Bolton NHS — Lean Diagnostic Redesign Eliminates the Scan Bottleneck
Bolton NHS Foundation Trust found that patients were blocking beds not because of social care delays or discharge process failures but because they were waiting for scans and test results. They applied Lean Six Sigma to map the diagnostic pathway, identify waste, and redesign the scheduling system. Scan-to-result time fell from weeks to days. The diagnostic bottleneck dissolved. Bolton used formal SPC tracking throughout — making this the most methodologically rigorous of the five corridor care Bright Spots, and the closest to Bootstrap CUSUM standard.
- Understand how Bolton identified diagnostics (not discharge) as the binding constraint — and why that changes the intervention entirely.
- See how Lean Six Sigma and value stream mapping made the diagnostic bottleneck visible.
- Assess why radiographer skill expansion is a high-sustainability intervention — a capability change that doesn’t reverse when an improvement team leaves.
- Understand why Bolton’s SPC tracking is strong evidence — and what the remaining gap is.
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The constraint Bolton found
Most corridor care improvement programmes start from the assumption that the binding constraint is discharge — patients waiting for social care, waiting for transport, waiting for administrative sign-off. Bolton started from data rather than assumption.
Value stream mapping of patient journeys revealed that a significant proportion of bed-blocking patients were not delayed by discharge processes at all. They were waiting for diagnostic results: scans, biopsies, specialist test results. Until the result arrived, the clinical team could not make a discharge decision. The diagnostic wait was creating an invisible queue of patients who were occupying beds not because they were medically unfit to leave but because a piece of information was missing.
This is the constraint identification insight in practice: the pile of work (corridor patients) was downstream of the constraint (diagnostic backlog), not at it. Adding discharge coordinators or social care capacity would have addressed a non-constraint and produced no change in corridor care.
The Lean Six Sigma approach
Bolton used formal Lean Six Sigma methodology — Define, Measure, Analyse, Improve, Control (DMAIC) — with value stream mapping and SPC throughout. This is methodologically distinctive: most NHS improvement uses PDSA with run charts; Bolton used a more structured approach that produced more precise identification of waste and a more rigorous measurement of the improvement.
The value stream mapping exercise revealed three sources of waste in the diagnostic pathway:
- Rigid booked slots — diagnostics scheduled in advance regardless of patient need, creating queues of inpatients waiting for the next available slot while outpatient bookings occupied earlier slots
- Duplicated imaging — patients moving between wards were sometimes re-imaged because previous imaging was not accessible to the receiving team
- Skill boundaries — certain procedures required radiologists who were backlogged; radiographers with the capability to perform the same procedures were not authorised to do so
The interventions — Joiner level analysis
| Intervention | Joiner level | What changed | Sustainability |
|---|---|---|---|
| Demand-driven diagnostic scheduling — rigid booked slots replaced by flexible queues that prioritise inpatients by clinical urgency | Level 2–3 | Changed the scheduling system so that inpatient need drives slot allocation rather than the booking calendar. Made the constraint (inpatient diagnostic wait) visible in the scheduling system. | High once embedded in radiology scheduling systems. Requires ongoing clinical governance to maintain prioritisation criteria. |
| Radiographer skill expansion — radiographers trained and authorised to perform procedures previously reserved for radiologists | Level 3 | Changed the accountability and capability structure of the diagnostic workforce. Challenged the assumption that only radiologists can perform certain procedures — an Evaporating Cloud injection. Increased diagnostic throughput without adding radiologist capacity. | Very high. Capability change — trained radiographers retain their skills. The most durable intervention in this series. Does not require external support to maintain once the training is embedded. |
| Imaging accessibility — previous imaging made accessible to all clinical teams regardless of ward | Level 2 | Eliminated duplicated imaging by making existing information visible across the system. A direct visibility intervention — the image already existed; the problem was it couldn’t be seen by the team that needed it. | High once embedded in electronic records systems. |
The assumption challenged
The radiographer skill expansion is the most important intervention in Bolton’s programme — not because it had the largest immediate impact, but because it challenged an assumption that had never been examined: that certain diagnostic procedures can only be performed by radiologists.
This assumption was not clinically required. It was a historical professional boundary that had been maintained as a natural law rather than a policy choice. The Evaporating Cloud makes it explicit:
A — Objective: Diagnose inpatients quickly and safely
B — Requirement 1: Diagnostics need to be clinically safe and accurate
C — Requirement 2: Diagnostics need to be available within the clinical timeframe
D: Use radiologists for all procedures
D′: Meet inpatient demand with available radiologist capacity
Conflict: Radiologist capacity is insufficient for the demand; inpatients wait
The assumption: Only radiologists can perform these procedures safely
The injection: Train radiographers to perform the procedures to the same clinical standard. The assumption was a professional boundary, not a clinical requirement. Once challenged and tested, the conflict dissolved.
Sustainability assessment
Bolton is the most likely of the five Bright Spots to be structurally sustained, for the same reason as Criteria-Led Discharge at Ipswich: the radiographer capability change does not reverse when an improvement team leaves. The knowledge is in the workforce.
| Factor | Assessment |
|---|---|
| Radiographer skill retention | Very high. Trained radiographers retain skills through use. As long as the procedures are performed regularly, capability is maintained. |
| Scheduling system design | High once embedded. The demand-driven scheduling system can drift back to rigid booking under administrative pressure, but the system design makes reversion visible. |
| Professional boundary reassertion | Medium risk. Professional boundaries in healthcare are enforced through Royal College guidance, job planning, and consultant contracts. A change in radiological professional guidance or a new consultant preference could re-narrow the radiographer scope. |
| SPC monitoring continuity | Medium. Bolton’s SPC tracking was part of the Lean Six Sigma Control phase. Whether that monitoring has continued beyond the formal project phase is not publicly confirmed. |
Bootstrap CUSUM — the honest position
Bolton is the closest of the five Bright Spots to Bootstrap CUSUM standard evidence. Lean Six Sigma includes formal SPC tracking in its Control phase — Bolton measured diagnostic flow times before and after the intervention and demonstrated sustained special cause variation (improvement) in the post-intervention period. This is stronger than a run chart and consistent with what Bootstrap CUSUM would show.
The remaining gap:
- Pre-committed prediction — DMAIC methodology includes a Measure phase with baseline data, but the formal pre-committed prediction (direction + timeframe + metric + confidence threshold) made publicly before the improvement phase began has not been published
- Corridor care as the outcome — Bolton’s SPC tracking focused on diagnostic flow times; whether corridor care rates were the primary outcome measure or a downstream consequence is not confirmed in public sources
- Balancing measures — diagnostic accuracy rates (did faster diagnosis compromise quality?), radiographer workload and staff experience, and outpatient waiting times (did inpatient prioritisation extend outpatient waits?) should be monitored simultaneously
The honest summary: Bolton has the most rigorous methodology and the strongest internal measurement evidence of the five Bright Spots. The evidence is consistent with genuine structural change in the diagnostic pathway. A full pre-committed Bootstrap CUSUM evaluation with balancing measures would confirm whether corridor care rates changed structurally — and whether the improvement has been sustained beyond the formal project period.