CD4 and pneumonia: One reason for this incompatible observation we made is because there actually is no consensus on the diagnostic criteria for PCP.20 Although an elevated serum level of lactate dehydrogenase (LDH) or S-adenosylmethionine (SAM) has been suggested as surrogate markers for PCP, these clinical findings are not specific enough to distinguish PCP from other types of pneumonia.21,22 Another reason is that the patients with PCP had a very low CD4 level when admitted, so it was very likely that these patients had an additional bacterial infection.