Software Safety Classes (IEC 62304) versus Levels of Concern (FDA)

Both, European and US regulations, distinguish three different categories of medical device software, the software safety classes accordingly to IEC 62304 respectively the FDA levels of concern. Frequently manufactures confuse both.

Software safety classes

IEC 62304:2006 + Amendment 2015 define the software safety classes as follows:

Level of Concern

The FDA defines the Levels of Concern as follows:

Please note that both definitions primarily are dependent on the severity of potential harms and not on risks. I.e. the probability of this harms is not what determines the software safety class respectively the level of concern.

2. Goals of classification

The IEC 62304 introduces the software safety classes to determine the extent of documentation to be complied.

Table 1: The documentation depends on the safety class IEC 62304. E.g. for class A software no software architecture (chapter 5.3) is required. The numbers correspond to the chapters of the standard.

The FDA uses the levels of concern to determine the amount of documentation to be submitted. I.e. the level of concern does not influence the documentation to be compiled.

3. Reduction of software safety class respectively level of concern

Reduction of software safety class

IEC 62304 permits a reduction of the software safety class by means that are external to the software only. Examples are:

• Physical hardware e.g. a stopper
• Other component containing hardware (electronics) and even software e.g. a watchdog
• User e.g. responding to a warning (not in IfU) or pressing an emergency stop

Reduction of level of concern

The FDA expects measures to mitigate risks. However, the levels of concern are determined prior to these measures. I.e. a reduction of the level of concern does not impact the documentation to be submitted.

4. Changes: end of the “level of concern”

On November 4, 2021, the FDA published the draft of a guidance document entitled Content of Premarket Submissions for Device Software Functions. This document is intended to replace the guidance document that introduced the level of concern.

This new guidance document only differentiates between two classes.

a) Defining the classes

The FDA no longer defines three “levels of concern.” Instead, it now defines two “documentation levels”:

1.  Basic Documentation Level
2.  Enhanced Documentation Level

Software requires “Enhanced Documentation" if at least one of the following conditions is met: 

This device that contains the software or is the software:

1.  Is a combination product
2.  Is intended for use in transfusion medicine or organ donation (determination of organ donor and recipient compatibility)
3.  Is classified as class III
4.  Can lead to death or serious injury in the event of a fault 

With regard to the fourth point, the FDA refers to reasonably foreseeable risks.

b) Consequence of classification

Like the level of concern, the classification also affects the scope of the (software) documentation to be submitted:

The new requirements are very similar to the previous moderate and major levels. This means that manufacturers cannot submit software documentation that only meets the very lax requirements of the minor level of concern.

c) Evaluation

The FDA makes extensive references to IEC 62304. However, from the publication of the new version of the guidance document at the latest, a procedure as per class A is no longer permitted. In addition, manufacturers should be aware that the amount of documentation to be submitted is independent of the amount of documentation to be created.

The Johner Institute recommends that manufacturers work and create documentation in conformity with the requirements of safety class C.