How is PEM diagnosed?

December 27, 2025 •

3 min read

According to the World Health Organization, malnutrition remains a global health problem that can affect anyone, but the term 'PEM' can also refer to a debilitating symptom in Myalgic Encephalomyelitis (ME/CFS). Diagnosing PEM accurately depends on which condition is being investigated.

Quick Summary

The diagnosis for PEM depends on whether it refers to Protein-Energy Malnutrition or Post-Exertional Malaise associated with ME/CFS. Methods range from anthropometric measurements and blood tests for malnutrition to clinical history, symptom questionnaires, and two-day exercise testing for ME/CFS.

Key Points

Acronym Ambiguity: PEM can mean either Protein-Energy Malnutrition or Post-Exertional Malaise; the diagnostic approach differs significantly for each.
Diagnosing Malnutrition: Protein-Energy Malnutrition is diagnosed using a blend of dietary history, physical exams, anthropometric measurements like BMI, and lab tests for protein and nutrient deficiencies.
Diagnosing ME/CFS PEM: Post-Exertional Malaise is diagnosed based on a clinical history of symptom worsening following exertion, often supported by symptom questionnaires.
Objective Testing for ME/CFS: A two-day Cardiopulmonary Exercise Test (CPET) can provide objective evidence of PEM but carries the risk of triggering a severe relapse.
Clinical Evaluation is Key: Given the lack of a definitive biomarker for ME/CFS-related PEM, a thorough medical history and the exclusion of other fatiguing illnesses are essential parts of the diagnostic process.
GLIM Criteria for Malnutrition: For adults, the Global Leadership Initiative on Malnutrition (GLIM) provides specific phenotypic and etiological criteria for diagnosing and grading Protein-Energy Malnutrition.

The acronym PEM can refer to two very different medical conditions: Protein-Energy Malnutrition or Post-Exertional Malaise, a hallmark symptom of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Due to this ambiguity, a correct diagnosis hinges on a comprehensive medical assessment tailored to the suspected underlying issue.

Diagnosing Protein-Energy Malnutrition (PEM)

Protein-Energy Malnutrition (PEM) is diagnosed through a combination of methods including dietary history, physical examination, and laboratory tests to assess the extent and severity of the deficiency.

Diagnostic Approaches for Protein-Energy Malnutrition

History and Physical Examination: Healthcare providers evaluate a patient's dietary habits, recent weight changes, and any conditions affecting nutrient absorption or increasing metabolic needs. The physical exam looks for signs such as severe muscle wasting and loss of fat (marasmus) or swelling and skin/hair changes (kwashiorkor).
Anthropometric Measurements: Objective body measurements are used to quantify malnutrition. This includes height, weight, BMI, and mid-upper arm circumference (MUAC).
Laboratory Tests: Blood tests provide insight into nutritional status. Key tests include serum albumin and prealbumin for protein levels, complete blood count for anemia, electrolyte levels for imbalances, and micronutrient levels for specific deficiencies.

Global Leadership Initiative on Malnutrition (GLIM) Criteria

For adults, the GLIM criteria offer a standardized, two-step approach for diagnosing malnutrition. This requires at least one phenotypic criterion (weight loss, low BMI, or reduced muscle mass) and at least one etiological criterion (reduced food intake/assimilation or disease/inflammation).

Diagnosing Post-Exertional Malaise (PEM)

Diagnosing Post-Exertional Malaise (PEM), a core symptom of ME/CFS, primarily relies on clinical history and symptom patterns, as specific biomarkers are lacking. Distinguishing PEM from normal fatigue involves observing a delayed and disproportionate worsening of symptoms after even minimal exertion.

Assessment for PEM in ME/CFS

Symptom History: Doctors ask detailed questions about a patient's response to exertion, including triggers (physical, cognitive, emotional), the nature and timing of the post-exertional crash (often delayed by 12-48 hours), and the duration and severity of resulting symptoms.
Symptom Questionnaires: Tools like the DePaul Symptom Questionnaire (DSQ) help assess the frequency and severity of ME/CFS symptoms, including a specific subscale for PEM.
Activity Tracking: Encouraging patients to log activities, triggers, and symptoms can help identify patterns of PEM over time.
Cardiopulmonary Exercise Test (CPET): A two-day CPET can offer objective evidence of PEM by measuring exercise response. A significant decline in performance on the second day is often seen in ME/CFS patients. However, this test must be used with caution due to the risk of inducing a severe crash.

Comparison of Diagnostic Methods for PEM


Feature	Protein-Energy Malnutrition (PEM)	Post-Exertional Malaise (PEM)
Associated Condition	A severe nutritional deficiency	A hallmark symptom of ME/CFS and Long COVID
Primary Diagnostic Basis	Physical exam, anthropometrics, and lab tests	Detailed clinical history and symptom pattern
Objective Measurements	Weight, height, BMI, MUAC, serum albumin, electrolytes	Two-day Cardiopulmonary Exercise Test (CPET)
Subjective Assessment	Dietary history, medical history	Symptom questionnaires (e.g., DSQ), activity logs
Key Laboratory Findings	Anemia, low albumin, electrolyte imbalances	No specific lab test; lab tests are used to rule out other conditions
Risk of Diagnostic Tool	Refeeding syndrome during treatment	Provoking a severe and prolonged crash during CPET

Conclusion

Diagnosing PEM requires understanding whether it refers to protein-energy malnutrition or post-exertional malaise in the context of ME/CFS or Long COVID. Protein-energy malnutrition is diagnosed using physical and laboratory data, often guided by criteria like GLIM. Post-exertional malaise is primarily a clinical diagnosis based on symptom history and response to activity, potentially supported by questionnaires and objective tests like the two-day CPET, though the latter must be used cautiously due to the risk of symptom aggravation. A thorough medical evaluation is essential for accurate diagnosis and management of either condition. Learn more about post-exertional malaise from the CDC(https://www.cdc.gov/me-cfs/hcp/clinical-care/treating-the-most-disruptive-symptoms-first-and-preventing-worsening-of-symptoms.html).

Frequently Asked Questions

Protein-Energy Malnutrition (PEM) is a nutritional deficiency caused by insufficient caloric and protein intake, while Post-Exertional Malaise (PEM) is a debilitating symptom of ME/CFS characterized by a disproportionate worsening of symptoms after minimal exertion.

Yes, common blood tests for Protein-Energy Malnutrition include checking levels of serum albumin, prealbumin, electrolytes, and performing a complete blood count to look for anemia. These tests help assess the severity of malnutrition and identify related complications.

The two-day Cardiopulmonary Exercise Test (CPET) is a procedure where a patient performs an exercise test on two consecutive days. A significant drop in performance on the second day is objective evidence of Post-Exertional Malaise, which distinguishes ME/CFS patients from healthy individuals or those with other fatiguing illnesses.

Yes, for Post-Exertional Malaise, standardized questionnaires such as the DePaul Symptom Questionnaire (DSQ) are valuable tools. They help clinicians assess the frequency, severity, and specific nature of a patient's PEM experiences.

The primary risk is that the exertion involved in the test can trigger a severe and prolonged crash or relapse in ME/CFS patients, worsening their condition for days or weeks.

In children, diagnosis of Protein-Energy Malnutrition involves assessing growth patterns using charts, measuring height and weight to calculate Z-scores, and performing a physical examination to check for signs of marasmus or kwashiorkor.

Clinical history is paramount in diagnosing Post-Exertional Malaise, as it helps identify the key pattern of symptoms worsening after exertion. Doctors rely on patient reports to understand triggers, the delayed onset, and the duration of post-exertional crashes.