Calibration for Medical Device Manufacturers in Singapore: HSA & ISO 13485 Requirements

The Regulatory Framework for Medical Device Calibration in Singapore

HSA and the Health Products Act

Singapore's Health Products (Medical Devices) Regulations 2010, administered by the Health Sciences Authority (HSA), regulate the manufacture, import, supply, and export of medical devices in Singapore. Medical device manufacturers who hold a Manufacturer's Licence must comply with GMP (Good Manufacturing Practice) requirements, which include documented calibration of measuring and test equipment. HSA conducts GMP inspections of licensed manufacturing facilities, and calibration is a standard element of the inspection checklist.

Inspectors examine the calibration procedure, the list of instruments in scope, calibration certificates, recall systems, and out-of-tolerance investigation records. Deficiencies in the calibration programme can result in observations, major non-conformances, or, in serious cases, suspension of the manufacturing licence.

PIC/S PE 009 for Combination Products

For medical devices that incorporate a medicinal component (combination products), the PIC/S PE 009 GMP Guide for Medicinal Products may apply alongside ISO 13485. PIC/S Chapter 6 (Quality Control) requires that reference standards and measurement instruments be calibrated and traceable to national standards. Manufacturers of combination products must satisfy both ISO 13485 and PIC/S calibration requirements, which are largely aligned but have some differences in documentation format and terminology.

ISO 13485:2016 and its Relationship to ISO 9001

ISO 13485:2016 is the quality management system standard specifically for medical device manufacturers. It is based on ISO 9001 but includes additional requirements that reflect the regulatory environment and risk management obligations of the medical device industry. Critically, ISO 13485 is not merely a "stricter version" of ISO 9001. It imposes specific requirements in several areas (including calibration and OOT investigation) that have no direct equivalent in ISO 9001. ISO 13485 certification is the threshold for FDA-regulated market access via many international distributors and for CE marking under EU MDR.

ISO 13485:2016 Clause 7.6, a Detailed Examination

Clause 7.6, titled "Control of monitoring and measurement equipment," is the calibration clause of ISO 13485. It is worth examining in detail because it is more prescriptive than most quality managers expect.

Scope. What is "Monitoring and Measurement Equipment"?

The scope of Clause 7.6 is broader than most manufacturers initially assume. "Monitoring and measurement equipment" includes:

• Physical measurement instruments: calipers, micrometers, gauges, thermometers, pressure gauges, flow meters, force gauges, torque wrenches, electrical test equipment
• Environmental monitoring instruments: temperature loggers, humidity sensors, particle counters (for controlled manufacturing areas)
• Process monitoring instruments: temperature controllers on ovens and sterilisers, pressure monitors on autoclaves, packaging seal strength testers
• Measurement software: If software is used to perform measurement (e.g. image analysis software used to measure dimensional characteristics), that software must be validated under Clause 7.6. This is frequently overlooked.

The Documented Procedure Requirement

ISO 13485 Clause 7.6 requires a documented procedure for the control of monitoring and measurement equipment. This procedure must define:

• The process for identifying all monitoring and measurement equipment in scope
• How calibration intervals are determined
• How calibration status is identified (labels, records, or database flags)
• The calibration method or reference to the calibration standard used
• The process for handling equipment found out-of-tolerance
• How calibration records are stored and retained

Calibration Status Identification

All instruments within the Clause 7.6 scope must have their calibration status clearly identified. This is most commonly achieved through calibration labels affixed to the instrument showing the calibration date, next due date, calibration reference number, and any limitations on use (e.g. "for use in range 0–50°C only"). Where instruments cannot be labelled (e.g. small probes, wire sensors), a register or database must track their calibration status, and the instruments must be retrievable by identifier to their calibration record.

Protection from Adjustments that Would Invalidate Calibration

Clause 7.6 also requires that instruments be protected from adjustments that would invalidate the calibration setting. For many digital instruments, this means sealing the adjustment access points (e.g. potentiometer holes) with calibration seal stickers that show evidence of tampering if the seal is broken. For instruments with adjustment mechanisms (e.g. zero adjust on a balance), the procedure must specify who is authorised to make adjustments and what re-verification is required after any adjustment.

Out-of-Tolerance (OOT) Investigation in Medical Device Manufacturing

The OOT investigation process is where ISO 13485 diverges most significantly from ISO 9001 in the calibration context. ISO 9001 requires that OOT findings be addressed, but leaves the method largely to the manufacturer. ISO 13485 requires a more formal investigation because the potential consequence (medical devices produced using inaccurate measurement), can have patient safety implications.

The OOT Investigation Process

When an instrument is found out-of-tolerance at calibration (i.e. the as-found measurement is outside the acceptance criteria), the following investigation process is required:

1. Immediate quarantine of the instrument: The instrument must be removed from service pending investigation completion. Calibration records are updated to show the instrument as "out-of-tolerance, under investigation."
2. Determination of the OOT period: Review the instrument's calibration history to determine when the instrument was last found to be in tolerance. The OOT period is the time between the last in-tolerance calibration and the discovery of the OOT condition.
3. Product impact assessment: Identify all products (batches, lots, devices) that were measured or monitored using the OOT instrument during the OOT period. This requires traceability between measurement records and product records. Another reason why instrument identification and record-keeping are critical.
4. Risk assessment: Evaluate whether the out-of-tolerance condition could have affected the product. Consider the magnitude of the OOT error relative to the measurement acceptance criteria used during production. If the OOT error is small relative to the acceptance criteria, the risk to product may be low.
5. Disposition of affected product: Based on the risk assessment, decide whether affected products can be released, require additional testing, or must be quarantined pending further evaluation or disposal.
6. Corrective action: Identify the root cause of the OOT condition (e.g. instrument damage, environmental conditions, calibration interval too long) and implement corrective action to prevent recurrence.

Documentation of OOT Investigations

All steps of the OOT investigation must be documented and retained as part of the calibration record for the instrument. The OOT investigation record must reference the specific product batches assessed, the risk assessment rationale, the disposition decision, and the corrective action. This documentation must be available for HSA GMP inspections and for customer audits.

Records Retention in Medical Device Manufacturing

ISO 13485 Clause 4.2.5 (Records) establishes retention requirements that differ fundamentally from ISO 9001. The standard requires that records be retained for at least the greater of:

• A period defined by applicable regulatory requirements
• The lifetime of the medical device as defined by the organisation
• A minimum of two years from the date of product release

Device Lifetime and Long-Term Retention

For most Singapore medical device manufacturers, the "lifetime of the device" is defined in the device's risk management file (ISO 14971). For short-lifetime devices (single-use consumables, diagnostics), this may be 2–5 years. For implantable devices (orthopaedic implants, cardiovascular devices, cochlear implants), the device lifetime can be 15–30 years or more. This means calibration records for instruments used in the manufacture of implantable devices may need to be retained and accessible for three decades. Digital record management systems with appropriate backup and access controls are essential for managing this long-term retention obligation.

FDA and EU MDR Additional Requirements

Singapore medical device manufacturers who export to the US market must also comply with FDA 21 CFR Part 820 Section 820.72, which requires calibration against equipment with a known valid relationship to nationally or internationally recognised measurement standards. Where no national or international standard exists, the manufacturer must establish and document the basis for calibration. For the EU market, EU MDR (Regulation 2017/745) requires technical documentation to include reference to standards applied, including measurement standards. SAC-SINGLAS accreditation provides the clearest demonstration that calibration has been performed against nationally recognised standards.

IQ/OQ/PQ Calibration Requirements

Process validation in medical device manufacturing follows the IQ/OQ/PQ framework. Each phase requires specific calibration documentation:

Installation Qualification (IQ)

IQ verifies that manufacturing equipment has been installed correctly and that all instruments and utilities are within specification. All measurement instruments used in the IQ phase must have current, valid calibration certificates. The IQ package must list all instruments used, with their calibration certificate numbers, calibration dates, and expiry dates.

Operational Qualification (OQ)

OQ verifies that equipment operates within specified performance limits across its operating range. Measurements taken during OQ (temperatures, pressures, speeds, forces, electrical parameters), must all be made with calibrated instruments. OQ is the most instrument-intensive validation phase; a typical OQ for an autoclave or oven may require multiple calibrated thermocouples, a calibrated temperature data logger, and a calibrated pressure gauge or transducer.

Performance Qualification (PQ)

PQ verifies that equipment consistently produces product meeting specification under actual production conditions. PQ uses production materials, production settings, and production operators. All measurement instruments used in PQ must have SAC-SINGLAS accredited calibration certificates (or equivalent ISO/IEC 17025 accredited certificates). Any instrument found out-of-tolerance during PQ requires immediate investigation and potential re-execution of the affected PQ runs.

Medical Device Calibration Summary

Qualifying Your Calibration Supplier Under Clause 7.4

ISO 13485 Clause 7.4 (Purchasing) requires that suppliers of processes affecting product quality, including calibration services, be evaluated and selected based on their ability to supply product that meets requirements. A calibration laboratory is a critical supplier, and HSA GMP inspectors regularly ask manufacturers to show evidence of supplier qualification for the calibration lab, not just the calibration certificates themselves.

What supplier qualification should cover

A defensible calibration supplier qualification file typically includes: a copy of the laboratory's current SAC-SINGLAS accreditation certificate and scope of accreditation (confirming the specific parameters and ranges the lab is accredited to calibrate); confirmation that the scope covers every parameter the manufacturer sends for calibration; a record of when the qualification was performed and by whom; and a periodic review cycle (commonly annual) to confirm the accreditation remains current and has not lapsed or been narrowed. Manufacturers who send instruments outside a lab's accredited scope, then present the resulting certificate as accredited evidence, create a finding that inspectors catch quickly by cross-checking the scope document against the certificate.

Multiple calibration suppliers

Larger manufacturing sites in Singapore often use more than one calibration laboratory, split by parameter specialism (electrical, dimensional, temperature, force). Each supplier requires its own qualification record. A common audit gap is a manufacturer with a well-documented qualification for their primary lab but no equivalent record for a secondary lab used for an occasional or specialist parameter. The Clause 7.4 requirement applies equally regardless of calibration volume.

Common GMP Audit Findings in Calibration Systems, and How to Prevent Them

Across HSA inspections and third-party ISO 13485 audits of Singapore medical device manufacturers, a small number of calibration-related findings recur with enough frequency that they are worth addressing proactively rather than discovering them during an inspection.

• Missing measurement uncertainty on certificates used for validation. A certificate that reports only pass/fail or raw readings without a stated uncertainty does not meet Clause 7.6 intent and is a frequent finding, particularly on older certificates or instruments calibrated by non-accredited providers before a supplier switch.
• Calibration register out of sync with the physical instrument inventory. New instruments purchased and put into service without being added to the calibration register are found "in production, uncalibrated" during floor walks, a serious finding because it suggests the control system itself has a gap rather than an isolated lapse.
• Overdue calibration with no compensating control. An instrument past its due date that continued to be used in production without a documented risk assessment or interim verification is treated as equivalent to an OOT finding by most auditors, even if the instrument turns out to still be within tolerance when eventually recalibrated.
• Calibration scope mismatch. Sending a pressure gauge to a lab accredited only for electrical parameters, then filing the resulting certificate as if it were accredited evidence, is caught by cross-referencing the lab's published scope against the parameter calibrated.
• Incomplete OOT investigation closure. Investigations opened but not formally closed with a documented disposition decision and corrective action leave the quality system exposed during an audit, even where the underlying risk was genuinely low.

Each of these findings is preventable with a calibration register that is actively maintained (not just created once and left static), and a supplier relationship with a lab, such as Unitest Instruments, that proactively flags scope limitations and provides complete as-found/as-left data with every certificate as standard practice rather than on request.

Building a Calibration Master Schedule That Survives an Audit

A calibration master schedule is the single document most HSA inspectors and third-party auditors ask to see first when reviewing a medical device manufacturer's calibration system. It is the register that ties every instrument to its due date, its owner, and its status, and a schedule that is incomplete or inconsistent with what is physically on the production floor undermines confidence in the rest of the quality system, even where individual certificates are technically correct.

A workable master schedule identifies each instrument by a unique asset number, records its location, its calibration interval and the basis for that interval (manufacturer recommendation, historical drift data, or risk-based justification), its last and next calibration dates, and its accredited status. For manufacturers running more than a handful of instruments, a spreadsheet quickly becomes error-prone; many Singapore facilities move to a dedicated calibration management system once the instrument count passes roughly fifty units, specifically to automate due-date alerts and prevent instruments quietly running past their interval unnoticed. Whichever system is used, the schedule should be reconciled against the physical instrument inventory at least annually, closing the most common gap auditors find: instruments in active use that were never added to the register in the first place.