Factors which can confound pleural fluid interpretation
| Biomarker | Confounder | Results |
|---|---|---|
| PF protein | Diuretic therapy | Concentrated pleural effusion causing a higher level of PF protein or LDH and, therefore, leading to a misclassification as an exudate |
| PF pH12 | Air, time delay in processing | Falsely elevates pH, all air should be expelled from the syringe and processing should occur within 4 hours |
| Local anaesthetic | Falsely lowers the pH | |
| Loculations | Different locules of a pleural effusion can have different pH measurements | |
| PF microbiology | Contaminants | Skin commensals are occasionally cultured in PF. Positive PF cultures should be interpreted with caution if the biochemical PF results and clinical picture are not in keeping with infection |
LDH = lactate dehydrogenase; PF = pleural fluid.