The clinical utility of serum lactate dehydrogenase in diagnosing pneumocystis carinii pneumonia among hospitalized AIDS patients.

It has been previously demonstrated that serum lactate dehydrogenase is elevated among HIV patients with pneumocystis carinii pneumonia (PCP). To evaluate the clinical utility of this test we analyzed the admission LDH levels of patients hospitalized for the first time due to the secondary complications of AIDS. Among 76 patients without a prior history of PCP, 41 (54%) had PCP diagnosed during their hospitalization while 35 (46%) did not have PCP. Serum LDH was significantly higher among PCP patients than in patients without PCP (mean = 423 IU/L vs 234 IU/L). Receiver operating characteristic curve analysis demonstrated that at an optimal cutoff point of LDH greater than or equal to 240 IU/L, the test sensitivity and specificity were 0.78 and 0.74 respectively among all hospitalized patients. However, when only patients with dyspnea were considered, the optimal test sensitivity and specificity improved to 0.94 and 0.78 at a cutoff point of LDH greater than or equal to 220 IU/L. Comparing the areas under fitted ROC curves, serum LDH was a significantly better discriminator among patients with dyspnea than among those who were not short of breath. We conclude that while serum LDH is strongly associated with the presence of PCP among AIDS patients, it is a poor screening test for PCP when applied to all hospitalized AIDS patients with and without respiratory complaints. Serum LDH is no substitute for appropriate microbiological studies. However, with further evaluation, it may prove to be a useful test in guiding the clinical management of dyspneic patients in whom sputum or bronchial examinations are negative or not immediately available.