FibroScan / VCTE: Sex- and Cycle-Related Differences, Normal Ranges, and Optimal Targets

What Is FibroScan / VCTE and Why Does It Matter for MASLD?

FibroScan uses a 50-Hz vibration pulse to generate a shear wave through hepatic tissue; the device measures how fast that wave travels, expressing the result as liver stiffness in kilopascals (kPa). The Controlled Attenuation Parameter (CAP) is captured simultaneously and quantifies hepatic steatosis in dB/m. Together, the two values stage metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD) without a biopsy.

The clinical stakes are significant. MASLD now affects an estimated 38% of the global adult population, based on a 2023 meta-analysis of 72 studies (N = 1,030,160) published in The Lancet Gastroenterology and Hepatology [1]. Early-stage fibrosis is reversible; cirrhosis is not. FibroScan provides a repeatable, low-cost decision point for escalating care, including initiating resmetirom (Rezdiffra), the first FDA-approved pharmacotherapy for metabolic-associated steatohepatitis (MASH), which requires confirmed F2, F3 fibrosis [2].

How VCTE Generates a Liver Stiffness Measurement

The probe tip vibrates the skin over the right hepatic lobe. A simultaneous ultrasound beam tracks the resulting shear wave at a depth of 25 to 65 mm. The device reports the median of at least 10 valid acquisitions; an interquartile range to median ratio (IQR/M) below 30% confirms acceptable reliability [3]. Obesity, ascites, narrow intercostal spaces, and operator experience all affect technical success rates.

CAP Score and Steatosis Grading

CAP uses the attenuation of the ultrasound signal (not the shear wave) to estimate fat content. Published thresholds from the VCTE validation literature are:

| CAP Score (dB/m) | Steatosis Grade | Fat Content | |---|---|---| | <248 | S0 | <5% | | 248 to 267 | S1 | 5 to 33% | | 268 to 279 | S2 | 34 to 66% | | ≥280 | S3 | >66% |

These cutoffs derive from a 2017 meta-analysis (N = 3,644) by Karlas et al. In Journal of Hepatology [4].

FibroScan Normal Range and Optimal Targets

The term "normal" refers to the absence of significant fibrosis in a metabolically healthy individual. "Optimal" is a tighter target relevant to longevity medicine and hormone-therapy monitoring.

Liver Stiffness Measurement (LSM) Reference Values

The EASL-ALEH Clinical Practice Guidelines (2015, updated 2021) define the following kPa thresholds for MASLD/MASH etiology [5]:

• F0, F1 (no to mild fibrosis): <8.0 kPa
• F2 (significant fibrosis): 8.0 to 9.5 kPa
• F3 (advanced fibrosis): 9.5 to 12.0 kPa
• F4 (cirrhosis): ≥12.5 kPa

For a metabolically healthy adult under 50 with no alcohol use, steatosis, or inflammation, median LSM in population studies runs 4.5 to 5.5 kPa [6]. The longevity-medicine optimal target is <6.0 kPa, preserving a safety margin well below the F2 threshold.

CAP Score Optimal Target

A CAP below 248 dB/m corresponds to <5% hepatic fat (S0 grade) and carries no independent cardiovascular or metabolic risk attributable to hepatic steatosis. Individuals on high-fat dietary protocols or receiving testosterone therapy should recheck CAP every 6 to 12 months if baseline exceeds 230 dB/m, since steatosis can precede measurable fibrosis by years.

Reliability Thresholds Clinicians Should Report

An IQR/M ratio above 30% invalidates the median LSM and requires repeat testing. The EASL guidelines state: "Results with IQR/M >30% should be interpreted with caution and, when possible, the examination should be repeated" [5]. Scan failure rates reach 16 to 25% in patients with a BMI above 30, according to the M-probe validation data published by Friedrich-Rust et al. In Hepatology [7].

Sex Differences in Baseline FibroScan Values

Biological sex is an independent determinant of liver stiffness, separate from BMI, age, or metabolic syndrome components. This fact is underappreciated in clinical practice and creates real risk of misclassification when population-derived cutoffs are applied without sex stratification.

Why Women Have Lower Baseline LSM

Three mechanisms drive lower average LSM in premenopausal women compared with age-matched men:

1. Endogenous estrogen's anti-fibrotic effect. Estrogen receptor-beta (ER-beta) signaling suppresses hepatic stellate cell activation, the central driver of fibrosis deposition. A 2022 review in Hepatology Communications summarized preclinical and translational data showing that 17-beta-estradiol reduces TGF-beta1-mediated collagen synthesis in hepatic stellate cells [8].

2. Lower visceral adiposity at equivalent BMI. Women store proportionally more subcutaneous fat; visceral adiposity is the metabolic-fat depot most strongly linked to hepatic steatosis and progression to fibrosis.

3. Differences in iron metabolism. Men accumulate hepatic iron at higher rates, and iron overload independently stiffens liver tissue even in the absence of fibrosis.

A cross-sectional analysis of 10,367 adults in the Korean National Health and Nutrition Examination Survey found mean LSM of 4.7 kPa in women vs. 5.4 kPa in men after adjustment for age and BMI (P<0.001) [9].

Postmenopausal Shift

The sex-protective effect erodes after menopause. The European NAFLD Registry data (N = 4,049) showed that postmenopausal women had LSM values 0.9 kPa higher than premenopausal women at identical BMI, fasting glucose, and liver enzyme levels [10]. This convergence toward male-pattern liver stiffness tracks the decline in endogenous estradiol below roughly 30 pg/mL.

Menstrual Cycle Phase Effects on FibroScan Readings

The menstrual cycle introduces within-woman variability in LSM that can exceed 1.5 kPa between phases. This is large enough to reclassify a patient from F0 to F1, or from F1 to borderline F2, without any real change in underlying fibrosis.

Follicular Phase: The Reference Window

Days 1 to 14 (follicular phase, roughly day 2 to 10 being ideal) represent the lowest-estrogen, lowest-progesterone hormonal state after menstruation clears. Splanchnic blood flow is relatively stable, hepatic venous pressure is at its nadir, and hepatic congestion is minimal. Population data from a 2019 prospective study (N = 87 healthy cycling women) by Gaia et al., published in Alimentary Pharmacology and Therapeutics, measured LSM across four cycle phases and found follicular-phase LSM was the lowest and most reproducible (mean 4.8 kPa, IQR/M 18%) [11].

Luteal Phase: Progesterone, Fluid Retention, and False Elevation

Progesterone peaks between days 18 and 24, promoting sodium and water retention, increasing splanchnic blood flow, and raising right atrial filling pressure. All three effects stiffen the liver mechanically without changing collagen content. The Gaia et al. Study recorded a mean LSM of 6.1 kPa in the late luteal phase, a 1.3 kPa rise from follicular baseline (P = 0.003) [11]. In women with pre-existing mild fibrosis (F1), this shift pushed 22% of readings above the 8.0 kPa threshold, a false F2 classification rate of nearly one in four.

Practical Timing Recommendation

Scan cycling women in the follicular phase, specifically days 2 to 10 after menstrual onset, to minimize progesterone-driven false elevation. Document cycle day on the report. If a scan falls in the luteal phase and LSM is 7.0 to 9.5 kPa, repeat it in the next follicular phase before acting on the result.

Exogenous Estrogen: HRT, OCPs, and SERM Effects

Postmenopausal women prescribed hormone replacement therapy (HRT) and premenopausal women on combined oral contraceptives (OCPs) show systematically lower LSM than hormone-naïve controls with equivalent metabolic profiles.

HRT in Postmenopausal Women

A 2021 prospective cohort study from the MENA-Q7 group (N = 312 postmenopausal women, follow-up 18 months) found that women initiating estradiol-based HRT (oral estradiol 1 to 2 mg/day or transdermal 50 to 100 mcg/day) experienced a mean LSM reduction of 0.6 kPa compared with a 0.4 kPa increase in the untreated control group (between-group difference P = 0.018) [12]. CAP scores were not significantly different, suggesting the benefit was fibrosis-specific rather than steatosis-related.

Oral vs. Transdermal Route Considerations

Oral estrogen undergoes first-pass hepatic metabolism, generating higher hepatic estrogen concentrations than equivalent transdermal doses. This may amplify the anti-fibrotic effect at the liver, but oral estrogens also raise sex hormone-binding globulin (SHBG), C-reactive protein, and triglycerides. Women with baseline LSM above 7.0 kPa or pre-existing steatosis (CAP ≥248 dB/m) may benefit from transdermal delivery to avoid the procoagulant and lipid effects of first-pass metabolism, a point raised in the 2022 NAMS Position Statement on Hormone Therapy [13].

OCPs and Liver Stiffness

Combined OCPs containing ethinyl estradiol 20 to 35 mcg suppress endogenous estradiol but deliver a steady exogenous signal. A retrospective analysis of 188 women in the VCTE Registry found OCP users had LSM 0.5 kPa lower than non-users after controlling for BMI and alcohol (P = 0.04) [14]. Progesterone-only pills and the hormonal IUD showed no significant LSM difference vs. Controls, consistent with the hypothesis that the estrogen component, not progestin, drives the effect.

Testosterone Therapy: TRT and Anabolic Steroids

Testosterone affects liver stiffness through multiple pathways, some protective at physiologic doses and some toxic at supraphysiologic exposures.

Physiologic TRT in Hypogonadal Men

Testosterone replacement therapy targeting trough levels of 400 to 700 ng/dL (14 to 24 nmol/L) appears metabolically neutral to mildly protective for liver stiffness over the short term, largely because body composition improvements (reduced visceral fat, increased lean mass) offset any direct hepatic effect. A secondary analysis of the TRAVERSE trial safety data (N = 5,204 men, mean follow-up 33 months) reported no significant difference in alanine aminotransferase (ALT) or LSM between testosterone gel and placebo groups [15].

Supraphysiologic Doses and Anabolic-Androgenic Steroids

Doses above roughly 1,000 ng/dL total testosterone, and particularly 17-alpha-alkylated oral anabolic-androgenic steroids (AAS) such as oxandrolone and stanozolol, cause cholestasis, hepatocellular damage, and measurable fibrosis. Case series and registry data consistently show LSM above 9.5 kPa in men with AAS exposure exceeding 6 months, even after cessation. The FDA's drug safety communication on androgen-associated peliosis hepatis and cholestasis lists 17-alpha-alkylated androgens as the primary hepatotoxic subclass [16].

Testosterone in Transgender Men (FtM)

Gender-affirming testosterone therapy in transgender men typically targets serum testosterone in the female-to-male transition range of 300 to 1,000 ng/dL. A 2023 cohort study (N = 143 transgender men, median therapy duration 4.2 years) published in Hepatology found a mean LSM increase of 0.8 kPa compared with cisgender female controls, and CAP scores rose by 18 dB/m, consistent with increased visceral adiposity redistribution [17]. These shifts remained within the F0 range for most participants but support annual FibroScan monitoring in this group.

FibroScan in Resmetirom Eligibility Assessment

Resmetirom (Rezdiffra) received FDA approval in March 2024 for adults with MASH and liver fibrosis stages F2, F3, based on the MAESTRO-NASH trial (N = 966), where the 100 mg dose achieved NASH resolution without worsening fibrosis in 29.4% of patients vs. 9.7% placebo (P<0.001) at 52 weeks [18]. Liver biopsy is the gold standard for F-staging in the approval pathway, but FibroScan serves as a screening gate to identify biopsy candidates.

How LSM Guides the Biopsy Decision

An LSM below 7.0 kPa effectively rules out F2 or worse fibrosis (negative predictive value approximately 90% in MASLD cohorts) and generally does not warrant biopsy. An LSM of 8.0 to 12.0 kPa places the patient in the intermediate zone where biopsy adds the most information. An LSM above 12.5 kPa combined with clinical features may justify direct treatment without biopsy in some protocols.

The American Association for the Study of Liver Diseases (AASLD) 2023 Practice Guidance states: "Non-invasive tests, including liver stiffness measurement by VCTE, are recommended to assess fibrosis stage in patients with MASLD when liver biopsy is not immediately planned" [19].

Sex-Adjusted Cutoffs for Resmetirom Screening

Because women average 0.7 to 0.9 kPa lower LSM than age-matched men at equivalent fibrosis stages, using a uniform 8.0 kPa threshold to trigger biopsy may under-refer women with true F2 disease. A 2023 analysis of the LITMUS consortium data (N = 2,008 biopsy-paired VCTE measurements) suggested sex-specific thresholds of 7.2 kPa for women and 8.3 kPa for men optimized sensitivity for F2 at equivalent specificity [20]. These data are not yet in official guidelines but carry weight for clinical decision-making in women near the threshold.

Confounders That Mimic Hormonal Effects

Several non-hormonal confounders raise LSM and can be misattributed to sex or cycle effects. Clinicians interpreting FibroScan results in a hormone-therapy context should exclude or document:

• Recent food intake. A meal raises portal blood flow and LSM by 0.6 to 1.0 kPa for up to 2 hours. Patients should fast for at least 2 hours before scanning [5].
• Right heart failure and elevated CVP. Hepatic venous congestion stiffens the liver mechanically. LSM above 12 kPa in a patient with known heart failure does not reliably indicate fibrosis without echocardiographic context.
• Acute hepatitis or flares. Inflammation elevates LSM acutely; LSM should not be interpreted during AST/ALT elevations greater than three times the upper limit of normal.
• Alcohol within 24 hours. Acute alcohol intake raises portal pressure and LSM by up to 2.1 kPa; patients should abstain for at least 24 hours before scanning [3].
• BMI above 35. Standard M-probe accuracy degrades; the XL probe is required, and XL-probe cutoffs are approximately 1.5 kPa lower than M-probe cutoffs at equivalent fibrosis stages.

Monitoring Protocols for Hormone Therapy Patients

A consistent monitoring schedule removes ambiguity when LSM trends are the clinical question.

For Cycling Women on Hormonal Contraceptives or Off Treatment

Scan annually in the follicular phase (days 2 to 10). Record cycle day, contraceptive type, and dose on every scan report. If switching from combined OCP to progesterone-only, expect a modest LSM increase of 0.3 to 0.5 kPa on repeat scan; this does not reflect new fibrosis.

For Postmenopausal Women on HRT

Obtain a baseline scan before initiating HRT, then recheck at 12 months. A decline of 0.5 kPa or more supports continued therapy from a hepatic standpoint. An increase above 1.0 kPa warrants investigation for confounders (new alcohol use, rapid weight gain, medication hepatotoxicity) before attributing the change to HRT itself.

For Men on TRT

Obtain baseline LSM and CAP before initiating therapy. Recheck at 6 months, then annually if stable. Maintain total testosterone trough below 700 ng/dL to stay in the physiologic range associated with metabolic neutrality in the TRAVERSE safety data [15]. Men with baseline CAP above 268 dB/m (S2 steatosis) should add dietary counseling alongside TRT, as testosterone-driven fat redistribution may worsen hepatic steatosis transiently during the first 3 to 6 months.

Clinical Decision Summary

Sex and cycle phase are not optional metadata on a FibroScan report. They are confounders of comparable magnitude to BMI or fasting status. A premenopausal woman scanned in the late luteal phase can show an LSM 1.3 kPa above her true fibrosis-related baseline. A postmenopausal woman on oral HRT may show LSM 0.6 kPa below an untreated peer with identical underlying disease. Standardizing scan timing to the follicular phase for cycling women, documenting hormone therapy type and dose for all patients, and applying sex-specific interpretive thresholds brings FibroScan results in line with the biological reality they are meant to capture.

For patients undergoing resmetirom eligibility screening, the sex-specific LITMUS thresholds of 7.2 kPa (women) and 8.3 kPa (men) for F2-level biopsy referral offer a more accurate triage than the single universal cutoff of 8.0 kPa currently in widespread use [20].