WHO Does Not Define "Acute-on-Chronic Malnutrition" as a Distinct Diagnostic Category
The WHO does not recognize "acute-on-chronic malnutrition" as a formal diagnostic entity. Instead, the current international classification systems, including those endorsed by ESPEN (European Society for Clinical Nutrition and Metabolism), categorize malnutrition based on etiology and inflammatory status, not on temporal patterns of acute versus chronic onset 1.
Current International Classification Framework
The established taxonomy divides malnutrition into three main etiological categories 1:
Disease-related malnutrition (DRM) with inflammation, which subdivides into:
DRM without inflammation (non-cachectic DRM) - caused by mechanisms like dysphagia, malabsorption, or neurologic disorders without inflammatory component 1
Malnutrition without disease - including hunger-related and socioeconomic/psychological malnutrition 1
Why the Term "Acute-on-Chronic" Is Not Used
The current framework explicitly distinguishes between chronic and acute forms as separate entities rather than overlapping conditions 1. The ESPEN guidelines emphasize that inflammation serves as the critical watershed for classification, not the temporal sequence of malnutrition development 1.
Key Distinctions in Practice:
Chronic DRM with inflammation (cachexia) occurs in end-stage organ diseases (cancer, COPD, heart failure, chronic kidney disease) with ongoing but milder inflammation 1
Acute disease- or injury-related malnutrition presents in ICU patients with major infections, burns, trauma, or post-surgical states with pronounced stress metabolism and high pro-inflammatory cytokine activity 1
Clinical Implications
When encountering a patient with pre-existing chronic malnutrition who develops an acute illness, classify based on the current dominant pathophysiology 1. For example:
A patient with cancer cachexia (chronic DRM with inflammation) who develops sepsis should be managed as having acute disease-related malnutrition with the understanding that baseline nutritional status was already compromised 1
The diagnostic criteria remain the same regardless of temporal pattern: BMI thresholds, weight loss percentages, reduced muscle mass, combined with evidence of inflammation 1
Common Pitfall to Avoid
Do not attempt to use "acute-on-chronic" terminology in formal documentation or treatment planning, as it lacks standardized diagnostic criteria and is not recognized in international guidelines 1. Instead, identify the specific etiological category and inflammatory status, which directly guides nutritional intervention strategies 1.
The absence of this term reflects the evidence-based understanding that malnutrition classification should be driven by underlying pathophysiology and inflammatory markers rather than temporal descriptors 1.