A rapid, accurate, precise assay for determination of plasma transferrin

Plasma transferrin (TFN) levels are valid as markers of protein-calorie malnutrition (PCM). Current methods for determining TFN, specifically, radial immunodiffusion (RID) plates or derivation from total iron-binding capacity (TIBC), are relatively expensive, time consuming (20-50 hr) and technically demanding, limiting the use of TFN levels in the routine screening for PCM. A rapid (60-90 min), accurate and precise TFN assay, easily performed with common laboratory equipment, was developed for use in a study of hospitalized patients. This assay requires 15 microliter of plasma and is based on an antigen-antibody reaction using commercially available TFN antibody. After a 30-min incubation, turbidity is measured at 413 nm on a spectrophotometer with a 1-cm path length. Values by this method are linear over the range of 50-760 mg/dl. Plasma samples (n = 72) were assayed for TFN by this turbidimetric (TURB) technique and the standard RID technique. Correlation between the two assays was r = 0.942 over the range of TFN = 81-403 mg/dl (TFNRID = 30.7 + (0.931) TFNTURB). Coefficient of variation (CV) for TFNTURB was 4.0%. RID kit insert reports a CV = 2.9% at a value of 380 mg/dl. This assay overcomes many of the difficulties associated with TFN determination by RID or derived from TIBC and may allow more widespread application of plasma TFN levels as a clinically relevant PCM screening tool.