Refractometry: This method is used for estimating plasma protein (including fibrinogen) in EDTA plasma and is reported on routine hemograms at Cornell University. It measures the refractive index of a sample relative to the refractive index of water. The reading is actually a measurement of total solids and is only an estimate of protein concentration, since variation in other serum components "solids" (sodium, chloride, phosphate, glucose, cholesterol, urea, etc.) also can affect refractive index. Lipemia and moderate to severe hemolysis renders the results invalid.
Biuret Method: This is the colorimetric method used on the automated chemistry analyzer. It detects all proteins and is accurate for the range of 1-10 g/dl. It is not sensitive enough for low concentrations found in some body fluids such as CSF, urine, and many body cavity effusions.
Note that the total protein (as measured by refractometer) provided with the hemogram is usually higher than that provided from the chemistry analyzer. This is due to:
Note that urinary dipsticks can be used to estimate protein in CSF samples, however they are not as accurate as turbidometric techniques.