vascular equipment might not be readily available ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ).

• Limitations: As a screening tool, pleth waveforms are not foolproof. A normal waveform does not completely exclude moderate PAD, especially if collaterals maintain toe perfusion. Conversely, false positives can occur (for example, vasospasm or a cold extremity could dampen the waveform). In Ena et al.’s study, many diabetics had unreadable or low-quality signals, leading to indeterminate results ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ). Proper sensor placement (often on the great toe or a toe free of ulceration) and a warm environment are needed for reliable readings. Poor microcirculation (for example, severe small-vessel disease or edema) could theoretically reduce pleth waveform amplitude even if large arteries are open, though in practice the pleth test is more often discussed in relation to large-vessel PAD. Researchers caution that plethysmography should not completely replace ABI or Doppler in patients with high suspicion of PAD – rather, it can be an adjunct or preliminary test (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...).

In summary, plethysmographic assessment can serve as an initial screening step for arterial sufficiency in outpatient settings. A positive (abnormal) finding would prompt confirmatory testing (e.g. ABI measurement, toe-brachial index, or Doppler ultrasound), while a negative (normal) finding provides some reassurance. Clinical studies in diabetics support this approach, with one concluding that “pulse oximetry may be a useful additional tool to screen for LEAD in patients with diabetes” (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). Importantly, clinical context and judgement should guide interpretation – for instance, a diabetic patient with foot ulceration or rest pain merits full vascular workup even if the toe pulse ox waveform appears normal.

Comparison with Other Vascular Assessment Modalities

To put the pleth waveform in context, it’s useful to compare its performance and role to standard vascular assessment tools:

• Ankle-Brachial Index (ABI): ABI is the ratio of ankle systolic pressure to brachial pressure. It is the usual first-line test for PAD. In general populations, ABI < 0.90 has sensitivity ~60–95% and specificity ~95% for angiographic PAD ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). However, in diabetes or chronic kidney disease, ABI can be falsely high (>1.30) due to arterial calcification, reducing its utility (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology) (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). As noted, toe plethysmography often outperforms ABI in these patients ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). For example, in diabetic limbs with calcified arteries, ABI missed a majority of PAD cases that pulse ox detected ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). That said, ABI remains very specific when low – in Parameswaran’s study both ABI and pulse ox had 97% specificity (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). Some guidelines suggest measuring ABI in all at-risk patients and if ABI is >1.40 or normal but suspicion remains, then proceed to toe-based tests (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology).

• Toe-Brachial Index (TBI): The TBI is analogous to ABI but uses toe systolic pressure (measured with a small PPG sensor and toe cuff) divided by arm pressure. It directly assesses distal perfusion and is less affected by calcification. Meta-analyses show TBI has higher sensitivity (~80–85%) than ABI in diabetic populations, though often at the cost of lower specificity (~66%) (A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes - PubMed) (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). For instance, a systematic review found in diabetics, pooled sensitivity of TBI was 83% vs 63% for ABI (A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes - PubMed). TBI is considered positive if < 0.70 or < 0.60 depending on the cutoff used (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). Many experts consider TBI the preferred test in diabetic patients with suspected PAD and non-compressible ankle arteries. The plethysmographic waveform from a pulse ox is essentially a simplified form of toe PPG, but unlike a formal TBI measurement (which quantifies blood pressure), the pulse ox provides qualitative waveform and saturation data. A normal pleth waveform can roughly correlate with a normal toe pressure, but it does not give an actual pressure index. Thus, while TBI is a more established quantitative measure, a quick pulse ox waveform check is easier and can be done without a cuff. In practice, an abnormal pulse ox screen might lead the clinician to order formal ABI/TBI testing for confirmation.

• Handheld Doppler Ultrasound (Waveform and pulses): Using a Doppler probe to audibly detect arterial pulses and assess waveform quality is a common clinical practice. Triphasic or biphasic Doppler waveforms in pedal arteries indicate decent arterial flow, whereas a monophasic, dampened Doppler signal suggests significant PAD. Doppler waveform analysis was used as the diagnostic standard in some studies (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). A qualitative Doppler exam requires skill but can be done in the clinic. Pleth waveform vs Doppler: Both are assessing pulsatile flow – one via volume/optical changes, the other via blood velocity sounds. Normahani et al. (2021) reviewed studies and reported that simply visualizing the tibial artery waveform (for multi-phasic vs mono-phasic) had a pooled sensitivity of ~83% and specificity ~87% in diabetics (A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes - PubMed). This is comparable to the pulse ox performance in the best-case scenarios. The pleth waveform has the advantage of being easier for non-specialists (just watch the pulse ox waveform on the screen), whereas Doppler provides more direct information about the artery. In practice, these can complement each other: a quick pulse ox waveform check for presence of pulsatile flow, followed by Doppler ABI or waveform exam if needed.

• Oscillometry and Pulse Volume Recording: Some clinics use automated blood pressure cuffs with oscillometric sensors to calculate ABI, or pneumatic cuffs on limbs to record volume pulse waveforms (pulse volume recording, PVR). These modalities also detect attenuation of pulse wave amplitude in PAD. They require specific devices, whereas a pulse oximeter is more readily available. Comparative studies of oscillometric ABI vs pulse ox are limited, but both aim to simplify PAD detection. The pulse volume waveform (measured with cuff plethysmography) can provide a waveform analogous to PPG. Normahani’s review noted one study of pulse volume waveforms and one of “pulse reappearance time” – indicating interest in various waveform-based indices () (). The principle is that all these methods look for dampened peripheral pulses as a sign of arterial insufficiency.

• Transcutaneous Oxygen (TcPO₂): Unlike the above, TcPO₂ assesses microcirculatory oxygen delivery in tissue (often used in wound healing prognosis). It’s not a screening tool for PAD per se, but rather gauges if capillary-level perfusion is sufficient. It involves a heated sensor and is less convenient. Pulse ox pleth wave is not equivalent to TcPO₂, but a normal pleth wave does imply that some oxygenated blood is reaching the area. In cases of very poor microcirculation (e.g. critical limb ischemia), both TcPO₂ and the pleth waveform will be abnormal (TcPO₂ low, and pulse ox perhaps unable to even register a waveform). Guidelines for diabetic foot ulcers often recommend measuring either TBI or TcPO₂ if large-vessel disease is suspected, to ensure adequate perfusion for healing. A present toe pleth waveform can be a quick check that there is at least pulsatile flow, but TcPO₂ provides a quantitative measure of microvascular oxygenation which pulse ox cannot directly give.

In essence, the plethysmographic waveform method occupies a niche between simple pulse palpation and formal vascular testing. It is more objective than palpating a foot pulse, and can reveal subtle flow reductions, but it provides less quantitative detail than ABI/TBI or Doppler. Table 2 (below) synthesizes findings from meta-analyses for various tests in patients with diabetes (where ABI can be problematic):

Test Modality (in diabetics)	Pooled Sensitivity	Pooled Specificity	Source
Ankle-Brachial Index (ABI <0.9)	~60–65%	~87–89%	Normahani 2021); Chuter 2021 meta
Toe-Brachial Index (TBI <0.6)	~83%	~66%	Normahani 2021; CCS Guidelines 2022
Tibial Doppler Waveform (qualitative)	~83%	~87%	Normahani 2021
Pulse Ox Pleth (Toe)	~77% (range 43–77% in studies)	~97% (range 79–97%)	Parameswaran 2005; Ena 2013  Ena 2013

Table 2: Diagnostic performance of PAD tests in diabetes. ABI accuracy drops in diabetics due to vessel calcification (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). Toe-based tests (TBI or pulse ox plethysmography) and waveform analysis can improve sensitivity (A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes - PubMed). (Pooled estimates are from systematic reviews; pulse ox pleth values are illustrative from individual studies as no broad pool available.)

As shown, pulse oximeter waveform analysis has diagnostic accuracy on the order of these other modalities. It is not superior in every aspect, but its ease-of-use makes it an attractive initial test. In practice, a clinician might use a combination: for example, perform ABI and a pulse ox waveform check together – a strategy that has been recommended to maximize sensitivity while retaining specificity (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...).

Guidelines and Expert Recommendations

Major vascular and diabetes guidelines acknowledge the challenges of PAD diagnosis in outpatient settings, especially in diabetics, and they offer some guidance on alternate assessments. However, few formal guidelines explicitly mention pulse oximetry waveforms as a screening tool, since this remains a relatively new or supplementary idea. Below are relevant recommendations and expert opinions:

• Ankle and Toe Indices in Guidelines: The American Heart Association (AHA) and American College of Cardiology (ACC) guidelines on PAD (2016) emphasize ABI as the first-line diagnostic for PAD, and recommend toe-brachial index or Doppler waveform analysis if ABI is >1.40 (incompressible) or normal despite high suspicion (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology) (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). The International Working Group on the Diabetic Foot and other diabetes-related guidelines similarly advise obtaining toe pressures or TcPO₂ in diabetics when ABIs are unreliable, to avoid missing PAD. These guidelines do not specifically say “use a pulse oximeter,” but the principle of assessing toe perfusion is well established. In effect, using a pulse ox pleth waveform is a simplified way to assess toe perfusion before proceeding to these more quantitative tests.

• Use in Outpatient Clinics: Some experts in primary care have championed photoplethysmography for PAD detection. A 2015 review in the British Journal of General Practice noted that “a simpler variant of PPG, pulse oximetry, has already been successfully deployed in general practice” for PAD assessment ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). It advocated for developing PPG devices for routine use in PAD screening, as part of projects like the UK NOTEPAD study ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). The review highlighted that PPG waveforms dampen with PAD (reduced amplitude, delayed upslope) and that a device providing clear interpretation of these waveforms could help GPs stratify patients: reassuring those with no significant PAD and referring those with likely disease ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). This reflects a growing consensus that advanced PPG technology holds promise for primary care PAD screening.

• Consensus Statements: While no formal society guideline (NICE, AHA, etc.) explicitly endorses pulse oximeter pleth waves as a standalone screening, several research groups recommend it as part of a multimodal approach. For example, Parameswaran et al. (2005) suggested adding pulse ox to routine diabetes foot exams to unmask asymptomatic LEAD (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...). Normahani et al. (2021) concluded that pulse oximetry “demonstrated some promise, warranting further investigation” alongside TBI and Doppler waveforms in diabetics (). The Canadian Cardiovascular Society’s 2022 guidelines list pulse oximetry among emerging technologies for PAD diagnosis, though they note data is still limited compared to ABI/TBI (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology). Overall, the expert tone is that pulse ox plethysmography is a useful adjunct – especially in settings without immediate access to Doppler – but it has not yet replaced standard methods in guidelines.

• Outpatient Workflow Recommendations: In practice, some clinicians have integrated the pleth waveform into their PAD screening workflow. A reasonable approach in an outpatient clinic (e.g. diabetes clinic or primary care) is:

  1. Initial screening: Check pedal pulses by palpation and place a pulse oximeter on a toe. Observe the waveform and SpO₂. If the waveform is strong and saturation normal, significant PAD is unlikely (though not impossible). If the waveform is weak/absent or saturation significantly lower than expected, treat it as a positive screen.

  2. Follow-up testing: For patients with abnormal findings or high-risk features, perform an ABI measurement. If ABI is inconclusive (>1.3 or normal but high suspicion remains), proceed to toe pressure (TBI) or refer for a vascular lab assessment (which may do segmental pressures, Doppler waveform analysis, or arterial ultrasound).

  3. Management decisions: Use the results to guide referrals – for example, a patient with an abnormal pleth waveform and ABI <0.9 should be managed as PAD (lifestyle and risk factor modification, and possibly vascular specialist referral). A normal screen in an asymptomatic patient might simply lead to routine risk factor management and periodic re-checks.

This approach aligns with the goals outlined in the BJGP review: to quickly identify those with no significant disease (who can be monitored conservatively) and those with probable disease (who need further evaluation) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ). It’s essentially how one would use any screening test, with the understanding that pulse oximetry is a triage tool, not a definitive test.

In conclusion, pulse oximeter plethysmographic waveforms have shown clinical utility in assessing peripheral circulation in at-risk outpatients. Studies demonstrate that a toe pleth wave analysis can detect hemodynamically significant PAD with moderate-to-high sensitivity and high specificity (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ). It can be especially helpful in diabetic patients where ABI may be misleading. While it is not yet a universally endorsed standalone test, the pleth waveform is increasingly recognized as a convenient screening option. Current best practice would use it in conjunction with traditional modalities – leveraging its speed and ease to improve initial PAD detection, and then confirming diagnoses with ABI, TBI, or Doppler studies as needed (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) (). As technology and primary care experience evolve, we may see broader guideline support for PPG-based assessments of microcirculation in the future, helping to ensure patients with PAD are identified early and accurately in the outpatient setting.

Sources:

• Parameswaran G.I. et al. (2005). Arch Intern Med, 165(4):442-446 – Pulse ox vs ABI in asymptomatic diabetics (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...) (Toe Pulse Oximetry May Help Detect Lower Extremity Arterial Disease in...).

• Deiparine, R. et al. (2018). J ASEAN Fed Endocr Soc, 33(2):160-167 – Pulse ox vs ABI vs duplex in diabetic PAD ( Pulse Oximetry as a Screening Test for Hemodynamically Significant Lower Extremity Peripheral Artery Disease in Adults with Type 2 Diabetes Mellitus - PMC ).

• Ena J. et al. (2013). J Diabetes Mellitus, 3(2):79-85 – Pocket pulse ox in diabetes clinic (low sensitivity) ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ) ( Use of pocket pulse oximeters for detecting peripheral arterial disease in patients with diabetes mellitus ).

• Normahani P. et al. (2021). J Vasc Surg, 73(5):1811-1820 – Systematic review (ABI, TBI, pulse ox in diabetics) (A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes - PubMed) ().

• Canadian Cardiovascular Society PAD Guidelines (2022) – on ABI limitations in diabetes and alternate tests (TBI, waveform) (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology) (Canadian Cardiovascular Society 2022 Guidelines for Peripheral Arterial Disease - Canadian Journal of Cardiology).

• Haining S., Allen J. (2015). Br J Gen Pract, 65(635):e612-e614 – Review of PAD diagnosis challenges and PPG potential ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ) ( Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help - PMC ).