Pleural effusion: Light's criteria helped rule out exudative effusions.

Clinical bottom line (level 4)

  1. In patients with pleural effusions, if none of the Light's criteria for an exudate were met, this made an exudative effusion much less likely (LR-0.036) .
Romero et al: Chest 1993; 104 (2): 399-404
Expires April 2003

The study

Setting: university hospital, Spain

297 patients (aged range 8 to 95 years; mean 57, 54% male) with pleural effusions referred for diagnostic thoracentesis

Excluded if
  • indeterminate cause of effusion
  • effusion due to multiple superimposed diseases



    • Independent unblinded reference standard, applied in some patients from a consecutive appropriate spectrum.
    Reference standard:
    • final clinical diagnosis of a disorder consistent with an exudate:
      • malignancy: malignant cells on cytology or in biopsy specimen, or histologically-proven malignancy with exclusion of other causes
      • parapneumonic: acute febrile illness with purulent sputum and pulmonary infiltrate
      • tuberculosis pleurisy: positive culture for Mycobacterium tuberculosis or pleural biopsy showing typical epithelioid cell granuloma
      • pulmonary infarction: strong clinical suspicion and high-probability perfusion scan or abnormal angiogram
    Diagnostic test: Light's criteria for an exudate: any of:
    • protein effusion: serum ratio > 0.5
    • LDH > 307 IU/ml
    • LDH effusion: serum ratio > 0.6

    • validation of a clinical prediction guide

    The evidence

    pre-test probability of exudate: 85%, (95% CI: 81% to 89%)

    differential diagnosis number of patients prevalence
    (95% CI)
    transudates: congestive heart failure 31 10%
    (7% to 14%)
    liver cirrhosis 8 2.7%
    (0.9% to 4.5%)
    nephrotic syndrome 5 1.7%
    (0.2% to 3.1%)
    exudates: malignant effusions 132 44%
    (39% to 50%)
    parapneumonic effusions 49 17%
    (12% to 21%)
    tuberculosis 43 15%
    (11% to 19%)
    pulmonary embolism 18 6.1%
    (3.3% to 8.8%)
    other cause 11 3.7%
    (1.6% to 5.9%)


    diagnostic test exudate transudate LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    protein ratio 222 4 9.7
    (3.8 to 25)     		98% 0.13
    (0.092 to 0.19)     		43%
    LDH 165 0 inf
    (9.9 to inf)     		100% 0.35
    (0.29 to 0.41)     		66%
    LDH ratio 231 8 5.0
    (2.7 to 9.5)     		97% 0.10
    (0.066 to 0.16)     		37%
    Light criteria 245 10 4.3
    (2.5 to 7.4)     		96% 0.036
    (0.017 to 0.076)     		17%
    total 252 44

    Comments

    1. The reference standard was not clearly stated in the text.
    2. There may be spectrum bias since fewer patients with transudates would have been referred for thoracentesis.

    Citation

    1. Romero S, Candela A, Martin C, et al: Evaluation of different criteria for the separation of pleural transudates from exudates. Chest 1993; 104 (2): 399-404
    Search Terms: reference from Pleural effusion chapter in 'Quick Consult Manual to Evidence-based Medicine' by Lee, Hsu and Stasior: publd. Lippincott-Raven, 1997
    Contributor: Chris Ball and Clare Wotton, October 2000
    Reviewer:

    Clinical Question.
    Patient pleural effusion
    Intervention or Exposure Light's criteria
    Outcome exudate