Determination of serum total protein by the Kjeldahl method

Chromý et al. found in 2009, that albumin-calibrated analysis of serum total protein according to a candidate reference method, developed by Doumas working group in 1981, provide results with unacceptable positive bias. The simplest way to rectify this defect is the use of serum and/or plasma-based protein standards certified by the Kjeldahl method. We reviewed Kjeldahl methods adopted by laboratory medicine and selected for total protein a direct analysis on washed protein precipitates with trichloroacetic acid and verified its preliminary analytical performance parameters. We describe a final simplified analysis with modified still unit and digestion flask serving for both digestion and distillation and present its re-validation.