Utility of lactate dehydrogenase vs radiographic severity in the differential diagnosis of Pneumocystis carinii pneumonia.
OBJECTIVE
In patients with HIV infection, serum lactate dehydrogenase (LDH) level is commonly stated to be more elevated in Pneumocystis carinii pneumonia (PCP) than in non-PCP. We hypothesized that LDH level reflects radiographic extent and severity of pneumonia rather than P carinii infection specifically and therefore is not useful in the differential diagnosis of lung infections in AIDS.


METHODS
We compared radiographic features and LDH values in 93 sequential patients with HIV infection and a new hospital admission for pneumonia (53 PCP and 40 non-PCP) after excluding all patients with other potential causes for elevated LDH levels. The chest radiograph was graded using a quantitative scale (0 to 24) to assess radiographic extent and severity of pneumonia by two independent observers in blinded fashion. The relationship between radiographic score and hospital admission LDH level was analyzed by linear regression and Bayesian analysis was applied to different LDH ranges to calculate the clinical value of LDH measurements.


METHODS
Tertiary care teaching hospital and regional AIDS referral center.


RESULTS
Mean LDH level was higher in the PCP group (1.217 +/- 88 U/L compared with 776 +/- 55 U/L; p < 0.001), as was mean radiographic score (12.4 +/- 0.6 for PCP compared with 6.3 +/- 0.5 for non-PCP; p < 0.001). For the whole sample of 93, LDH level was significantly related to chest radiographic score (r = 0.43, p < 0.0001). Significant overlap occurred between the two groups at all levels of LDH such that no cutoff level could be established that impacted significantly on posttest probability of PCP, whereas a radiographic score of > 12 yielded a 96% posttest probability of PCP.


CONCLUSIONS
Serum LDH level reflects the degree of radiographic abnormality and is elevated in both PCP and non-PCP pneumonia to an extent that limits its utility in differentiating the two processes in hospitalized patients. The extent of radiographic involvement more clearly distinguishes the two conditions.
Boldt
M J
MJ
Department of Medicine, University of British Columbia, St. Paul's Hospital, Vancouver, Canada.
Bai
T R
TR
D017088:AIDS-Related Opportunistic Infections / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000201:enzymology; D000328:Adult; D001499:Bayes Theorem; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology; D003937:Diagnosis, Differential; D005260:Female; D005500:Follow-Up Studies; D015658:HIV Infections; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000097:blood*; D016013:Likelihood Functions; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D015588:Observer Variation; D010343:Patient Admission; D018410:Pneumonia, Bacterial / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000201:enzymology; D011020:Pneumonia, Pneumocystis / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000201:enzymology; D011336:Probability; D013902:Radiography, Thoracic; D016037:Single-Blind Method
D007770:L-Lactate Dehydrogenase