The meaning of a high monocyte to lymphocyte ratio in tuberculosis

<b>Introduction:</b> Several studies have reported an association between a high monocyte to lymphocyte ratio (ML ratio) and tuberculosis (TB). We did not find the ML ratio to be a useful marker of TB disease, due to low sensitivity and negative predictive value for development of disease (BTS Winter Meeting 2018). The reported association may be due to selection bias towards sputum smear-positive pulmonary TB (S+PTB). We examine whether the ML ratio holds any clinical value. <b>Methods:</b> A normal range for ML ratio was calculated using anonymised general practitioner full blood counts from 2974 adults, excluding abnormal parameters such as raised neutrophil count. ML ratios were compared for different forms of TB. Clinical features of S+PTB cases with cut-off ML ratio 0.45 were compared using Chi-squared, Students’ t-test or Mann-Whitney U-tests. <b>Results:</b> The control group mean ML ratio was 0.27, cut-off 0.45 (mean +2SD). S+PTB patients had the highest ML ratios (med 0.63; IQR 0.40-0.80) compared to all other forms of TB disease (med 0.33; IQR 0.22-0.50, p&lt;0.001). S+PTB patients with ML ratio &gt;0.45 had more severe disease and greater radiographic involvement, lower albumin levels and albumin:globulin ratio, but were not significantly different. Although sputum conversion was equally good in both groups, treatment duration was often increased on clinical grounds. <b>Conclusions:</b> The ML ratio is an indicator of S+PTB, but does not reflect disease severity or prognosis.