What is MASH and Required Workup
MASH (metabolic dysfunction-associated steatohepatitis) is the inflammatory and progressive form of metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD), characterized by hepatic steatosis, lobular inflammation, and hepatocyte ballooning that leads to fibrosis, cirrhosis, and hepatocellular carcinoma if untreated 1.
Definition and Disease Spectrum
MASH sits within the MASLD spectrum, which includes:
- Simple steatosis (fat accumulation alone)
- MASH (steatosis + inflammation + ballooning)
- Progressive fibrosis (stages F0-F4)
- Cirrhosis
- Hepatocellular carcinoma
The key distinction: MASLD requires hepatic steatosis plus at least one cardiometabolic risk factor (obesity, type 2 diabetes, hypertension, dyslipidemia, metabolic syndrome) with no harmful alcohol intake (≤20 g/day in women, ≤30 g/day in men) 1.
Required Workup: A Stepwise Fibrosis-Focused Approach
The critical clinical task is not simply detecting steatosis but identifying clinically significant fibrosis (≥F2), which predicts liver-related morbidity and mortality 2.
Step 1: Case-Finding (Who to Evaluate)
Apply case-finding strategies in:
- Type 2 diabetes (highest priority group)
- Obesity with additional metabolic risk factors
- Unexplained elevated liver enzymes (ALT, AST)
- Incidental hepatic steatosis on imaging 1
Step 2: Initial Assessment
A. Confirm steatosis:
- Ultrasound, CT, or MRI showing hepatic steatosis
- Or liver biopsy (rarely needed initially)
B. Define metabolic context - document presence of:
- Body mass index and waist circumference
- Type 2 diabetes or impaired glucose tolerance
- Hypertension
- Dyslipidemia (elevated triglycerides, low HDL)
- Metabolic syndrome components
C. Quantify alcohol exposure:
- Detailed history: quantity, pattern, type
- Use validated questionnaires (AUDIT-C)
- Consider biomarkers if history unreliable
- Critical thresholds: >20 g/day (women) or >30 g/day (men) suggests alternative diagnosis 1
D. Exclude competing liver diseases:
- Viral hepatitis (HBsAg, anti-HCV)
- Autoimmune hepatitis (ANA, ASMA, immunoglobulins)
- Hemochromatosis (ferritin, transferrin saturation)
- Wilson disease (ceruloplasmin if age <40)
- Alpha-1 antitrypsin deficiency
- Celiac disease
- Drug-induced liver injury (medication review) 1
Step 3: Fibrosis Risk Stratification (Sequential Noninvasive Testing)
This is the most important part of the workup - fibrosis stage determines prognosis and treatment eligibility.
A. First-line blood-based score: FIB-4
Calculate FIB-4 = (Age × AST) / (Platelet count × √ALT)
Interpretation:
- FIB-4 <1.3: Low risk of advanced fibrosis - routine follow-up, lifestyle modification
- FIB-4 1.3-2.67: Indeterminate - proceed to Step B
- FIB-4 >2.67: High risk of advanced fibrosis - proceed to Step B 1
Common pitfall: FIB-4 has age-dependent performance; use lower cutoffs in younger patients (<35 years: <1.0) and higher in older patients (>65 years: <2.0).
B. Second-line imaging: Transient Elastography (FibroScan)
Measure liver stiffness (kPa):
- <8 kPa: Rules out advanced fibrosis
- 8-12 kPa: Indeterminate, consider additional testing
- >12 kPa: Suggests advanced fibrosis (≥F3)
- >15-20 kPa: Suggests cirrhosis 1
Alternative imaging modalities:
- MR elastography (more accurate but less accessible)
- Shear wave elastography
- Acoustic radiation force impulse imaging
C. Consider additional blood-based tests if available:
- Enhanced Liver Fibrosis (ELF) score
- FibroTest
- Pro-C3
- NAFLD Fibrosis Score
Step 4: Determine Need for Liver Biopsy
Biopsy is not routinely required but consider when:
- Noninvasive tests are discordant or indeterminate
- Competing etiologies cannot be excluded
- Patient is candidate for clinical trial
- Confirming MASH diagnosis before starting liver-directed therapy (though increasingly not required with approval of resmetirom) 1
Histologic criteria for MASH:
- Steatosis (≥5% hepatocytes)
- Lobular inflammation
- Hepatocyte ballooning
- Fibrosis staging (F0-F4)
Step 5: Assess Cardiometabolic Comorbidities
Mandatory evaluations:
- Fasting glucose, HbA1c (diabetes screening)
- Lipid panel (cardiovascular risk)
- Blood pressure
- Cardiovascular risk assessment (10-year ASCVD risk)
- Renal function (creatinine, eGFR) - chronic kidney disease is common
- Screen for obstructive sleep apnea if obese 1
Step 6: Surveillance if Advanced Fibrosis/Cirrhosis
For F3-F4 fibrosis or cirrhosis:
- Hepatocellular carcinoma surveillance: Ultrasound + AFP every 6 months 3
- Varices screening: Upper endoscopy if cirrhosis confirmed
- Monitor for decompensation: Ascites, encephalopathy, variceal bleeding 1
Key Clinical Pearls
Pitfall #1: Normal ALT does not exclude MASH or advanced fibrosis. Many patients with significant disease have normal transaminases 2.
Pitfall #2: Do not rely on imaging alone to diagnose MASH - steatosis on ultrasound only confirms MASLD, not the inflammatory MASH component. Fibrosis assessment is essential 1.
Pitfall #3: The stepwise approach (FIB-4 → elastography) is cost-effective and avoids unnecessary specialist referrals for low-risk patients. Reserve hepatology referral for FIB-4 >1.3 or liver stiffness >8 kPa 1.
Pitfall #4: MASH prevalence is 1-6% in the US but rising rapidly with obesity epidemic. Type 2 diabetes patients have highest risk and should be systematically screened 4.
Treatment Eligibility Determination
Based on workup findings:
- F0-F1 (no/mild fibrosis): Lifestyle modification, treat metabolic comorbidities
- F2-F3 (significant fibrosis, non-cirrhotic): Consider resmetirom (FDA-approved 2024) + lifestyle + metabolic optimization 1, 5
- F4 (cirrhosis): No approved MASH-specific therapy; focus on metabolic management, surveillance, transplant evaluation if decompensated 1
GLP-1 receptor agonists (semaglutide, tirzepatide) show benefit for weight loss and metabolic improvement in MASLD/MASH patients with diabetes or obesity 1, 6.