Study objectives: To determine the predictive accuracy
of pH for identifying patients with malignant pleural effusions who
will fail pleurodesis.
Design: Analysis of published
and unpublished individual patient-level data retrieved from a MEDLINE
search and correspondence with primary investigators.
selection: Studies that reported pleural fluid pH values and
outcomes of pleurodesis for patients with malignant pleural
Data collection and analysis: Primary
investigators supplied data for 433 patients. Receiver operating
characteristic analysis and logistic regression estimated the
predictive accuracy, decision thresholds, and value of pleural fluid pH
compared with other clinical factors. The primary investigations were
graded for study design.
Results: Pleural fluid pH was
the only independent predictor of pleurodesis failure (odds ratio,
4.46; 95% confidence interval [CI], 2.69 to 7.45; p < 0.0001) and
had an area under the receiver operating characteristic curve (decision
threshold, ≤ 7.28) of 0.671 (95% CI, 0.624 to 0.715). The pH model
fit the data well (p = 0.48) with the probability of pleurodesis
failure increasing as pH decreased; specificity and negative predictive
values for pleurodesis failure exceeded 90% and 80%, respectively,
with a positive predictive value of 45.7% at pH values ≤ 7.15. The
primary studies had several important design limitations.
Conclusions: Using patient-level data, this study showed
that pleural fluid pH has only modest predictive value for predicting
symptomatic failure and should be used with caution, if at all, in
selecting patients for pleurodesis. The limitations of the primary
studies and low predictive accuracy should be considered when using
pleural fluid pH for patient care.