Work Instruction (WI) is a controlled document that describes, step by step, how a single task is performed at the point of use. In medical device manufacturing, a work instruction sits below a standard operating procedure, converts specifications into repeatable operator actions, and supplies the objective evidence auditors expect under ISO 13485:2016.
What is a Work Instruction (WI)?
A work instruction is the most granular layer of a quality management system’s document hierarchy. Above it sit the quality manual, quality policy, and standard operating procedures (SOPs). An SOP says what a process does and who owns it. A WI says how one person, at one station, completes one task: torque a housing screw, load a reflow profile, reconcile a label reel before release.
Because a WI is written for the person doing the work, it is specific rather than general. It names the fixture, the setting, the acceptance criterion, and the record to be completed. Work instructions typically live inside or alongside the Medical Device File (ISO 13485:2016 clause 4.2.3), which the FDA now recognizes in place of the Device Master Record.
Why Work Instruction (WI) matters in medical device development
Manufacturing variation is a patient safety problem before it is a yield problem. A cleaning step run at the wrong dwell time can leave residue on an implant. A miswired harness can drop a monitor’s alarm. Work instructions are how validated process parameters reach the people building the device.
They also carry regulatory weight. ISO 13485:2016 clause 7.5.1 requires production under controlled conditions, with documented procedures, work instructions, and reference materials available where the work happens. Clause 4.2.4 requires those documents to be reviewed, approved, versioned, and kept legible at the point of use. Since February 2, 2026, the FDA’s Quality Management System Regulation (QMSR) has replaced the Quality System Regulation in 21 CFR Part 820 and incorporates ISO 13485:2016 by reference, so those clause obligations now sit inside US federal requirements.
Auditors know this. Outdated instructions at a workstation, an uncontrolled printout taped to a bench, or a procedure no operator can follow as written are easy findings. Each raises a fair question: Is the process that made the device the process that was validated?
Key components of a Work Instruction (WI)
Format varies by company and task. Content should not. A usable device-industry WI carries:
- Control data. Document number, revision, effective date, approver, and the SOP it supports.
- Scope. Which product, line, or station does the instruction govern?
- Prerequisites. Operator qualification, tooling and fixture IDs, calibration status, and gowning or ESD requirements.
- Sequential steps. Numbered actions in order, one per step, written in the imperative.
- Acceptance criteria. Torque values with tolerances, temperatures, dwell times, and visual standards. No step should make an operator guess a number.
- Visual aids. Annotated photographs or drawings for orientation-sensitive assembly.
- Records generated. The traveler, batch record, or Device History Record entry the step feeds.
- Nonconformance handling. What to do when the step fails, and where escalation goes.
Good instructions are written against the validated process, not against habit. When IQ/OQ/PQ establishes a proven acceptable range, the WI carries that operating window. When an ISO 14971 risk control depends on a manufacturing step, the WI is where it becomes real.
Common challenges and best practices
The most common failure is drift. A process changes on the floor, the change never reaches document control, and the WI stops describing reality. Change control is the fix, but only if it is fast enough that people use it rather than route around it.
The second failure is writing for the auditor instead of the operator. Instructions padded with regulatory language and paragraph prose get skimmed. Short imperative steps, one action each, with the needed number on the same line, are followed.
Other patterns worth watching:
- Translation quality. If the line and the document owner speak different languages, translate and verify. A mistranslated tolerance is a defect waiting to happen.
- Training linkage. ISO 13485:2016 clause 6.2 ties competence to the tasks people perform. A revised WI usually implies retraining, and the record should show it.
- Point-of-use control. Electronic display through an MES removes stale printouts and timestamps who read which revision.
- Cluttered visuals. Photograph the actual fixture, not a prototype. One clear image beats four decorative ones.
Write the first draft with an operator next to you. Then have someone who has never done the task follow it. Whatever they ask about is what the document is missing.
How SJML helps with Work Instruction (WI)
Syrma Johari MedTech is an end-to-end medical device CDMO operating under ISO 13485 across multiple manufacturing sites, with ISO Class 7 and 8 cleanrooms and ESD-controlled environments. SJML manufacturing teams build and maintain the process documentation behind PCBA, molding, precision metal, box build, and packaging operations, tied to process validation (IQ/OQ/PQ), PFMEA, and SAP-integrated MES traceability. Structured change governance keeps instructions current while limiting revalidation burden, and design transfer carries validated parameters from engineering into shop-floor instructions.
Talk to SJML’s manufacturing team →
Frequently asked questions
An SOP describes a process at the level of scope, roles, inputs, and outputs. It answers what happens and who is accountable. A work instruction describes one task inside that process: individual physical actions, settings, and acceptance criteria. One SOP for solder assembly may point to a dozen work instructions, one per station or product variant.
ISO 13485:2016 does not mandate a work instruction for every task. Clause 7.5.1 requires production under controlled conditions with documented procedures, work instructions, and reference materials available as needed. The organization decides, on a risk basis, which tasks need instructions and how detailed they must be. That decision should be defensible during an audit.
The QMSR became effective on February 2, 2026, and incorporates ISO 13485:2016 by reference into 21 CFR Part 820. Practical expectations for controlled, current, point-of-use manufacturing documentation did not change in substance. What changed is the citation: manufacturers now map their document hierarchy to ISO clauses rather than to legacy Part 820 subparts.
The person who knows the task and the person who owns the process, together. Process engineering usually drafts, an experienced operator reviews for realism, and quality approves for control. Approval routing and revision history must follow the document control procedure required by ISO 13485:2016 clause 4.2.4.
Related terms
- Standard Operating Procedure (SOP)
- Device History Record (DHR)
- Process Validation
- Change Control
- Batch Record
