Pleural effusion: parapneumonic: biochemical tests helped predict the need for drainage.

Clinical bottom line (level 2a)

  1. Parapneumonic effusions often became purulent or require drainage.
  2. Patients with a low pleural fluid glucose or pH or high LDH were likely to have a complicated course.
  3. Patients with a high pH were unlikely to have a complicated course.
Heffner et al: American Journal of Respiratory Critical Care Medicine 1995; 151: 1700-1708
Expires April 2003

The study

Systematic review of all of
  • Patients: pleural effusion
  • Intervention: pleural fluid pH, glucose and LDH
  • Outcome: differential diagnosis of complicated from uncomplicated parapneumonic pleural effusions


    • Articles found in all using MEDLINE, 1966 to 1995 (search terms: detailed in text ) and bibliographies were also searched.

    Selection criteria: as above
    Appraisal criteria: selected by two independent reviewers using set criteria (detailed in text)
    Articles excluded if: pneumonia could not be separated from other causes of pleural effusions

    seven studies involving 274 hospitalised patients were included
    • target disorder: complicated parapneumonic effusion
    • independent unblinded reference standard applied in all patients from an appropriate spectrum
    • diagnostic test: pH, glucose, LDH
    There was no comment on whether the studies were significantly heterogeneous.

    The evidence


    diagnostic test complicated effusion uncomplicated effusion LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)
    glucose <2.0 mmol/l 32 3 16
    (5.2 to 50)     		91%
    ( to )
    glucose 2.0 to 5.0 mmol/l 11 18 0.92
    (0.47 to 1.8)     		38%
    ( to )
    glucose <5.0 mmol/l 11 60 0.28
    (0.16 to 0.47)     		15%
    ( to )
    LDH >1600 (U/ml) 22 5 8.1
    (3.3 to 20)     		81%
    ( to )
    LDH 600 to 1600 U/ml 10 18 1.0
    (0.53 to 2.0)     		36%
    ( to )
    LDH <600 U/ml 8 51 0.29
    (0.15 to 0.55)     		14%
    ( to )
    pH <7.2 80 12 9.9
    (5.7 to 17)     		87%
    ( to )
    pH 7.2 to 7.3 14 17 1.2
    (0.63 to 2.4)     		45%
    ( to )
    pH >7.3 7 121 0.086
    (0.042 to 0.18)     		5%
    ( to )
    total . .

    • pre-test probability of complicated effusion: 40% (95% CI: 32% to 48%)

    Comments

    1. Data would be clinically more useful if presented as multilevel likelihood ratios.
    2. Data was reconstructed from dot plots. Cut-offs were based on ROC curves.
    3. All the studies had small numbers of patients and used different definitions of a complicated effusion. There was not enough data to see whether a combination of the three tests was better than each alone.

    Citation

    1. Heffner JE, Brown LK, Barbieri C, et al: Pleural fluid chemical analysis in parapneumonic effusions: a meta-analysis. American Journal of Respiratory Critical Care Medicine 1995; 151: 1700-1708
    Search Terms: pleural effusion in Cochrane
    Contributor: Chris Ball and Clare Wotton, April 2000
    Reviewer: Mitsuhiro Kamei

    Clinical Question.
    Patient pleural effusion
    Intervention or Exposure pleural fluid pH, glucose and LDH
    Outcome diagnosis of complications