SERUM LACTATE-DEHYDROGENASE (LDH) IN PNEUMOCYSTIS-CARINII PNEUMONIA, TUBERCULOSIS, AND BACTERIAL PNEUMONIA

An increase in serum lactate dehydrogenase (LDH) activity is commonly taken to support the presumptive diagnosis of Pneumocystis carinii pne umonia (PCP), although the LDH level may also be increased in other lu ng infections and in a variety of extrapulmonary disorders, To assess its diagnostic value in patients with fever, lung infiltrates, and a h igh prevalence of HIV infection, we compared LDH levels in 42 hospital ized patients with PCP, 71 with disseminated tuberculosis (TB), 40 wit h pulmonary TB, and 37 with bacterial pneumonia, Peak LDH level was hi gher (p<0.05) in patients with PCP (547+/-157 Un) and disseminated TB (569+/-338 U/L) than in patients with pulmonary TB (258+/-66 U/L) or b acterial pneumonia (331+/-139 U/L), However, substantial overlap betwe en groups limited its diagnostic value for individual patients, Expres sing LDH as its ratio to simultaneous serum aminotransferases (AST or ALT) did not enhance its discriminatory value, Most patients in each g roup had abnormalities in other serum enzymes (AST, ALT, alkaline phos phatase, gamma-glutamyltransferase), making an isolated elevation of L DH level uncommon (21% of PCP cases). Serum LDH has a high sensitivity for PCP (100% in this series) but must be interpreted with caution gi ven its lack of specificity.