Effects of Light’s criteria on the diagnostic accuracy of pleural fluid carcinoembryonic antigen concentrations for malignant pleural effusion

Abstract

The pleural fluid carcinoembryonic antigen (CEA) test is a diagnostic tool for malignant pleural effusion (MPE). Light’s criteria are an important method for the differential diagnosis of pleural effusion. This study aimed to analyze the effects of Light’s criteria on the diagnostic accuracy of CEA concentrations. The subjects of this study were from a retrospective cohort (BUFF study) and a prospective cohort (SIMPLE study). All participants had pleural effusion with undetermined cause. We extracted data on the basic clinical characteristics, final diagnoses, and pleural fluid CEA concentrations of the patients from their medical records. Spearman correlation analysis was used to explore the correlations between CEA concentrations and serum, lactate dehydrogenase (LDH), and total protein levels in the pleural fluid. Logistic regression analysis was used to investigate the relationship between Light’s criteria and false-negative CEA results. A total of 340 patients with pleural effusion of unknown etiology were included in this study, including 118 patients with MPE patients and 222 patients with benign pleural effusion (BPE). In all patients, as well as in those with BPE or MPE, the pleural fluid CEA concentration was positively correlated with the total protein ratio, the LDH ratio, and pleural fluid LDH activity, with correlation coefficients of approximately 0.3. In patients with negative CEA results, an LDH ratio greater than 0.6 was independently associated with false-negative CEA results. In patients with negative pleural fluid CEA results, an LDH ratio greater than 0.6 suggests a false-negative result.

Introduction

Pleural effusion is a common clinical sign with common causes, including congestive heart failure, tuberculous pleuritis, malignant tumors, and pneumonia^1,2. Correctly identifying the etiology is a prerequisite for the scientific management of patients with pleural effusion. Differentiating between transudate and exudate is the first and most critical step in determining the cause of pleural effusion. Currently, the criteria proposed by Light in 1972 are the most commonly used method for differentiating exudate from transudate³. According to these criteria, if any one of the following three conditions is met, exudative effusion is considered; otherwise, transudative effusion is considered: (i) the activity of lactate dehydrogenase (LDH) in the pleural fluid is greater than two-thirds of the upper limit of the serum reference range; (ii) the ratio of pleural fluid to serum LDH is greater than 0.6; or (iii) the ratio of pleural fluid to serum protein is greater than 0.5³. The sensitivity of Light’s criteria for diagnosing exudative effusion is close to 100%, but the specificity is only approximately 70%⁴. Therefore, serum and pleural fluid LDH and total protein tests are the most common biochemical tests for pleural fluid.

Although Light’s criteria are highly accurate for differentiating exudative from transudative effusion, they cannot identify the specific etiology. Malignant pleural effusion (MPE) is one of the most common causes of exudative effusion^2,5. MPE occurs in up to 15% of all cancer patients⁶. Common cancers that cause MPE include lung cancer, breast cancer, mesothelioma, and gastrointestinal tumors^7,8. The presence of MPE indicates advanced metastatic cancer and a poor prognosis, with a median survival of 3 to 12 months^9,10. The gold standards for diagnosing MPE are cytological examination, pleural biopsy, and thoracoscopy^9,11, but these diagnostic methods have certain limitations¹². Although cytological examination has the advantages of low cost and high specificity, its sensitivity is less than 60%¹³, and the diagnostic accuracy depends on the type of primary tumor and the experience of the cytologist¹⁴. Although the diagnostic accuracy of thoracoscopy can reach over 90%¹⁵, thoracoscopy is an invasive examination that can cause some surgery-related complications, such as pain, bleeding, and infection^16,17. In addition, thoracoscopy requires special training, limiting its application by clinicians in remote areas.

In comparison, pleural fluid tumor markers are effective tools for diagnosing MPE because of their simplicity, short turnaround time, objectivity, and minimally invasive nature^{18, 19–20}. Systematic reviews and meta-analyses have shown that the sensitivity and specificity of CEA concentrations in diagnosing MPE are 60% and 97%, respectively^21,22. In other words, if we use CEA concentration alone to diagnose MPE, the false-negative rate is 40%. Although CEA cannot be used to define or exclude MPE when used alone, it can help pulmonologists estimate the risk of MPE, and thus potentially improve the diagnostic efficiency of patients with undiagnosed pleural effusion. Identifying factors that can cause false-negative CEA results can improve the clinical interpretation of CEA concentrations, thereby facilitating MPE’s diagnostic accuracy. Therefore, this study aimed to explore the relationship between Light’s criteria and false-negative CEA test results. We reported this work in accordance with the Standards for Reporting Diagnostic Accuracy Studies (STARD) guidelines²³.

Methods

Participants

The included participants were from the SIMPLE study and the BUFF study. The SIMPLE study was a prospective and double-blind diagnostic accuracy study²⁴. We recruited patients with pleural effusion of undetermined cause who visited the Emergency Department and the Department of Respiratory Medicine of the Affiliated Hospital of Inner Mongolia Medical University (from September 2018 to July 2021) and the Affiliated Changshu Hospital of Nantong University (from June 2020 to July 2021). The BUFF study was a retrospective study that included patients who visited the Affiliated Hospital of Inner Mongolia Medical University from July 2017 to July 2018 due to pleural effusion of undetermined cause²⁵. The inclusion criteria were as follows: (i) patients with pleural effusion of undiagnosed etiology and (ii) patients who underwent diagnostic thoracentesis. Pleural effusion was confirmed by chest X-ray, CT, or ultrasound. The exclusion criteria were as follows: (ⅰ) patients with pleural effusion within the last three months but whose etiology was clear; (ii) patients who developed pleural effusion during treatment or hospitalization; (iii) patients aged < 18 years; (iv) pregnant patients; (v) patients with pleural effusion caused by trauma or surgery; and(vi) patients with missing data on pleural fluid CEA, LDH, total protein, and serum LDH and total protein concentration. This study was approved by the Ethics Committees of the Affiliated Hospital of Inner Mongolia Medical University (NOs. 2018011, 2021014) and the Ethics Committee of Changshu Hospital Affiliated with Nantong University (KY2020-KY-009). In the SIMPLE study, all participants signed informed consent forms. In the BUFF, this study is retrospective in nature, and the requirement for informed consent was waived by the Ethics Committees of the Affiliated Hospital of Inner Mongolia Medical University. We performed this study in accordance with the Declaration of Helsinki.

Diagnostic criteria

The diagnostic criteria for pleural effusion were described in our previous studies^24,26. Briefly, MPE is diagnosed by pleural fluid cytology or pleural biopsy. In participants with negative cytology who were unable or unwilling to undergo pleural biopsy, the presence of late-stage cancer and the exclusion of other benign pleural diseases led to the diagnosis of MPE. Tuberculous pleural effusion (TPE) was diagnosed by Ziehl-Neelsen staining, culture, nucleic acid amplification test, pleural biopsy, or the response to antituberculosis treatments²³. Parapneumonic pleural effusion (PPE) was diagnosed on the basis of clinical features, a positive pleural fluid microbiological culture, imaging findings (encapsulation), pleural biopsy, the response to antibiotic therapy, and laboratory test results²⁴. Heart failure (HF) was diagnosed on the basis of clinical signs, biochemical indicators (serum NT-proBNP level, Light’s criteria), cardiac function tests, and the response to diuretic treatment. Two senior physicians (Zhi-De Hu and Li Yan) made the final diagnoses of the participants by reviewing their medical records. Disagreements were resolved through consultation.

Measurement of pleural fluid CEA concentrations

We extracted the clinical data of the patients at admission from their electronic medical records, including demographic characteristics and some pleural fluid and serum biochemical indicators. The levels of pleural fluid CEA in both cohorts were measured via an Architect I2000SR immunoassay analyzer (Abbott Laboratories, USA). The laboratory technicians who determined the CEA level were not aware of the patients’ final diagnoses.

Statistical analysis

Continuous variables are presented as the median and interquartile range (IQR). Categorical variables are expressed as absolute numbers and percentages. We used the Shapiro-Wilk test to assess the normality of continuous data. Spearman correlation analysis was used to examine the relationships between pleural fluid CEA concentrations and serum and pleural fluid LDH and total protein concentrations. Based on previous studies^21,27, we set the threshold of the pleural fluid CEA concentration at 10 ng/mL. In MPE patients, a CEA concentration ≥ 10 ng/mL was considered a true-positive result, whereas a CEA concentration < 10 ng/mL was considered a false- negative result. Univariate and multivariate logistic regression analyses were used to investigate the associations between Light’s criteria and false-negative and false-positive CEA results. The conditional backward method was used for variable selection. When the relationship between Light’s criteria and false-positive CEA results was analyzed, the study subjects tested positive for CEA (CEA > 10 ng/mL). When examining the relationship between Light’s criteria and false-negative CEA results, the study subjects tested negative for CEA. All the statistical analyses were performed using R (version 4.0.4). A two-sided p value < 0.05 was considered to indicate statistical significance.

.

Results

Basic characteristics of the participants

Figure. 1 shows the flowchart of participant selection in this study. A total of 340 patients with pleural effusion of undetermined cause were included (118 with MPEs and 222 with BPEs). Among these patients, 86 had a CEA concentration ≥ 10 ng/mL, whereas 254 had a CEA concentration < 10 ng/mL. The basic clinical characteristics of the participants are shown in Table 1.

Table 1. Characteristics of the participants.

Characteristics	All (n = 340)	BPE(n = 222)	MPE(n = 118)	p
Age, years	71 (63–79)	71 (61–79)	71 (63–79)	0.77
Gender, male (%)	227 (67)	156 (70)	71 (60)	0.08
Pleural fluid
WBC, 106/ml	965 (478–2010)	935 (397–2138)	998 (625–1760)	0.59
Glucose, mmol/L	5.8 (4.5–6.8)	5.7 (4.5–6.8)	5.9 (4.6–6.7)	0.72
LDH, U/L	243 (132–509)	207 (109–498)	313 (186–579)	0.003
ADA, U/L	11 (6–24)	14 (6–35)	9 (6–13)	0.002
Protein, g/L	32 (20–43)	29 (17–42)	37 (26–43)	< 0.001
CEA, ng/mL	2 (1–10)	1 (1–2)	42 (4–424)	< 0.001
Serum
Protein, g/L	62 (57–69)	61 (56–69)	64 (60–68)	0.07
LDH, U/L	209 (176 − 259)	207 (175 − 258)	214 (179 − 262)	0.38

Data are presented as the median (25th–75th centile) or absolute number (percentage). Abbreviations: BPE, benign pleural effusion; MPE, malignant pleural effusion; WBC, white blood cell; LDH, lactate dehydrogenase; ADA, adenosine deaminase; CEA, carcinoembryonic antigen.

Fig. 1 [Images not available. See PDF.]

Flowchart of participant selection. CEA, carcinoembryonic antigen.

Influence of Light’s criteria on false-negative CEA results

Figure. 2 shows the correlations between the pleural fluid CEA concentration and the protein ratio, pleural fluid LDH concentration, and LDH ratio in patients with pleural effusion. We observed that in all patients, as well as in those with BPE or MPE, the pleural fluid CEA concentration was significantly positively correlated with the total protein ratio, LDH ratio, and pleural fluid LDH concentration. The correlation coefficients ranged from 0.22 to 0.35 (all p < 0.05). These results suggested that the diagnostic accuracy of the CEA concentration may be related Light’s criteria.

We performed univariate and multivariate logistic regression analyses to investigate the relationships between Light’s criteria and false-positive CEA results in patients who tested positive for CEA but found no associations (data not shown). However, in patients who tested negative for CEA, the LDH ratio was associated with false-negative CEA results (Table 2). Patients with an LDH ratio greater than 0.6 were more likely to have false-negative results.

Table 2. Univariate and multivariate analysis of Light criteria associated with false-negative carcinoembryonic antigen.

	N	True negative	False negative	Univariate analysis		Multivariate analysis
				OR (95%CI)	p	OR (95%CI)	p
Protein ratio ≥ 0.5	117	94	23	1.73 (0.88–3.46)	0.117	-	-
Protein ratio < 0.5	137	120	17
LDH ratio ≥ 0.6	174	141	33	2.44 (1.09–6.25)	0.043	2.44 (1.09–6.25)	0.043
LDH ratio < 0.6	80	73	7
LDH ≥ 160, U/L	151	124	27	1.51 (0.75–3.17)	0.261	-	-
LDH < 160, U/L	103	90	13

OR, odds ratio.

Fig. 2 [Images not available. See PDF.]

Correlation analysis between pleural fluid carcinoembryonic antigen and lactate dehydrogenase and protein in serum and pleural effusion. PF: pleural effusion; LDH, lactate dehydrogenase; CEA: carcinoembryonic antigen. *: p < 0.05; **: p < 0.01.

Discussion

The use of pleural fluid biomarkers plays an important role in the differential diagnosis of pleural effusion. However, the diagnostic accuracy of these biomarkers is influenced by various factors. For example, our previous study revealed that the accuracy of the pleural fluid adenosine deaminase concentration in diagnosing tuberculous pleuritis is affected by age²⁸. Therefore, analyzing the relationships between biomarkers is highly important for the differential diagnosis of pleural effusion. Adjusting for these confounding factors can help clinicians better interpret the diagnostic value of biomarkers. For example, since age is associated with D-dimer levels, the use of age-adjusted D-dimer cutoff values can more accurately screen for pulmonary embolism²⁹.

Pleural fluid CEA is the most widely investigated tumor marker for MPE. It cannot confirm or rule out MPE when used alone, and it only has limited value in verifying the histological type and molecular phenotype (e.g., EGFR mutations, ALK translocations, PD-1/PDL-1) of the primary tumor; however, increased CEA is highly suggestive of MPE. Therefore, tumor marker determination can help pulmonologists estimate the probability of MPE and determine the necessity of further invasive diagnostic procedures³⁰. In this study, we analyzed the relationships among pleural fluid CEA and LDH concentrations, the LDH ratio, and the total protein ratio. We found that the pleural fluid CEA concentration was correlated with all three items of Light’s criteria, suggesting that the diagnostic accuracy of the CEA concentration may be influenced by these three factors. The results of the logistic regression analysis indicated that the LDH ratio was associated with false-negative CEA results. Among patients with an LDH ratio greater than 0.6, the proportion of patients with false-negative CEA results was approximately 20% (33/174). However, among patients with an LDH ratio less than 0.6, the proportion of patients with false-negative CEA results was only approximately 8.8% (7/80). Therefore, when the pleural fluid CEA concentration is used to diagnose MPE, the LDH ratio should be taken into account. Among patients with unexplained pleural effusion and negative CEA test results, those with an LDH ratio greater than 0.6 have a greater likelihood of a false-negative CEA result.

Although this is the first study to explore the impact of Light’s criteria on false-negative CEA results, it has several limitations. First, our sample size was relatively small, which prevented us from exploring how to reduce the occurrence of false-negative CEA results by adjusting the LDH ratio. Second, since there were only 8 cases of false-positive CEA results in patients with BPE, we were unable to verify the impact of Light’s criteria on false-positive CEA results in these patients. Third, 19% of MPE patients in our cohort was not defined by cytology and histology. Alternatively, they were diagnosed by two senior physicians by reviewing the clinical data, treatment responses, follow-up information, and the exclusion of common benign pleural effusions. Although we have tried our best to make a diagnosis, the risk of misdiagnosis cannot be completely excluded. It is a dilemma to handle these patients because excluding these patients from the final analysis may impair the representativeness of the cohort, and thus negatively affect the reliability of our findings.

In conclusion, our study revealed a significant positive correlation among pleural fluid LDH, total protein, and CEA concentrations, and that Light’s criteria can affect the determination of CEA concentrations in patients with MPE. It is necessary to conduct large sample studies in the future to verify this conclusion.

Author contributions

ZD.H. and TW.J. designed and supervised the study. DN.Y. and YN.X. collected, analyzed the data and drafted the manuscript. Y.N., JX.W., L.Y., W.J. analyzed the data. L.Y. and ZD.H. made the diagnoses. ZD.H., TW.J., and WQ.Z critically reviewed and edited the manuscript. All authors have accepted responsibility.

Funding

This work was supported by Inner Mongolia Medical University Zhiyuan Talent Project (ZY20243120), the Program of Inner Mongolia Medical University (YKD2023MS042), and Suzhou Multicenter Clinical Research Program for Major Diseases (DZXYJ202416).

Data availability

The datasets generated and/or analysed during the current study are not publicly available due to ethical restrictions, but are available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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