Diagnostic performance of Xpert MTB/RIF in lymph node tuberculosis in a general hospital

Abstract

Background

In general hospitals, tuberculosis (TB) is an important infectious cause of lymphadenopathy, but its etiological diagnosis rate is very low. This study aimed to determine the performance of Xpert MTB/RIF(Xpert) in differentiate tuberculous lymphadenopathy from other causes.

Methods

A retrospective pairing study was carried out from August 2015 to July 2024. A total of 229 participants were involved. Microbiological reference standard (MRS) and composite reference standard (CRS) were used as two standards. All patients underwent biopsy measurement and specimens were examined using histopathology, acid-fast bacilli (AFB), liquid culture with/without Xpert. The baseline information, diagnostic methods and time were compared between two groups. The diagnostic values including sensitivity, specificity, accuracy (ACC), Kappa value and area under the curve (AUC) were compared.

Results

This study included a total of 229 participants, of whom 150 were in the no Xpert group and 79 in the Xpert group. The median age was 44 [31–58] years, with female proportion of 60.0%. The most common sites of lymphadenopathy are the neck (66%), mediastinum (17%), and abdomen (7%). In patients with lymph node tuberculosis (LNTB), MRS was achieved in 35.4% of cases, while 60.0% fulfilled CRS criteria. No significant differences were observed in MRS percentage or pathology positivity rates between the two groups. The median time from biopsy to diagnosis was significantly shorter in the Xpert group compared to the no Xpert group {2 days [interquartile range (IQR), 1–9 days] vs. 7 days (IQR, 5–15 days)}. In comparison to CRS, the sensitivity, specificity and AUC of Xpert were 57.1% [95% confidence interval (CI): 42.2–72.1%], 100%, and 0.786 (95% CI: 0.711–0.861), respectively. The sensitivity of the combined culture and Xpert significantly increased (71.4%, 95% CI: 57.8–85.1%). In comparison to MRS, Xpert shared same sensitivity with culture while specificity was paralleled. The combination of any two procedures yielded better results than single one, with the combined Xpert and pathology yielding 90.0% (95% CI: 83.4–96.6%), combined culture and pathology yielding 87.7% (95% CI: 80.5–94.8%), and combined culture and Xpert yielding 91.7% (95% CI: 80.6–100%).

Conclusions

Xpert can accelerate the microbiological diagnosis time and reduce the misdiagnose of lymph node granulomatous lesions. The application of Xpert combined with culture or pathology may be the best pattern for the diagnosis of LNTB in general hospital.

Highlight box.

Key findings

• The key findings of the study are that when Xpert MTB/RIF and pathology are combined, the sensitivity is 90.0% [95% confidence interval (CI): 83.4–96.6%] and the specificity is 73.3 (95% CI: 66.1–80.5%), whereas when culture and Xpert MTB/RIF are combined, the sensitivity is 91.7% (95% CI: 80.6–100%) and the specificity is 85.5% (95% CI: 76.1–94.8%).

What is known and what is new?

• Without conclusive microbiological evidence, treatment for lymph node tuberculosis (LNTB) is often initiated based on the histological demonstration of granuloma in excision biopsy.

• This article covered several illnesses that might result in lymph node granulomatous lesions. We assess the usefulness of Xpert MTB/RIF in the diagnosis of LNTB using a paired diagnostic test design.

What is the implication, and what should change now?

• The application of Xpert MTB/RIF combined with culture or pathology may be the best pattern for the diagnosis of LNTB in non-tuberculosis designated hospital.

Introduction

Numerous conditions, such as lymphomas, rheumatic illnesses, viral infections, metastatic cancer, and more, can result in lymphadenopathy (1,2). The most frequent infectious cause of adult lymphadenopathy is lymph node tuberculosis (LNTB). Also, it is the most common type of extrapulmonary tuberculosis (EPTB) (3). In 2023, an estimated global total of 10.8 million individuals fell ill with tuberculosis (TB) (4). In China, new TB cases in 2023 were 741,000, with an incidence rate of 52 per 100,000, accounting for 6.8% of global TB cases. The microbiological detection of Mycobacterium tuberculosis complex (MTBC) is paramount as it allows correct diagnosis and initiating effective treatment. Although the bacteriological confirmation rate of pulmonary tuberculosis (PTB) in China has increased, it is still lower than that in some low-income countries such as India (4). Even still, EPTB is not adequate (5).

The World Health Organization’s strategic endorsement of rapid molecular diagnostics has fundamentally transformed global TB diagnostic algorithms (6,7). In 2010, Xpert MTB/RIF (Cepheid, USA; henceforth referred to as Xpert) was developed to diagnose PTB with high sensitivity and specificity while concurrently identifying MTBC and rifampicin resistance (8). The recommendation to identify MTBC in non-pulmonary samples was then made. Although the body of research on using Xpert in lymph node samples is expanding (9-12), only a small number of studies have paired research and examined a variety of origins. Zhongshan Hospital is a tertiary-level university hospital in China with 3,000 beds that treats a wide range of multitudinous miscellaneous illnesses. We often face a mixture of various etiologies, and negative results from culture may not be sufficient to exclude TB. It is necessary to quickly differentiate between tuberculous lymphadenitis, malignant tumors (such as lymphoma), other granulomatous lesions [including non-tuberculosis mycobacteria (NTM) infection, or suppurative lymphadenitis]. An effective molecular diagnostic tool is imperative in differential diagnosis (13).

Existing researches are mostly based on TB specialized situations with high TB confirmation rate, while the patients in general hospitals are more complex as mentioned above. The specificity of Xpert under these mixed backgrounds lacks sufficient validation. We sought to determine the performance of Xpert MTB/RIF in MTBC detection for distinguishing LNTB from other causes of lymphadenopathy in this retrospective paired study. We hope that the findings of this study will elucidate the clinical utility of Xpert in managing complex cases, providing actionable insights for other general hospitals to optimize diagnostic and therapeutic strategies. We present this article in accordance with the STARD reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2071/rc).

Methods

Study design and population

This retrospective pairing study evaluated the data of patients with lymphadenopathy who presented at Zhongshan Hospital, Fudan University from August 2015 to July 2024. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The Ethical Review Committee of Zhongshan Hospital, Fudan University granted ethical approval for the study (approval No. B2024-310). Since this was a retrospective, non-interventional study, informed consent was not required. Among 278 patients with lymphadenopathy screened, 229 met the inclusion criteria and were enrolled in the study. All lymph node (LN) biopsy, pathological exam and etiological detection were all routine diagnostic process. We employed fresh tissue homogenates acquired via resection, endobronchial ultrasound-guided transbronchial needle biopsy (EBUS-TBNB), endoscopic ultrasonography-guided fine-needle biopsy (EUS-FNB), and percutaneous ultrasound-guided lymph node puncture.

This retrospective pre-post study was conducted based on the availability of Xpert testing in our hospital from March 2021 onward. Patients were divided into two groups according to whether they applied Xpert: no Xpert group and Xpert Group. For MTBC tests a positive culture or a positive polymerase chain reaction result of granuloma from paraffin section specimen, was referred to as the “microbiological reference standard” (MRS) (14). “Composite reference standard” (CRS) (15) referred to the following criteria combinations: 1+2+3 or 1+2+4 or 1+3+4 or 5. The following were the diagnostic criteria: (I) patient who presented with symptoms, signs, images indicative of LNTB; (II) positive tests for the release of interferon-gamma release assays (T-SPOT.TB assay); (III) histopathology finding of caseating granulomas with or without coagulation necrosis; or epithelioid cell aggregate with or without Langerhans giant cells and necrosis; (IV) a clinician has diagnosed TB and decided to undergo a full course of TB therapy; (V) bacterial confirmed cases of PTB or other parts of EPTB, accompanied by lymphadenopathy, excluded other diseases.

Xpert MTB/RIF assay

An equal volume of sample processing reagent was combined with the homogenate of lymph node tissue, vortexed for 15 seconds, and then left to stand at room temperature for 15 minutes. The GeneXpert Infinity System (Cepheid, California, USA) was then loaded with a sample of two milliliters of the processed liquid that was added to the Xpert reaction reagent cartridge. The findings were automatically read out by the system after two hours.

MTB liquid culture

The homogenate of lymph node tissue was to be digested, decontaminated, and concentrated using the Clinical and Laboratory Standards Institute (CLSI) standard methodology. After processing, 0.5 mL of the material is utilized to quickly cultivate mycobacteria (BACTEC™ MGIT™ 960, Becton, Dickinson and Company, New Jersey, USA). On a positive culture sample, MPB64 antigen detection and acid-fast staining confirmation were carried out.

Histopathological examination and acid-fast bacilli (AFB)

Tissue specimens were deparaffinized and rinsed with consecutive dilutions of alcohol. After being cut into 5-µm-thick slices, they underwent histological examination and were stained with either hematoxylin-eosin (HE) or Ziehl-Neelsen stain.

Statistical analysis

Our study is a diagnostic test study with a paired design. Using CRS as the gold standard, we compared the sensitivity of Xpert combined with culture versus culture alone. With predefined sensitivity values of 0.6 for Xpert combined with culture and 0.3 for culture alone, TB prevalence of approximately 30% in the included population, α=0.05, and 80% power, we employed a paired-sample sensitivity test. Sample size calculation using PASS software indicated that at least 70 patients undergoing both Xpert and culture tests were required.

Continuous variables were described as mean ± standard deviation (SD) and median and IQR according to data distribution. We applied Pearson’s Chi-squared test or Fisher test for categorical variables to compare the distributions among two groups. The Mann-Whitney U-test or t-test was used compared the characteristics between two group. The diagnostic effectiveness was assessed by computing the sensitivity, specificity, accuracy (ACC) and area under the curve (AUC) value for various methods. Kappa analysis was used to describe the level of data consistency. P<0.05 with two-tailed was considered to be statistically significant. Statistical analyses were performed using the R-3.6.1 software.

Results

Study population and baseline information

A total of 229 individuals were enrolled in the study: 150 patients in no Xpert group and 79 patients in Xpert group. The flowchart was shown in Figure 1. The baseline characteristics of the study population are shown in Table 1. There was no difference in gender, age, inflammatory markers, T-SPOT.TB results and proportion of TB patients in two groups. The median time from onset to diagnosis in no-Xpert group is shorter than that in Xpert group. Various lymph node biopsy sites and other etiology irrespective of LNTB are listed in Figure 2.

Figure 1.

Study design and flowchart of patient selection. CRS, composite reference standard; LN, lymph node; MRS, microbiological reference standard; TB, tuberculosis; Xpert, Xpert MTB/RIF.

Table 1. Baseline demographic and clinical characteristics of the study population.

Variables	Total (n=229)	No Xpert (n=150)	Xpert (n=79)	P value
Gender (female)	138 [60]	92 [61]	46 [58]	0.75
Age (years)	44 [31, 58]	40.5 [31, 56]	47 [30, 60.5]	0.28
WBC (×109/L)	6.06 [4.73, 8.06]	6.1 [4.77, 8.03]	5.94 [4.68, 8.09]	0.93
N (×106/L)	390.84 [268.75, 529.93]	389.17 [265.34, 523.44]	398.43 [282.3, 549.38]	0.72
CRP (mg/L)	13.65 [2.98, 42.83]	13.5 [2.35, 48.72]	13.95 [4.95, 38.17]	0.67
ESR (mm/H)	39 [20, 68.5]	39 [23, 69]	38.5 [20, 66.5]	0.57
Positive T-SPOT.TB	130 [57]	89 [59]	41 [53]	0.40
T-SPOT.TB ESAT-6	10 [0, 42]	11 [1, 46]	8.5 [0, 37]	0.22
T-SPOT.TB CFP-10	6 [0, 41.5]	8 [0, 49]	3.5 [0, 29.25]	0.14
Onset to diagnosis (d)	30 [21, 90]	30 [21, 90]	60 [30, 150]	0.01
Site				0.72
Neck	150 [66]	96 [64]	54 [68]
Mediastinum	40 [17]	28 [19]	12 [15]
Abdomen	17 [7]	13 [9]	4 [5]
Groin	13 [6]	7 [5]	6 [8]
Axillaris	9 [4]	6 [4]	3 [4]
CRS TB	119 [52]	77 [51]	42 [53]	0.90
MRS TB	81 [35]	57 [38]	24 [30]	0.32

Data are presented as n [%] or median [interquartile range]. CFP-10, Culture Filtrate Protein 10 kDa; CRP, C-reactive protein; CRS, composite reference standard; ESAT-6, Early Secreted Antigenic Target 6 kDa; ESR, erythrosedimentation; MRS, microbiological reference standard; N, neutrophil; WBC, white blood cell.

Figure 2.

Various lymph node biopsy sites and other aetiology irrespective of LNTB in different groups. LNTB, lymph node tuberculosis; TB, tuberculosis.

Different diagnostic variables in two groups

As demonstrated in Table 2, the positive rate of AFB was only 4% in this study, with an overall positive culture rate of 16% and positive pathology rate of 47%. Positive AFB, positive culture, positive pathology, positive pathology time, and pathology time did not differ between the two groups. In pathology, the positive rate of AFB was greater in the no Xpert group (18% vs. 6%), with a significant difference. The Xpert results were likewise displayed in Table 2, whereas no RIF-Resistance gene was discovered. In the no Xpert group, the medium time from biopsy to diagnosis was 7 (IQR, 5–15) days, longer than in the Xpert group [2 (IQR, 1–9) days] has a variation that is statistically significant.

Table 2. Different diagnostic variables in two groups.

Variables	Total (n=229)	No Xpert (n=150)	Xpert (n=79)	P value
Positive AFB	8 [4]	6 [4]	2 [3]	0.72
Positive culture	36 [16]	20 [14]	16 [20]	0.34
Culture time (d)	30.44±12.36	31.35±12.67	29.31±12.29	0.63
Positive pathology	106 [47]	73 [50]	33 [43]	0.41
AFB in pathology	32 [14]	27 [18]	5 [6]	0.03
Pathology time (d)	5 [4, 7]	5 [4, 7]	5 [4, 7]	0.96
Positive Xpert			24 [30]
Xpert degree
Negative			55 [70]
Very low			11 [14]
Low			8 [10]
Medium			5 [6]
Xpert RIF-R			0 [0]
Biopsy to diagnosis (d)	7 [3, 12]	7 [5, 15]	2 [1, 9]	<0.001

Data are presented as n [%] or mean ± standard deviation or median [interquartile range]. AFB, acid-fast bacilli; RIF-R, rifampin resistant.

Performance of different diagnostic methods in comparison to CRS and MRS standard

The sensitivity of Xpert was 57.1% [95% confidence interval (CI): 42.2–72.1%] in comparison to the CRS standard displayed in Table 3, which was higher than the sensitivity of the culture (32.1%, 95% CI: 23.5–40.8%), and the specificity was 100% overall. Pathology outperformed Xpert in terms of sensitivity at 77.4%, but its specificity was lower at 84.4% (95% CI: 77.6–91.2%). Compared to any single approach, the combined sensitivity of culture and pathology was 79.0% (95% CI: 71.7–86.3%), while its specificity was comparable to that of pathology. Comparing the combined culture and Xpert to either one alone approach, there was a significant increase in sensitivity (71.4%, 95% CI: 57.8–85.1%). The best ACC (0.701) and AUC value (0.857) are shown by combined culture and Xpert.

Table 3. Performance of different diagnostic methods in comparison to CRS and MRS standard.

Method	Sensitivity (95% CI)	Specificity (95% CI)	ACC (95% CI)	Kappa (95% CI)	AUC (95% CI)	P value
CRS as standard
Culture	0.321 (0.235–0.408)	1.000	0.316 (0.226–0.407)	0.653 (0.651–0.655)	0.661 (0.617–0.704)	<0.001a
Xpert	0.571 (0.422–0.721)	1.000	0.562 (0.402–0.723)	0.778 (0.651–0.655)	0.786 (0.711–0.861)	<0.001a
Pathology	0.774 (0.697–0.850)	0.844 (0.776–0.912)	0.617 (0.514–0.719)	0.808 (0.807–0.809)	0.809 (0.737–0.881)	<0.001a
Culutre + pathology	0.790 (0.717–0.863)	0.845 (0.778–0.913)	0.634 (0.534–0.734)	0.817 (0.815–0.818)	0.818 (0.747–0.888)	<0.001a
Culture + Xpert	0.714 (0.578–0.851)	1.000	0.701 (0.552–0.850)	0.848 (0.845–0.851)	0.857 (0.789–0.925)	<0.001a
Xpert + pathology	0.774 (0.697–0.850)	0.844 (0.776–0.912)	0.617 (0.514–0.719)	0.808 (0.807–0.809)	0.809 (0.737–0.881)	<0.001a
MRS as standard
Culture	0.667 (0.478–0.855)	0.860 (0.769–0.950)	0.526 (0.323–0.729)	0.802 (0.799–0.806)	0.763 (0.624–0.903)	<0.001b
Xpert	0.667 (0.478–0.855)	0.855 (0.761–0.948)	0.521 (0.316–0.726)	0.797 (0.793–0.801)	0.761 (0.620–0.901)	<0.001b
Pathology	0.848 (0.769–0.927)	0.731 (0.659–0.803)	0.537 (0.429–0.645)	0.772 (0.771–0.774)	0.790 (0.714–0.865)	<0.001b
Culture + pathology	0.877 (0.805–0.948)	0.730 (0.658–0.801)	0.559 (0.455–0.663)	0.782 (0.780–0.783)	0.803 (0.732–0.875)	<0.001b
Culture + Xpert	0.917 (0.806–1.000)	0.855 (0.761–0.948)	0.720 (0.561–0.880)	0.873 (0.871–0.876)	0.886 (0.784–0.987)	<0.001b
Xpert + pathology	0.900 (0.834–0.966)	0.733 (0.661–0.805)	0.582 (0.480–0.684)	0.792 (0.791–0.793)	0.816 (0.748–0.885)	<0.001b

^a, P<0.05 in AUC compared to CRS; ^b, P<0.05 in AUC compared to MRS. ACC, accuracy; AUC, area under the curve; CI, confidence interval; CRS, composite reference standard; MRS, microbiological reference standard.

The sensitivity of both Xpert and culture was 66.7% (95% CI: 47.8–85.5%) and the specificity was 86.0% (95% CI: 76.9–95.0%) vs. 85.5% (95% CI: 76.1–94.8%) respectively in comparison to the MRS standard displayed in Table 3. The results showed that the combination of any two procedures yielded better results than the single approach, with the combined Xpert and pathology yielding 90.0% (95% CI: 83.4–96.6%) and the culture and pathology yielding 87.7% (95% CI: 80.5–94.8%) vs. 91.7% (95% CI: 80.6–100%) in combined culture and Xpert. ACC (0.720) and AUC value (0.886) are highest for combined culture and Xpert.

Comparison of the distribution and overlap of positive results from the four tests

As seen in Figure 3, we discovered that ten specimens were judged to be positive only by pathology, whereas other diagnostic techniques produced negative results. Nevertheless, as illustrated in Figure 4, granulomatous lesion can still result from different illnesses. That accounted for the pathological examination’s low specificity. It was noteworthy that Xpert shared 11 positive results with culture and 19 positive results with pathology. Across the four tests, just one positive result was found.

Figure 3.

Visualization of TB detection test results: upset diagram of positive tests for Xpert group. The red column represents those Xpert were positive, and the yellow column represents those Xpert were negative. AFB, acid-fast bacilli; TB, tuberculosis.

Figure 4.

Clinical information of 17 patients with histopathology of granulomatous lesion besides tuberculosis. NTM, non-tuberculosis mycobacteria; TB, tuberculosis; Xpert, Xpert MTB/RIF.

Performance of Xpert in specimens obtained via different biopsy methods and anatomical sites

Table 4 illustrates that Xpert’s diagnostic performance in puncture samples was marginally worse than that in resection samples when compared to the CRS or MRS standard. When compared to the CRS standard, the sensitivity of Xpert in LN samples originating from the neck is higher than that in non-neck LN, at 70.0% (53.6–86.4%) vs. 25.0% (0.5–49.5%), respectively. In contrast to the MRS standard, the drawback of non-neck LN is less pronounced.

Table 4. Performance of Xpert in specimens obtained via different biopsy methods and anatomical sites in comparison to CRS and MRS standard.

Xpert	Sensitivity (95% CI)	Specificity (95% CI)	ACC (95% CI)	Kappa (95% CI)	AUC (95% CI)	P value
CRS as standard
Biopsy method
Puncture	0.500 (0.281–0.719)	1.000	0.750 (0.741–0.759)	0.750 (0.640–0.860)	0.500 (0.268–0.732)	<0.001a
Resection	0.636 (0.435–0.837)	1.000	0.805 (0.797–0.812)	0.818 (0.718–0.919)	0.619 (0.399–0.838)	<0.001a
Biopsy site
Neck LN	0.700 (0.536–0.864)	1.000	0.836 (0.831–0.841)	0.850 (0.768–0.932)	0.680 (0.498–0.861)	<0.001a
Non-neck LN	0.250 (0.005–0.495)	1.000	0.640 (0.622–0.658)	0.625 (0.502–0.748)	0.257 (0.003–0.517)	0.03a
MRS as standard
Biopsy method
Puncture	0.700 (0.416–0.984)	0.893 (0.778–1.000)	0.842 (0.835–0.849)	0.796 (0.597–0.996)	0.593 (0.301–0.885)	<0.001b
Resection	0.643 (0.392–0.894)	0.815 (0.668–0.961)	0.756 (0.747–0.765)	0.729 (0.530–0.928)	0.458 (0.171–0.744)	0.002b
Biopsy site
Neck LN	0.722 (0.515–0.929)	0.778 (0.642–0.914)	0.759 (0.753–0.766)	0.750 (0.579–0.921)	0.480 (0.239–0.721)	<0.001b
Non-neck LN	0.500 (0.100–0.900)	1.000	0.880 (0.872–0.888)	0.750 (0.550–0.950)	0.603 (0.217–0.990)	0.001b

^a, P<0.05 in AUC compared to CRS; ^b, P<0.05 in AUC compared to MRS. ACC, accuracy; AUC, area under the curve; CI, confidence interval; CRS, composite reference standard; LN, lymph node; MRS, microbiological reference standard.

Discussion

Lymphadenopathy is frequently seen in medical settings (1). Efficiently distinguishing between the numerous individuals with self-limited diseases and those with incurable diseases is of utmost importance. Among infectious diseases, LNTB is the most common in China (5,16) and seems to be both localized and widespread.

Discovering the organism MTBC in the biopsy samples or growing in culture is necessary for a conclusive diagnosis of LNTB. The MTB culture was disappointing, exhibiting low sensitivity and requiring a significant amount of time (4–8 weeks) (17), whereas liquid cultures, which are faster, demonstrated a positive result in an average of 2–4 weeks. Even the positivity rate for paucibacillary TB is modest. According to a national survey, seven times more clinically diagnosed patients—29.3%—had an EPTB diagnosis than those who had a laboratory confirmation (16). Without conclusive microbiological evidence, treatment for LNTB is often initiated based on the histological demonstration of granuloma in excision biopsy. The World Health Organization also suggests Xpert for non-pulmonary sample detection (such as lymph nodes, cerebral fluid, etc.) (6). In this study, we assessed the clinical usefulness in a general hospital in distinguishing TB from other complex cases.

Our findings indicated that the sensitivity of culture was 32.1% in comparison to CRS, which are consistent with those of other studies (18,19). The low sensitivity of culture is caused by the paucibacillary character of LNTB, loss of MTBC activity, and a number of intricate processes such grinding. Xpert’s average sensitivity in comparison to CRS and MRS was 57.1% and 66.7%. With pooled sensitivity and specificity of 79% (95% CI: 70–88%) and 94% (95% CI: 89–97%), respectively, Xpert MTB/RIF is particularly successful for the diagnosis of LNTB in children when compared to CRS, according to a meta-analysis (20). Our results might not be as sensitive because we used limited lymph node pus samples. Previous study indicated that pus had a higher sensitivity than tissue samples (11). Furthermore, the diagnostic efficacy of Xpert differs depending on the site of LNTB. The Xpert’s AUC of non-neck LN samples according to CRS was 0.257, whereas the AUC of neck LN samples was 0.680. This difference was not statistically significant, possibly due to the limited sample size. Compared to deep lymph nodes (such the mediastinum and abdominal cavity, which necessitate EBUS-FNB/EUS-FNB), cervical lymph node tissue is comparatively easy to collect, and coarse needle biopsy is practical. In comparison to CRS, Zhang et al. (21) recently revealed that Xpert had a greater sensitivity in a coarse needle biopsy sample of cervical LNTB (75.7% sensitivity and 98.7% specificity). The etiological diagnosis rate of the Xpert group is non-inferior to that of the no Xpert group, despite baseline data showing higher MTBC load and longer medium time from onset to diagnosis, which suggested that it may be easier to diagnose. Furthermore, Xpert showed a great advantage in biopsy to diagnosis time. The combination of Xpert and culture had good complementarity, with an increased sensitivity of 0.917 and specificity of 0.855 compared to MRS.

Pathology for TB was used to be a standard diagnostic technique for LNTB, which shows a greater sensitivity in diagnosing LNTB than other pathogenic diagnostic instruments. But there are still a lot of additional granulomatous disorders, both infectious and non-infectious (22). The typical pathological alterations are granulomatous inflammation with or without necrosis; however, NTM can still be difficult to differentiate even with a positive AFB staining (23). A negative Interferon-Gamma Release Assay (IGRA) excludes TB, except for in immunosuppressed or extremely ill individuals. Nonetheless, in regions such as China with a high incidence of LTBI (24,25), IGRA might test positive for granulomatous illnesses and be mistakenly identified as TB (26). Consequently, it has been discovered that IGRA is a helpful test for LTBI detection in granulomatous illnesses; nonetheless, a positive IGRA should not be used as a sole basis for TB diagnosis. Sarcoidosis and disseminated NTM infection share several similarities with TB, such as granulomatous inflammation and overlapping clinical presentations (fever, weight loss, fatigue, respiratory symptoms, and ocular involvement) (23,27), making the differential diagnosis difficult, particularly in nations with high TB incidence. In this study, two cases with a positive T-SPOT.TB were finally identified sarcoidosis and disseminated NTM infection, which highlighted the necessity of bacterial confirmation. Increased levels of blood angiotensin-converting enzyme (ACE) have been proposed as a diagnostic test for sarcoidosis (28); however, not all sarcoidosis patients have elevated ACE levels, and ACE is not specific because elevated levels are also seen in granulomatous infections (TB, leprosy, and syphilis). In situations where there is uncertainty regarding the pathological diagnosis, patients who have positive results from the Xpert can provide decisive evidence for reevaluating the clinical diagnosis of LNTB. Although specificity has not increased, the combination of Xpert and pathology can boost sensitivity and increase pathogenic evidence, both of which are highly beneficial.

Rapidly determining the drug-resistance status of MTBC is essential at the individual-patient level for appropriate treatment regimens. Genotypic drug susceptibility testing methods such as can be a rapid and cost-effective alternative to phenotypic drug susceptibility testing. There was no rpoB gene detected in our Xpert positive samples in this study. Genotypic drug susceptibility testing approaches such as can be a speedy and cost-effective alternative to phenotypic drug susceptibility testing. In the last three years, our institution has tested over 10,000 different samples, and the average positive rate for Xpert was 4.4% (0.36% for first treatment cases and 4.06% for retreatment cases). The lower limit of rpoB detection (29) and the relatively small Xpert positive sample number in this investigation could be caused by the negative. It is possible to further validate the phenotype drug sensitivity (30,31) or whole genome sequencing (WGS) of positive isolates (31), but neither was available in our local microbiology lab. Drugs’ reduced capacity to reach lymph nodes may be the main reason of the slow or poor progress observed in the anti-TB treatment of LNTB. Therefore, quick and accurate genotypic drug susceptibility data are essential for doctors to identify drug-resistant TB, which can significantly affect prognosis and anti-TB treatment.

There are some limitations in this study. Due to the retrospective nature of the study and its limited sample size, bias in patient selection was unavoidable. To further explore the diagnostic usefulness, a large-scale multicenter prospective, better paired or randomized study is necessary. Second, despite the low MTB bacterial load, no RIF-R findings were found, possibly as a result of the high RIF-R mutation lower limit and relatively low resistant in our population.

Conclusions

Xpert is rather helpful in differentiating between TB and other granulomatous diseases such as NTM, sarcoidosis, mycosis, bartonellosis, etc. when it comes to lymph node enlargement. When applied in combined with pathology or culture, Xpert can increase diagnostic sensitivity and ACC while reducing turnaround time. In high-TB burden locations, it might be the optimum pattern for the diagnosis of TBLN in non-TB designated hospitals.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethical Review Committee of Zhongshan Hospital, Fudan University in Shanghai, China (approval No. B2024-310). Since this was a retrospective, non-interventional study, informed consent was not required.

Data Sharing Statement

Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2071/dss

jtd-17-06-3619-dss.pdf ^{(142.6KB, pdf)}

DOI: 10.21037/jtd-2024-2071