Validation of Fatty Liver Index and Hepatic Steatosis Index for Screening of Non-Alcoholic Fatty Liver Disease in Adults with Obstructive Sleep Apnea Hypopnea Syndrome
Obstructive sleep apnea hypopnea syndrome (OSAHS) – a condition where the upper airway repeatedly blocks during sleep, causing drops in oxygen levels – affects 2–4% of the general population but jumps to 35–45% in people with obesity. What many don’t know is that OSAHS is tightly linked to non-alcoholic fatty liver disease (NAFLD), a common liver condition where fat builds up in the liver without heavy alcohol use. NAFLD is now the leading cause of chronic liver disease worldwide, and OSAHS patients are at especially high risk due to their links to obesity, insulin resistance, and inflammation.
Screening for NAFLD usually requires invasive liver biopsies or expensive imaging, which aren’t practical for routine care. That’s why researchers have been testing simple, non-invasive tools like the Fatty Liver Index (FLI) and Hepatic Steatosis Index (HSI) – indexes that use routine measurements (like weight, waist size, and blood tests) to predict liver fat. But do these tools work for OSAHS patients, who face unique metabolic and sleep-related risks? A 2019 study from Chinese researchers aimed to find out.
What the Study Did
The research team, led by Li-Da Chen from Fujian Medical University’s affiliated hospitals, enrolled 431 adults newly diagnosed with OSAHS between 2016 and 2018. Participants came from two sleep labs in Fujian Province, China, and were diagnosed with OSAHS using polysomnography (PSG) – a gold-standard sleep test that tracks breathing, oxygen levels, and brain activity.
To ensure accuracy, researchers excluded anyone with:
- Excessive alcohol use (more than 20g/day for men, 10g/day for women)
- Viral hepatitis (B or C)
- Autoimmune or drug-induced liver disease
- Prior OSAHS treatment (like CPAP)
For each participant, the team measured:
- Anthropometrics: Height, weight (to calculate BMI), waist circumference, neck circumference
- Blood tests: Fasting glucose, liver enzymes (ALT, AST, GGT), and lipids (cholesterol, triglycerides)
- Sleep metrics: Apnea-hypopnea index (AHI, number of airway blocks per hour), oxygen desaturation index (ODI), lowest oxygen level (LaSO2), and time spent with oxygen <90% (T90%)
NAFLD was diagnosed using abdominal ultrasound – a common, non-invasive test that detects liver fat by measuring echo intensity (how sound waves bounce off the liver).
What They Found
Of the 431 participants, 326 had NAFLD (75% of the group) and 105 had normal liver ultrasounds. Here’s what stood out:
1. NAFLD Patients Had Worse Metabolic and Sleep Health
People with NAFLD were more likely to have:
- Higher BMI, waist circumference, and neck circumference (key markers of obesity)
- Worse sleep quality: Higher AHI (more airway blocks), higher ODI (more oxygen drops), and more time spent with low oxygen (T90%)
- Unhealthier blood work: Higher glucose, triglycerides, cholesterol, and liver enzymes (signs of metabolic stress and liver damage)
2. FLI and HSI Were Higher in NAFLD Patients
Both indexes were significantly higher in people with NAFLD:
- FLI: Median 73 vs. 44 in non-NAFLD patients
- HSI: Median 40 vs. 35 in non-NAFLD patients
3. FLI Performed Better Than HSI
To test how well each index predicted NAFLD, researchers used receiver operating characteristic (ROC) curves – a tool that measures a test’s ability to distinguish between people with and without a condition. The area under the curve (AUROC) ranges from 0 (no ability) to 1 (perfect ability).
- FLI: AUROC = 0.802 (95% confidence interval [CI] 0.762–0.839)
- HSI: AUROC = 0.753 (95% CI 0.710–0.793)
FLI’s AUROC was significantly higher than HSI’s (p = 0.038), meaning it was better at identifying NAFLD in OSAHS patients.
4. Optimal Cutoff Values
The team calculated the best “cutoff” scores for each index – values where sensitivity (ability to catch true NAFLD cases) and specificity (ability to rule out non-NAFLD cases) were balanced:
- FLI: A cutoff of 60 correctly identified 66% of NAFLD cases (sensitivity) and 80% of non-NAFLD cases (specificity).
- HSI: A cutoff of 35 correctly identified 81% of NAFLD cases but only 60% of non-NAFLD cases.
What This Means for OSAHS Patients
This study adds strong evidence that both FLI and HSI are useful screening tools for NAFLD in OSAHS patients – a group at high risk for liver disease. But FLI is the better choice: it’s more accurate at distinguishing between people with and without NAFLD.
Why FLI and HSI Matter
Unlike liver biopsies (which are invasive, expensive, and carry risks), FLI and HSI use routine, low-cost measurements that most clinics already collect. For OSAHS patients – who often have comorbidities like obesity and diabetes – these indexes offer a quick, easy way to flag NAFLD early, before liver damage progresses.
How to Use the Cutoffs
- FLI ≥60: High chance of NAFLD (80% specificity). If an OSAHS patient scores 60 or higher, they should get further testing (like a liver ultrasound or FibroScan) to confirm NAFLD.
- HSI ≥35: Moderate chance of NAFLD (81% sensitivity). While less specific, it’s good for “ruling in” NAFLD – if a patient scores below 35, NAFLD is unlikely.
Limitations to Consider
No study is perfect. Here are key caveats:
- No Liver Biopsy: The gold standard for NAFLD is a liver biopsy, which can measure fat percentage and fibrosis (scarring). Ultrasound – used here – misses mild steatosis (less than 20–30% fat) in some cases.
- Small Sample: The study included 431 patients, which is smaller than some population-wide studies. Results may not apply to all OSAHS patients (e.g., those with milder OSAHS or different ethnicities).
- Ultrasound Variability: Ultrasounds were done by multiple technicians, which can lead to differences in how fatty liver is diagnosed.
The Takeaway
For OSAHS patients – a group already at high risk for metabolic and liver disease – FLI and HSI are valuable tools to screen for NAFLD. FLI is more accurate, but both can help clinicians identify who needs further testing.
The study also highlights a critical point: OSAHS and NAFLD are not separate conditions – they’re linked through obesity, inflammation, and sleep-related hypoxia. If you have OSAHS, talking to your doctor about NAFLD screening (using tools like FLI) could help catch liver disease early, when lifestyle changes (like weight loss, diet, or CPAP therapy) can make a big difference.
This study was published in the Chinese Medical Journal in 2019. The original research was registered with the Chinese Clinical Trial Registry (No. ChiCTR-OOB-15007253).
https://doi.org/10.1097/CM9.0000000000000503
Was this helpful?
0 / 0