Subjective Global Assessment for Malnutrition Evaluation
Use the Subjective Global Assessment (SGA) as a validated, bedside clinical tool to diagnose malnutrition and identify patients who will benefit from nutritional intervention—it predicts morbidity, mortality, and hospitalization better than objective laboratory markers alone. 1
What SGA Actually Measures
SGA is a structured clinical assessment combining medical history and physical examination to provide a global rating of protein-energy nutritional status. 1 The tool was originally developed for surgical patients but has been validated across multiple populations including dialysis patients, critically ill patients, cancer patients, and pediatric populations. 1, 2, 3
Core Components of the Assessment
The SGA evaluates five historical parameters and three physical examination findings:
Historical Parameters:
- Weight change pattern: Assess both magnitude and timing of weight loss over the past 6 months, with particular attention to losses >10% of usual body weight 1, 4
- Dietary intake changes: Document duration and severity of reduced intake, especially reductions lasting >7-10 days 4, 5
- Gastrointestinal symptoms: Evaluate presence of anorexia, nausea, vomiting, or diarrhea affecting intake 1, 6
- Functional capacity: Assess changes in activity level and whether the patient is bedridden or ambulatory 1, 6
- Metabolic stress: Consider the severity of underlying disease and its impact on nutritional requirements 1, 6
Physical Examination Findings:
- Subcutaneous fat loss: Examine triceps, chest wall, and orbital regions 1, 6
- Muscle wasting: Assess temples, clavicles, shoulders, interosseous muscles, scapula, quadriceps, and calf 1, 6
- Edema: Document presence of ankle, sacral, or ascites 1, 6
Recommended Scoring System
Use the modified 4-item, 7-point scale from the CANUSA study rather than the original 3-point ordinal scale, as it provides greater sensitivity and predictive power for clinical outcomes. 1 This modified approach assigns scores to four key items: weight loss, anorexia, subcutaneous fat, and muscle mass, with ratings from 1-2 (severe malnutrition), 3-5 (moderate to mild malnutrition), to 6-7 (normal nutrition). 1
The traditional SGA classification uses three categories:
Clinical Outcomes and Predictive Value
Higher SGA scores are independently associated with lower mortality risk and fewer hospitalized days per year, with changes in SGA scores correlating directly with clinical outcomes. 1 In the CANUSA study of 680 peritoneal dialysis patients, multivariable analysis demonstrated that SGA predicted both mortality and hospitalization rates. 1
In surgical populations, SGA identifies patients at 44% risk of malnutrition in major abdominal surgery, compared to 20% in chest surgery and 14% in general surgery. 1 Patients identified as malnourished by SGA develop more complications (30.6% vs 11.3%), have higher mortality (12% vs 1%), and experience longer hospital stays (median 9 vs 6 days). 1
SGA has been validated as a reliable tool for identifying malnutrition in mechanically ventilated patients with obesity, demonstrating good prognostic assessment capability. 1
Key Advantages of SGA
- Inexpensive and rapid: Can be performed at bedside in 3-5 minutes 1
- Requires minimal training: Brief instruction allows consistent application 1
- No equipment needed: Based entirely on history and physical examination 1
- Patient or family-reported: Feasible even when patients cannot provide detailed history themselves 4, 1
- Predicts clinical outcomes: Validated for morbidity, mortality, and complication risk across multiple populations 1, 2, 3
Critical Limitations to Recognize
SGA does not include visceral protein levels (albumin, prealbumin, transferrin) in its assessment, focusing instead on nutrient intake and body composition. 1 This is actually appropriate, as albumin and prealbumin are negative acute phase reactants that decrease during inflammation regardless of nutritional status, making them unreliable malnutrition markers in acute illness. 7
SGA may not detect early or mild malnutrition with sufficient sensitivity, and its precision and reproducibility over time have not been extensively studied in all populations. 1, 2 The tool's reproducibility depends heavily on the experience of the clinician administering it. 2
SGA cannot distinguish between malnutrition, cachexia, and sarcopenia—conditions that differ in their mechanisms of body wasting and response to nutritional intervention. 3 A revised SGA form has been developed to help differentiate malnutrition (which responds to nutrition intervention) from these other wasting conditions. 3
In patients with obesity, excess adiposity may present barriers to accurately assessing muscle wasting or fat loss during physical examination. 1 However, SGA has been shown to reliably identify malnutrition even in overweight and obese patients requiring mechanical ventilation. 1
Practical Implementation Algorithm
Step 1: Screen all patients at hospital admission using SGA or validated screening tools (NRS-2002, MUST, MST). 5 The European Society for Clinical Nutrition and Metabolism recommends a two-step approach: systematic screening followed by comprehensive assessment. 5
Step 2: Perform comprehensive SGA assessment on all patients identified as at-risk during screening. 5 This should occur immediately after diagnosis and periodically during the disease course. 1
Step 3: Assign overall SGA rating by synthesizing all historical and physical examination components in context with each other. 6 Do not simply add scores mechanically—use clinical judgment to weigh the relative importance of findings. 3, 6
Step 4: Use SGA diagnosis to guide nutritional intervention decisions, recognizing that SGA identifies patients likely to benefit from nutrition support. 3, 8 Patients with SGA-B or SGA-C ratings require nutritional intervention. 1
Step 5: Reassess SGA scores periodically to monitor response to intervention, as changes in SGA correlate with clinical outcomes. 1
Common Pitfalls to Avoid
Do not confuse suboptimal diet with low BMI alone—SGA dietary assessment focuses on change in intake and recent patterns, not just current body weight. 4 The tool evaluates inadequate protein, micronutrients, and overall dietary diversity that fails to meet metabolic demands. 4
Never use SGA in isolation to evaluate nutritional status—combine it with anthropometric measurements, laboratory evaluation, and functional assessment as independent measures. 1, 7 The National Kidney Foundation guidelines explicitly state that nutritional assessment should include multiple independent parameters. 1
Do not rely solely on objective measurements like BMI, midarm circumference, or tissue skinfold thickness, as these may not correlate with postoperative complication risk as well as SGA does. 7
Avoid interpreting SGA results without considering the patient's inflammatory status and underlying disease severity. 7 In critically ill patients or those with significant inflammation, body composition changes may reflect disease processes rather than pure malnutrition. 7
Do not wait for laboratory confirmation to begin nutritional support if SGA identifies malnutrition—clinical signs warrant immediate intervention. 7
Enhanced Scoring Systems
Modified quantitative SGA (MQ-SGA) systems that assign weighted scores to individual SGA items show superior specificity (85.6%) compared to simple quantitative scoring (67.0%), while maintaining similar sensitivity (90.9% vs 90.0%). 9 These weighted systems account for the differential impact of various SGA components on malnutrition diagnosis. 9
Integration with Other Assessment Tools
Combine SGA with the Nutrition-Focused Physical Exam (NFPE) for comprehensive assessment, particularly in patients with obesity where excess adiposity may mask muscle wasting. 1 The NFPE systematically evaluates general appearance, body habitus compared to usual weight, and hands-on assessment of fat mass, muscle mass, edema, and micronutrient deficiency signs. 1
Use SGA alongside laboratory markers (albumin, prealbumin, absolute lymphocyte count) and C-reactive protein to distinguish inflammatory effects from true nutritional depletion. 7 This combination accurately predicts postoperative complications after abdominal surgery. 7
Pediatric Considerations
Adapted pediatric SGA tools have been validated for children undergoing surgery, demonstrating ability to identify nutritional status and predict nutrition-associated complications postoperatively. 6 Age-related questionnaires guide history taking for growth, weight changes, dietary intake, gastrointestinal symptoms, functional capacity, and metabolic stress in infants, children, and adolescents. 6
Adoption and Sustainability
Initial hesitancy among clinicians to use SGA transforms into recognition of improved clinical practice after implementation and experience. 8 Dietitians report that SGA allows them to "see the right people, sooner," improves overall efficiency in care delivery, and makes them "better clinicians." 8 Establishing clear policies and procedures supports sustained use of SGA in routine practice. 8