How this calculator works
An effusion meets the biochemical exudate definition when any one criterion is positive: pleural/serum protein ratio above 0.5, pleural/serum LDH ratio above 0.6, or pleural LDH above two-thirds of the serum LDH upper reference limit. Equality does not meet a criterion. Diuretics and other circumstances can cause clinically transudative effusions to meet these biochemical criteria, so the result is not a cause or final diagnosis. The result is an estimate for information only and is not medical advice.
Formula
Exudate if fluid protein/serum protein >0.5 OR fluid LDH/serum LDH >0.6 OR fluid LDH > (2/3) x laboratory upper-normal serum LDH.
Worked example
Fluid protein 30 g/L and serum protein 60 g/L give exactly 0.5, which does not meet that criterion. Fluid LDH 120 U/L, serum LDH 200 U/L and upper limit 180 U/L give exact equality on both LDH thresholds too, so no criterion is met.
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Frequently asked questions
Is a value exactly at the threshold positive?
No. Each comparison is strictly greater than its threshold. Equality scores no positive criterion.
Why ask for the upper-normal LDH?
LDH reference limits vary by laboratory. The third criterion uses the serum upper limit, not the patient's serum LDH.
Does an exudate result identify cancer or infection?
No. It is a biochemical classification. The cause requires further clinical assessment and appropriate investigation.