Light's criteria

Light's criteria to help decide whether a pleural effusion nature of exudate or transudate. Total protein concentration and lactate dehydrogenase activity in punctated effusion and blood serum are assessed.

The physiological upper limit of the LDH standard for adult men and women is up to 4,10 µkat/l.

These criteria tend to "overestimate" exudates. In controversial cases, they are therefore supplemented by so-called gradients:
 * Total proteinserum &minus; total proteineffusion > 31 g/l indicates transudate;
 * Albuminserum &minus; albumineffusion > 12 g/l indicates transudate.

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 * Pleural effusion