Agreement and reliability of transient elastography in patients with chronic hepatitis C - a cross-sectional test-retest study

doi:10.21203/rs.3.rs-2232604/v1

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Agreement and reliability of transient elastography in patients with chronic hepatitis C - a cross-sectional test-retest study

https://doi.org/10.21203/rs.3.rs-2232604/v1

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Background

Transient elastography (TE) has largely replaced liver biopsy to evaluate fibrosis stage and cirrhosis in chronic hepatitis C. Previous studies report excellent reliability of TE but agreement metrics have not been reported. This study aimed to assess inter-rater agreement and reliability of repeated TE measurements.

Methods

Two operators performed TE independently, directly after each other. The primary outcome was disagreement, defined as a difference in TE results between operators of ≥ 33%, as well as the smallest detectable change, SDC₉₅ (i.e., the difference between measurements needed to state with 95% certainty that there is a difference in underlying stiffness). Secondary outcomes included reliability, measured as intra-class correlation, and patient and examination characteristics associated with agreement.

Results

In total, 65 patients were included, with a mean liver stiffness of 9.7 kPa. Of these, 21 (32%) had a disagreement in TE results of ≥ 33% between the two operators. The SDC₉₅ on the log scale was 1.97, indicating that an almost twofold increase or decrease in liver stiffness would be required to confidently represent a change in the underlying fibrosis. Reliability, estimated using the intra-class correlation, was acceptable at 0.86. In a post-hoc analysis, fasting less than 5 hours before TE was associated with a higher degree of disagreement (48% vs 19%, p = 0.03).

Conclusions

In our clinical setting, agreement in directly repeated TE measurements was surprisingly low. It is essential to further investigate the reliability and agreement of TE to determine its validity and usefulness.

transient elastography

hepatitis C

agreement

reliability

inter-observer

Early identification of fibrosis and cirrhosis of the liver enables prevention and treatment of long-term consequences of chronic hepatitis C, including liver failure, hepatocellular cancer, and death.¹ Even where antiviral treatment is generally offered, fibrosis and cirrhosis staging affect decisions regarding surveillance, for hepatocellular cancer and oesophageal varices.² Traditionally, liver biopsy has been the reference standard of fibrosis and cirrhosis assessment, despite being associated with discomfort and complications.³ Transient elastography (TE) is a non-invasive method for measuring liver stiffness that has replaced LB in a majority of patients with chronic hepatitis C.⁴ Due to its non-invasive nature, TE is also suitable for longitudinal monitoring.

Previous studies suggest comparable accuracy between liver biopsy and TE to detect fibrosis in hepatitis C patients.^{5, 6} Studies have reported excellent test-retest reliability for TE.^7–11 Reliability refers to an instrument´s ability to discriminate between study subjects and may be excellent even with considerable measurement error if the population is heterogenous.^12–15 Agreement, in contrast, refers to differences of measurements on the original scale (kPa for TE). Whether agreement is acceptable is a situation-dependant clinical consideration and can be related to the smallest detectable change (SDC).^{13, 16} SDC corresponds to the following clinical question: if a patient has performed TE previously, how much higher, or lower, must a new TE result be to confidently represent a change in underlying fibrosis? This question cannot be addressed using reliability statistics alone and, to the best of our knowledge, agreement metrics or SDC have not been addressed in previous studies.

The aim of the present study was to assess agreement, SDC, and reliability of repeated measurements of liver stiffness of TE in chronic hepatitis C patients, and to explore factors associated with disagreement.

Study setting and patients

This was a cross-sectional observational study, conducted at the outpatient clinic of the infectious diseases department of Helsingborg Hospital, in the south of Sweden, serving a population of approximately 250 000 inhabitants. Patients were recruited by convenience sampling between November 2018 to February 2022. Eligibility criteria was non-pregnant adult (≥ 18 years) patients with chronic hepatitis C, as defined by at least one positive serum-HCV-RNA and no evidence of acute hepatitis C. Data on age, sex, date, operators, probe used (medium or XL), stiffness (kPa), time since last intake of food (hrs), time since last intake of alcohol (days), length (cm), weight (kg), HCV genotype, and liver biomarkers were recorded.

Transient elastography procedures

Liver stiffness was measured in kPa using the Fibroscan^® device (Echosens, Paris, France), for which the reported kPa value was the median of 10 consecutive measurements. The interquartile range divided by the median (IQR-%) was noted. The TE was considered valid when 10 consecutive successful measurements had been gathered, and the IQR-% was lower than 30%, as in clinical routine. The Fibroscan^® was operated by a total of 9 individuals: 8 medical doctors and 1 specially trained nurse. The majority (n = 6) of the medical doctors were specialists in infectious diseases, and two were resident physicians. All operators had been certified by the company behind Fibroscan^®, but none of the operators were experienced operators, as all had performed less than 500 exams. Patients were put in the recommended body position, with the right arm on top of the head and legs positioned towards the left. This body position was unaltered during the entire procedure. Patients were assessed twice by each operator, with the probe removed between examinations. The second operator assessed the patients directly after the first. Operator one and two performed the measurements independently, and operator two were unaware of the results from the previously performed TE. The probe position for the previous measurement was not known but typical marks generated by the probe on the patient remained. Operators could select a medium or XL-probe at their own discretion based on the patient’s configuration.

Categorisation of liver stiffness scores

Continuous scores in kPa were categorised into stages (F-scores) using cut-off values suggested by Castera et al.: F0/F1 ≤ 7.1 kPa, F2 > 7.1 and < 9.5, F3 ≥ 9.5 and < 12.5 and F4 (cirrhosis) ≥ 12.5.¹⁷ We further prespecified a dichotomous cut-off where a difference in liver stiffness between operator one and two of ≥ 33% was considered unacceptably high. In a worst-case scenario, this could correspond to a two step-change in F-score staging (e.g., 9.4 kPa (F2) ⋅ 1.33 = 12.5 kPa (F4)).

Outcomes

The primary outcome was disagreement, expressed as 1) the proportion of participants with inter-rater differences at or above our prespecified threshold (33%) and 2) the smallest detectable change, representing the difference needed to state with 95% certainty that a change had occurred in the underlying fibrosis (SDC₉₅). Reliability was the secondary outcome, for continuous stiffness measurements as well as for fibrosis stage categories.¹⁸ As an exploratory outcome, patient and exam characteristics associated with inter-rater differences above our prespecified threshold of ≥ 33% in liver stiffness were evaluated.

Statistics

Agreement

The first rating for each operator was used for inter-rater analysis. We estimated the 95% limits of agreement (LOA₉₅, the range encompassing 95% of differences), as described by Bland and Altman.¹⁶ We expected heteroscedasticity (i.e., larger differences at the higher end of the scale) and measurements were transformed using the natural logarithm. The standard error of measurement (SEM) was estimated on the log scale and SDC₉₅ was derived from SEM.¹³

Reliability

A one-way random effects intra-class correlation (ICC_1,1) was used to estimate reliability in continuous kPa.^{13, 16} Cohen´s Kappa was evaluated for the F score as well as separately for the dichotomous outcome of F0-3 vs F4 (cirrhosis no vs yes). ICC and Kappa values are expressed with 95% confidence intervals within brackets. Intra-rater agreement and reliability was determined using the same methods.

Factors associated with discordance in liver stiffness

The other baseline variables were explored for associations with the dichotomous disagreement outcome, using non-parametric tests throughout.

Participant and liver stiffness characteristics

In total, 66 patients were asked to participate, of which one declined, and 65 were included. In 60 patients, four (2+2) valid measurements were obtained by the two operators, and in five patients, three (2+1) measurements were obtained (in one patient one measurement was invalid, and in four patients the second rating was not performed). There were 255 examinations performed overall. For inter-rater analysis, 130 measurements were used (65 ´ 2) and for intra-rater analysis, 250 measurements (125 ´ 2) were used. The patient and examination characteristics are displayed in Table 1 and Table 2, respectively.

Agreement

The results of the first and second operators are displayed in Figure 1. In total, 23 patients (35%) were classified into different F-scores by the first and second operators, of whom 8 (12% of all) had an F4 discrepancy, see figure 2. Inter-rater disagreement at or above the prespecified threshold of 33% were found in 21 out of 65 patients (32%). The LOA₉₅ on the original scale was 0.6 ± 7.7 kPa and Bland-Altman plots confirmed heteroscedasticity and the need for log transformation, see fig 3A and 3B as well as supplementary tables S1 and S2. Furthermore, one extreme outlier affected the results and was addressed in a sensitivity analysis, see supplementary table S3. This analysis did not change results significantly and the outlier was kept in the analysis.

The SEM was estimated at 0.24 on the log scale, corresponding to a SDC₉₅ of 0.68. After back-transforming the logged values, the SDC₉₅ was estimated to 1.97. This implies that for a patient with a previous TE result of 8.0 kPa, a new result would have to be either below 4.1 kPa (8.0 / 1.97) or above 15.8 kPa (8.0 ´ 1.97) to represent a change in the underlying fibrosis with 95% certainty.

Reliability

Inter-rater reliability, estimated by intra-class correlation (ICC), was 0.86 (0.78 - 0.91). When liver stiffness was categorised into F-scores, the weighted Kappa (with equal weights) was 0.66 (0.53 - 0.79). The corresponding Kappa value for the dichotomous comparison of F4 vs F0-3 was 0.64 (0.41 - 0.87).

Intra-rater analysis

In intra-rater analysis, all metrics were better. The F-scores were discordant in 24 of 125 (19%) and only 10 of 125 (8%) examinations had a disagreement above the prespecified threshold of ≥ 33%. The SDC₉₅ was 1.40. For intra-rater reliability, the ICC was 0.96 (0.94 - 0.97). After categorization, the equal-weighted Kappa was 0.84 (95 CI: 0.77 - 0.90) and the dichotomous Kappa (F4 vs F0-3) was 0.95 (0.88 - 1.0).

Factors associated with inter-rater disagreement

When associations with disagreement ≥ 33% were explored, none of the 9 individual operators were under- or over-represented (all operators with ≥ 5 examinations were involved in discordant ratings in between 29% and 40%). The only factor associated with a disagreement ≥ 33% was shorter duration of fasting before elastography, see Table 3. Due to this association, we performed a post-hoc analysis, where inter-rater differences were plotted versus fasting time (see supplementary figure S5). Graphically, there seemed to be better agreement when the participant had fasted ≥ 5 hours. We performed a subgroup analysis for long fasting (≥ 5 hours) versus short fasting, where each group consisted of 31 of 62 participants with data on fasting time. Inter-rater disagreement of ≥ 33% were notably more common in the short fasting group (48% vs 19%, p = 0.03, c² test).

In this cross-sectional study of hepatitis C patients monitored by TE, we describe inter-rater agreement, which has not been previously reported. In our setting, 32% of patients had an inter-rater disagreement above our prespecified threshold. Furthermore, an almost twofold increase or decrease in kPa was required to represent a change in the underlying fibrosis with 95% certainty. In a post-hoc analysis, we found that longer fasting time before TE was associated with better inter-rater agreement.

The two TE operators found different F-scores in 35% of participants, compared to previous studies ranging from 23–35%.^{7, 8, 11, 19} Although agreement metrics or SDC have not been presented before, a few studies provide Bland-Altman plots, from which LOA₉₅ could be roughly estimated. A study by Fraquelli et al. showed LOA₉₅ of bias ± approximately 4 kPa.⁹ Another study by Perazzo et al. found systematic bias between operators but also seem to display a LOA₉₅ of bias ± approximately 10 kPa.⁷ Our LOA₉₅ on the original scale was bias ± 7.7 kPa, although heteroscedasticity (also suggested in previous studies) complicates the comparison. Thus, agreement in the current study seems to be on the lower end compared to previous studies.

Inter-rater reliability, measured by ICC, was 0.86 which could be considered “good to excellent” but is also on the lower end compared to previous TE studies ranging from 0.76 to 0.98.^{7–11, 20} The Kappa value of 0.64 for F4 vs F0-3 was lower compared to 0.75 and 0.80 in previous studies, but categorised values could be more sensitive if they are close to cut-offs.^{7, 8} Reliability measures may also be lower in a more homogenous study population. Our population had a lower median LS than in previous studies, with 15% having a unanimous F4 rating, compared to 18–36% in previous studies, possibly indicating a more homogenous population, with lower kPa values.^{7–9, 11, 19} Reclassification is less likely in the higher range as all values above 12.5 kPa would be F4. To conclude, both larger variations as well as a more homogenous population could have affected reliability negatively.

In a post-hoc analysis, agreement was better when patients had fasted for ≥ 5 hours. Previous studies on fasting time have shown that 150 minutes after a meal, liver stiffness has returned to baseline.²¹ However, we found that the variability seemed to be increased up to 5 hours after food intake, although in a secondary analysis. Previously, high BMI, liver biomarkers, and high IQR-% have also been associated with invalid TE measurements.²² We did not find an association with these factors and TE inter-rater variability. Findings related to operator experience have been conflicting.^{8, 22–24} Our results did not suggest systematic differences between operators, although statistical power was insufficient for formal analysis. In two participants, the two operators used different probes (medium and XL), resulting in large kPa differences, as seen in Table 3.

Reliability and agreement metrics were much better in intra-rater than inter-rater analysis, indicating that the change of operator introduced variability. In the intra-rater situation, the operator had more information, i.e., was not blinded to probe placement, probe angle, choice of probe, or the results from the previous exam. Even though the reliability metrics were excellent, the intra-rater SDC₉₅ was 1.40, signalling a higher variability than the IQR-% for the 10 readings of each result. This may be explained by the fact that, in the intra-rater situation, the probe was removed and then replaced, in contrast to the 10 repeated measurements of each LS result. The protocol did not specify that the same probe location should be used, and previous studies suggest variability due to probe location.²⁵

This study has several limitations. We used many operators, who did not have extensive experience in an international context. However, all operators were certified and are performing TE within clinical routine. The sample size was relatively small, making it sensitive to outliers, as elaborated in the supplementary appendix. In the inter-rater analysis, there was information bias, as marks from the preceding procedure could be visible, which could decrease variability if the same probe location was chosen. On the other hand, the operator was blinded to the previous choice of probe (which would normally be documented) and in two cases using different probes resulted in high variability.

This is a small study, and our results need verification in other settings. As TE is increasingly being used in other diagnoses, studies in these should be emphasised as well, including in hepatitis B, In such studies, reporting both reliability and agreement should be encouraged, employing the GRRAS (Guidelines for reporting reliability and agreement studies) guidelines.²⁶ From a clinical perspective, our finding that eight patients (12%) received different F4 ratings is important as this would entail different allocation to screening for hepatocellular cancer. This suggests that values close to cut-offs with clinical importance should be scrutinised, that repeated TE and / or liver biopsy considered in selected patients. Furthermore, the wide range of SDC₉₅ suggest that it may be difficult to determine whether changing TE results in longitudinal monitoring represent measurement error or progressive fibrosis. Lastly, our post-hoc analysis emphasise the importance of fasting before TE and that clinicians may consider postponing TE in the case of insufficient fasting.

In our clinical setting, agreement in repeated TE measurements was surprisingly low. It is essential to further investigate the reliability and agreement of TE in patients with chronic liver diseases to determine its validity and usefulness.

Ethical approval and consent to participate

The Regional Ethical Review Board in Lund, Sweden approved the study (2018-688). All patients included in the study signed informed consent. All methods were carried out in accordance with the declaration of Helsinki and the GRRAS (Guidelines for reporting reliability and agreement studies) guidelines.²⁶

Availability of data and materials

The underlying dataset cannot be publicly shared, due to ethical concerns. The underlying data may be requested by individual researchers from the corresponding author upon reasonable request if an approval is granted by the Swedish Ethical Review Authority. Such requests will also be evaluated by the Data Protection Officer at Skåne University Hospital.

Consent to publish

Not applicable.

Acknowledgements

The authors are most grateful for nurse Christina Sperlingsson, dr Jonas Bläckberg, dr Johan Sundler, dr Anna Stjärne Aspelund and dr Anna-Clara Ivarsson gathering data as TE operators.

Funding

OL- funding of research from the Tegger and Stig and Ragna Gorthon foundations. GT - the governmental funding of research within the clinical health services (ALF).

Conflict of interests:

None.

Author Contributions:

The study was conceived by OL, JT, JO and CK, who also perfomed data acquisition. The study design was finalised by OL and GT. Data analysis was performed by GT. The manuscript was drafted by OL and GT and critically revised by JT, JO and CK. All authors approved submission of the final version of the manuscript.

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Table 1. Patient characteristics of included patients.

Patient characteristics
age	46 (35-57)
Male sex	51 (78%)
Time since food intake, hrs (n = 62)	5 (2-12)
Time since alchol intake, days (n = 63)	30 (4-182)
Body mass index, kg/m2, (n=62)	25 (22-29)
HCV Genotype
1a	24 (37%)
1b	4 (6%)
2b	7 (11%)
2c	1 (2%)
3a	29 (45%)
HCV-RNA, million copies (n = 64)	2 (0-5)
ALT, ucat/L (n = 64)	1.4 (0.8-2.2)
AST, ucat/L (n = 58)	0.9 (0.6-2.1)
Albumin, g/L (n = 54)	41 (38-43)
Platelets, count (n = 59)	246 (197-291)
Bilirubin, umol/L (n = 50)	8 (6-11)
ALP, ucat/L (n = 57)	1.4 (1.1-1.7)
GT, ucat/L (n = 54)	1 (0.6-2.2)
PK-INR (n = 59)	1 (1-1.1)

Table 1. Continuous variables are expressed as median (IQR), categorical as n (%), n = 65 unless otherwise specified. HCV = hepatitis C virus, ALT = alanine transaminase, AST = aspartate aminotransferase, ALP = alkaline phosphatase, GT = gamma-glutamyl transferase. PK – INR = prothrombin complex concentrate.

Table 2. Characteristics of included exams.

Examination characteristics
Medium probe	225 (87%)
X-large probe	32 (12%)
Stiffness, kPa	7.3 (5.4-10.5)
IQR-%, n = 254	13 (9-18)
F-score
F0/F1	118 (45%)
F2	63 (24%)
F3	21 (8%)
F4	53 (20%)

Table 2. Continuous variables are expressed as median (IQR), categorical as n (%). N = 255 unless otherwise specified. ^*F-scores according to Castera ¹⁷.

Table 3 Patient and examination characteristics by inter-rater differences.

	difference < 33%, n = 44	difference ≥ 33%, n = 21	p value
age	47 (37-57)	42 (35-58)	0.88
Male sex	33 (75%)	18 (86%)	0.51
Time since food, hrs	7 (4-14)	3 (2-5)	0.01
Time since alcohol, days	15 (2-168)	60 (21-365)	0.14
BMI	25 (22-29)	26 (21-30)	0.89
HCV-RNA, million copies	2.2 (0.5-4.9)	1.6 (0.3-5.4)	0.71
ALT, ucat/L (n = 64)	1.4 (0.8-2.8)	1.2 (0.7-1.8)	0.44
AST, ucat/L (n = 58)	1 (0.6-2.1)	0.9 (0.6-1.2)	0.39
Albumin, g/L (n = 54)	41 (38-43)	40 (39-42)	0.92
ALP, ucat/L (n = 57)	1.4 (1.2-1.7)	1.4 (1.1-1.8)	0.89
GT, ucat/L (n = 54)	1.1 (0.7-2.2)	0.6 (0.4-1.7)	0.20
PK-INR (n = 59)	1 (1-1.1)	1 (1-1.1)	0.43
probe change	0 (0%)	2 (10%)	0.19
IQR-%, highest	16 (11-21)	17 (15-20)	0.61
HCV Genotype			0.66
1a	15 (34%)	9 (43%)
1b	2 (5%)	2 (10%)
2b	6 (14%)	1 (5%)
2c	1 (2%)	0 (0%)
3a	20 (45%)	9 (43%)

Table 3. Inter-rater differences have been dichotomised into below or above the prespecified threshold (33%). Continuous variables expressed as median (IQR), categorical as n (%). HCV = hepatitis C virus, ALT = alanine transaminase, AST = aspartate aminotransferase, ALP = alkaline phosphatase, GT = gamma-glutamyl transferase. PK – INR = prothrombin complex concentrate.

No competing interests reported.

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Agreement and reliability of transient elastography in patients with chronic hepatitis C - a cross-sectional test-retest study

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Abstract

Background

Methods

Results

Conclusions

Figures

Introduction

Methods

Study setting and patients

Transient elastography procedures

Categorisation of liver stiffness scores

Outcomes

Statistics

Results

Discussion

Conclusion

Declarations

References

Tables

Additional Declarations

Supplementary Files

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