Serum lactate dehydrogenase activity in patients with AIDS and Pneumocystis carinii pneumonia. An adjunct to diagnosis.

We investigated whether serum lactate dehydrogenase activity (LD) is significantly elevated in patients with acquired immunodeficiency syndrome (AIDS) and Pneumocystis carinii pneumonia (PCP) when compared to patients with non-Pneumocystis pneumonia. We measured LD (U/L), blood total lymphocyte count (1,000/cu mm), and alveolar-arterial oxygen tension difference P(A-a)O2 (mm Hg), in 30 patients with AIDS and PCP (group 1), four patients with AIDS or AIDS-related complex (ARC) and non-Pneumocystis pneumonia (NPCP) (group 2), and seven patients with pneumococcal pneumonia and bacteremia (PPB) (group 3). In patients with AIDS and PCP, LD was 509 +/- 35 (mean +/- SE), which was significantly elevated in comparison to both AIDS/ARC patients with NPCP (228 +/- 21) (p less than .001), and patients with PPB (211 +/- 21) (p less than .001). There was a significant positive correlation between LD and P(A-a)O2 (r = .51, p = 0.01). P(A-a)O2 was markedly elevated in both AIDS patients with PCP (48 +/- 3), and patients with pneumococcal pneumonia (44 +/- 3), but only moderately elevated in AIDS/ARC patients with NPCP (29 +/- 6). These results suggest that measurement of LD may be useful in differentiating Pneumocystis pneumonia from non-Pneumocystis pneumonia. In addition, the increase in LD correlates with the degree of pulmonary oxygen transfer abnormality.