Nicolette de Keizer researches the role  of medical registries, audit programs and other healthcare ICT systems in improving the quality of healthcare. Most research is within the context of the National Intensive Care Evaluation (NICE) registration. The focus of her work includes developing quality indicators, prognostic models and evaluating audit and feedback on quality improvements, for which she collaborates closely with various intensive care wards, including that of the AMC-UvA.

De Keizer is also conducting research into SNOMED CT, a clinical terminology system based on formal logic for storing medical information in a detailed and standardised manner in electronic patient records. According to De Keizer, standardisation using information models and terminology systems is an absolutely key condition for reusing data from existing healthcare information systems, for example in order to measure and improve the quality of healthcare.

As a lecturer, De Keizer teaches in both the Bachelor's and Master's programmes in Medical Informatics. As head of the Health Informatics programme, she has led a team of lecturers working on the development of a new advanced Master's curriculum since 2014. A fully e-learning based programme, this Master's targets healthcare professionals who, alongside their regular duties, play an important role in the innovation, selection and structuring of information and communication technology within the healthcare field.

As chair of the International Medical Informatics Association working group for Evaluation Methods, De Keizer has worked on developing standards for conducting and reporting on healthcare ICT evaluation studies. Since 1995 she has filled various positions at the AMC-UvA, in recent years as associate professor and principal investigator in the Medical Informatics department. She has been the recipient of several research grants, including grants from ZonMw and the National Intensive Care Evaluation (NICE) foundation. De Keizer has published extensively in professional journals such as  Critical Care Medicine, International Journal of Medical Informatics and the  British Medical Journal.