Practical Utility of Lactate Dehydrogenase in the Diagnosis of Human Immunodeficiency Virus-Related Pneumocystis carinii Pneumonia

To the Editor.—  I have read with interest the concise article by Glatt and Chirgwin¹ regarding Pneumocystis carinii pneumonia (PCP) in human immunodeficiency virus-infected patients, and I want to add what may be, in my opinion, important practical information on the topic of nonspecific tests as an aid to diagnosis.It has been shown that serum lactate dehydrogenase (LDH) activity level is increased in patients with acquired immunodeficiency syndrome-related PCP^2-4 and can be used as an indirect tool for diagnosis. Unfortunately, perhaps because of the statistical method used in most studies comparing mean values from different groups of patients but not drawing conclusions on a case-by-case basis, the use of the LDH activity level as an indicator of PCP remains largely undervalued.^1,5I and my colleagues⁵ have shown that when an HIV-infected patient presented with a first episode of subacute interstitial pneumonia, as defined by the