nonalbumin

Nonalbumin is a term used in laboratory medicine to describe the portion of a protein sample that is not albumin. It is commonly discussed in relation to urine or serum protein analyses, where separating albumin from nonalbumin proteins helps interpret the underlying physiology of protein excretion or systemic protein status.

In urine, normal excretion contains small amounts of albumin and other proteins. Albumin is often the focus of proteinuria screening because it is a major component of kidney-related loss. Nonalbumin proteins in urine include low molecular weight proteins such as Tamm-Horsfall protein (uromodulin), enzymes, and small immunoglobulin fragments. In tubular proteinuria, nonalbumin proteins tend to be relatively increased, reflecting proximal or distal tubular dysfunction with impaired reabsorption of filtered proteins (for example, beta-2 microglobulin or retinol-binding protein). In overflow proteinuria, excess production of specific proteins, such as immunoglobulin light chains in multiple myeloma, can contribute to the nonalbumin fraction as well as to albumin, depending on their size and filtration.

In laboratory reporting, nonalbumin can be derived as total protein minus albumin, or identified as a separate fraction by electrophoretic methods (e.g., urine protein electrophoresis or serum protein electrophoresis). The albumin-to-nonalbumin ratio can aid in characterizing the pattern of protein abnormalities and guiding differential diagnosis.

In serum, nonalbumin refers to all plasma proteins other than albumin, including globulins and other acute-phase or transport proteins. The balance of albumin and nonalbumin components informs assessment of liver function, nutritional status, and immune activity.