Turnover of plasma proteins.

Abstract

Only turnover studies can reveal the mechanism behind an abnormal serum concentration of a given protein. Albumin, the major fraction of serum protein, is usually low when total serum protein is low and hence basic causes of hypoproteinaemia are much the same as those of hypoalbuminaemia: (1) increased catabolism which occurs in a variety of acute conditions such as acute infections, trauma including major surgery and myocardial infarction; (2) abnormal protein loss, which may be due to burns, severe proteinuria or gastrointestinal protein leakage; (3) decreased synthesis which is most often caused by liver disease or malnutrition and/or malabsorption; (4) haemodilution, which occurs in pregnancy, in some cases of cirrhosis of the liver and in surgical patients who have been overhydrated, especially when renal insufficiency is also present. The causes of hyperproteinaemia are fewer, because it is never due to decreased catabolism or abnormal retention. They include increased synthesis of immunoglobulins, either by normal clones (in chronic inflammatory conditions such as cirrhosis of the liver) or by abnormal clones (myelomatosis), which may produce a significant increase in total serum protein concentration; and haemoconcentration which is seen in severely dehydrated patients (cholera, pyloric stenosis) and increases haemoglobin as well as serum protein concentration. A normal total serum protein concentration does not necessarily imply normal concentration of individual fractions. It may, for instance, mask hypoalbuminaemia with hypergammaglobulinaemia,