β2 microglobulin and lactate dehydrogenase are indices of different features of Mycoplasma pneumoniae-associated community-acquired lower respiratory tract infection for severity evaluation in children.

Using the hospital records, we retrospectively assessed whether urinary β2 microglobulin/creatinine ratio (UBCR) and lactate dehydrogenase (LD) values could be used to estimate the severity of Mycoplasma pneumoniae-associated lower respiratory tract infection (MP-LRTI). We studied 48 patients with MP-LRTI (median age, 7.5 years; range, 3-14 years) admitted to Kagoshima City Hospital and examined the relationships of the UBCR or LD values with fever and pulmonary tissue damage (hypoxemia and severity assessments on chest radiographs). Patients were assigned to four groups based on whether they had fever and/or hypoxemia. Patients with high fever showed significantly higher UBCR values than those without (P < 0.05), whereas those with hypoxemia showed higher LD values than those without (P = 0.001). The maximum body temperature on admission was closely associated with the UBCR but not with LD levels. In chest radiography assessments, LD levels were significantly higher in patients with severe than mild or moderate MP-LRTI. A cut-off LD level of 530 IU/L showed a very high sensitivity (100%) and specificity (93%). Although UBCR values were higher in patients with severe MP-LRTI, the differences were not statistically significant. Our study shows that the UBCR is associated with body temperature, whereas LD levels may serve as an index of pulmonary tissue damage in children with MP-LRTI.