What is the difference between IVDR Class D and C?

by Harry Mingay and Dr. Rita Hendricusdottir on 30 Jun 2022

Reading time: 3 minutes

This blog post will discuss ways in which high personal and public health risks for In Vitro Diagnostics (IVD) devices are determined – and introduce some of the classification issues that can arise because of this.

With IVD devices, false positive or false negative results for life-threatening, transmissible diseases can endanger both the patient, as well as the wider public. This means that both personal and public health risks need to be considered to determine the classification of IVD devices. The COVID-19 pandemic provides a suitable example to demonstrate this point. At the early stages of the COVID-19 pandemic, individuals with a positive COVID-19 test needed to (self-)isolate. So, if an individual is infected with COVID-19 and a negative antigen test was obtained, then it is not only the individual in question that is at risk. The person would not need to isolate, which subsequently endangers everyone who comes into close contact with this individual.

Both Class C and Class D IVD devices relate to diseases, conditions, and patient management decisions with a high personal health risk. Where they differ is on the risk they pose to public health. The most significant difference between these device groups is that Class D devices refer to those which carry a high public health risk, whereas Class C devices refer to those with a moderate to low public health risk.

Due to the high personal risk element of both device classes, many of the classification rules for Class C and Class D devices refer to life-threatening diseases, conditions, and situations. The Medical Device Coordination Group (MDCG) IVD Device Classification guidance document has provided a definition for this term, which states:

Life threatening refers to ‘diseases, conditions or situations that in general result in death. These are often untreatable, treatment options are limited or require major medical interventions.’

Defining life-threatening as ‘in general result(ing) in death’, indicates that the frequency of death should be considered. The problem with this is that for many diseases, the frequency of death is not known, as it can be confounded by many other health considerations. While ‘life-threatening’ is a term that is widely understood, interpretation issues can arise at the borderline between life-threatening and non-life-threatening diseases, as many diseases that may not be widely considered to be life-threatening can in certain cases result in death. Example of life-threatening diseases is listed in the MDCG’s guidance document, which includes Smallpox, HIV and SARS-CoV-2.

The second important distinction is made with the risk of propagation (transmissibility) of a disease, as this has a direct implication as to whether a false negative could endanger the wider public health. Several factors have been identified by the MDCG that contribute towards the risk of propagation, which are noted below.

‘(1) The direct or in-direct transmissibility (i.e. the probability of infection when there is contact between a susceptible and an infected individual). This includes for example consideration of the infectious dose and route of transmission e.g. aerosol, zoonosis, vector-mediated. (2) The contact rate of infected and susceptible individuals (i.e. the number of contacts per time). (3) The duration of infectiousness’

However, no information is given as to exactly where the classification boundaries are for these factors. When determining if a disease has a suspected high risk of propagation then these three factors should be taken into account, yet they have the potential to be interpreted differently amongst medical device manufacturers. Example diseases that have a suspected high risk of propagation are listed in the MDCG’s guidance document include Hepatitis B/C/D, HIV 1/2, and SARS CoV/CoV-2. Infectious agents without a suspected high risk of propagation listed in the MDCG’s Guidance document and include Group B Streptococcus, Hepatitis A/E, Dengue, Zika, Herpes simplex virus 1/2, and Toxoplasma gondii.


The new rule-based classification of IVD devices that has replaced the current list-based approach marks a major change in how IVD devices are regulated. This change does allow the legislation to stay up-to-date as novel IVD devices are invented. However, it requires a greater understanding of the regulation for IVD device manufacturers, as misclassifying a device submitted for a conformity assessment could be a costly mistake. Borderline cases for these two distinctions will become more apparent with time, as more device-specific classifications will be published as the IVDR is applied. It is suggested that IVD device manufacturers should contact their notified body/relevant regulatory authority if the guidance documents are not sufficient to distinguish between two (or more) different classifications for their device.