Neutrophil-to-Monocyte-Plus-Lymphocyte Ratio as a Potential Marker for Discriminating Pulmonary Tuberculosis From Nontuberculosis Infectious Lung Diseases

You La Jeon, MD, PhD; Woo-In Lee, MD, PhD; So Young Kang, MD, PhD; Myeong Hee Kim, MD, PhD

Disclosures

Lab Med. 2019;50(3):286-291. 

In This Article

Discussion

Because South Korea is a country with an intermediate-level TB burden, it is necessary to consider TB as an exclusive diagnosis for suspected infectious lung diseases.[12] It is important to discriminate TB at an early stage of disease evaluation because prompt isolation and treatment of TB can reduce its transmission. The findings of this study demonstrated that CBC data can provide a clinically important clue because primary laboratory results can provide an impression for discriminating TB from non-TB infectious lung diseases.

In this study, we analyzed the differences in CBC characteristics between patients with TB and non-TB infectious lung diseases, as well as the newly designed NMLR index based on CBC results. The NMLR showed strong power, compared with that of the original CBC parameters or other modified CBC indices, in distinguishing TB from non-TB infectious lung diseases.

The physiological immune response of peripheral leukocytes to general infectious diseases showed that patients had increased neutrophil counts and decreased lymphocyte counts, compared with those values in healthy subjects.[13–16] The NLR has been shown to be a predictive marker for various infectious diseases by maximizing these CBC characteristics. However, patients with TB are characterized by having an increased monocyte count, in addition to neutrophil increase and lymphocyte decrease.[5,6,8,9]

Two studies[8,17] have suggested the MLR as a predictive marker of TB, to differentiate patients with TB from healthy populations based on these findings. However, few reports suggest that the original CBC parameters or modified CBC indices may be helpful in the differential diagnosis of infectious lung diseases, including TB.

In the present study, we observed relatively increased neutrophil counts and decreased lymphocyte counts in the TB group, compared with those counts in the non-TB group. These results were consistent with those from a previous study comparing patients having TB with patients having bacterial pneumonia.[9] Also, there was no significant difference in the monocyte counts between the TB and non-TB groups; however, the monocyte percentage was significantly higher in the TB group (mean [SD], 8.91 [2.87] vs 6.19 [3.06]; P <.001; data not shown). The percentages of patients in the TB and non-TB groups with monocyte levels greater than 10% were 8.2% and 26.4% (P <.001), respectively. These results are associated with the role of monocytes in the pathophysiology of TB infection.

The host immune response to TB depends predominantly on monocytes/macrophages and lymphocytes, unlike in other infectious diseases.[18,19] TB is associated with increased production and release of monocytes in the bone marrow.[20] However, the role of neutrophils in the pathophysiology of TB remains unknown but is known to be limited.[21,22]

In the present study, the pathophysiologic characteristics of TB were reflected in the CBC data. The NMLR is a modified CBC index designed for this study, considering such differences in CBC parameters between patients in the TB and non-TB groups. The results of this study showed the NMLR to have a stronger discriminating power than those other previously reported indices, especially the NLR (AUC of NMLR and NLR, 0.90 and 0.88, respectively; P = .009). For cases of suspected pulmonary infectious disease, TB should be considered for NMLR values less than 3.95.

However, the value of AUC for differentiating patients with TB from healthy subjects was not high, although the NMLR of the patients with TB was significantly higher than that of the healthy subjects (Figure 2). Therefore, the NMLR is more suitable for discriminating TB among infectious lung diseases in patients than among healthy subjects.

The MLR and PLR were also analyzed in this study. They had lower AUC than those of the original CBC parameters, such as neutrophil or lymphocyte counts (AUC of MLR, PLR, neutrophil count, and lymphocyte count: 0.66, 0.62, 0.80, and 0.73, respectively). Therefore, MLR and PLR have low clinical usefulness for differentiating TB from non-TB infectious lung diseases.

CRP yielded a greater AUC than the original CBC parameters or MLR and PLR. However, CRP had a lower discriminating power (AUC, 0.83 [95% CI, 0.78–0.87]), compared with those of NLR or NMLR, for differentiating TB from non-TB infectious lung diseases, as confirmed in previous studies.[9,13]

In the present study, the NMLR showed better performance than the NLR for discriminating TB from non-TB infectious lung diseases, although the difference in their values was not itself great (Figure 1). The NMLR can be obtained by simple calculation of CBC parameters, so it can be easily applied in clinical practice.

The limitations of this study include the irregular age distributions between patients in the TB and non-TB groups and the fact that the study was conducted retrospectively and in a single center. Because the patients with non-TB mycobacterial infection were excluded in this study, the findings of the study cannot be applied in this population.

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