What is an IVD Quality Control?

IQC vs EQA — what is the difference?

Internal Quality Control (IQC) is performed within the laboratory, typically at the start of each analytical run and at defined intervals throughout the working day. IQC samples are measured by the same method and operator as patient samples — the results are compared to established mean and standard deviation values to detect out-of-control situations before patient results are reported. Failure of IQC triggers investigation and corrective action before the run is accepted.

External Quality Assessment (EQA), also called Proficiency Testing (PT), involves the laboratory receiving blind samples from an external provider, measuring them by their routine method, and submitting results. The EQA provider compares results across all participating laboratories to assess inter-laboratory performance. EQA identifies systematic biases that IQC cannot detect — for example, a calibrator offset that consistently shifts results in one direction while maintaining good precision.

Why does commutability matter?

A QC material is commutable when it behaves identically to native patient samples across different measurement procedures. Non-commutable QC materials (e.g. reconstituted lyophilised controls with additives or stabilisers) can give correct results on one platform but systematically biased results on another — not because the platforms are wrong, but because the matrix of the control reacts differently to different reagent formulations. For multi-platform EQA programmes, commutable native human QC materials are the only format that provides a valid comparison across different analyser systems.

IQC acceptance rules — Westgard

Westgard rules are the standard statistical framework for IQC decision-making. The most commonly applied rules:

• 1₂s: Warning rule — one QC result exceeds ±2 SD. Triggers investigation but does not automatically reject the run
• 1₃s: Rejection rule — one QC result exceeds ±3 SD. Run rejected
• 2₂s: Two consecutive QC results exceed the same ±2 SD limit — systematic error, run rejected
• R₄s: Range between two QC results exceeds 4 SD — random error, run rejected
• 10x: Ten consecutive QC results on the same side of the mean — systematic drift, run rejected

CE-IVD certified controls vs research-grade QC materials

CE-IVD certified quality controls are IVDs in their own right — they bear CE marking and have been through the full IVDR conformity assessment for their intended use as QC materials. Research-grade QC materials are native human biomaterial supplied for laboratory use but without CE-IVD marking. For accredited clinical laboratories under ISO 15189, CE-IVD certified controls are preferred where available. For R&D and assay development, research-grade native human QC materials provide the most relevant matrix at lower cost.

Key Facts

• Two main QC frameworks: Internal Quality Control (IQC) — run within the laboratory every day; External Quality Assessment (EQA) / Proficiency Testing (PT) — blind samples distributed by an external provider for inter-laboratory comparison
• QC materials should ideally be commutable — behaving identically to patient samples across different analytical platforms and methods
• Native human biomaterial QC (produced from real human serum, plasma or other matrices without additives) has maximum commutability — unlike reconstituted lyophilised or spiked controls which can show platform-specific matrix effects
• Westgard rules define the statistical decision criteria for accepting or rejecting an analytical run based on QC result patterns — 1₂s, 1₃s, 2₂s, R₄s, 4₁s, 10x are the most commonly applied
• CE-IVD certified QC materials are available for specific analytes — required when the QC material itself is classified as an IVD under IVDR 2017/746
• ISO 15189 (medical laboratory accreditation) requires documented IQC procedures with defined acceptance criteria for every measurand
• SeamlessBio supplies native human-origin QC materials across autoimmunity, infectiology, endocrinology, gastroenterology, oncology and allergy — CE-certified In.QualiCheck controls for calprotectin and PSA

Further Reading

• Human IVD Quality Controls & Standard Materials
• What is Disease State Serum?
• What is IVDR Class D?
• IVDR Class D Sample Sets
• Human Biomaterials & IVD — Overview

SeamlessBio GmbH · Passau, Germany · info@seamlessbio.de · +49 851 37932226