This method may be useful when:
(1) a patient is on heparin and the blood sample will not clot
(2) a plasma sample is available and a serum sample cannot be drawn (patient not available, patient difficult to collect)
The method does not affect the concentrations of immunoglobulins or light chains. It removes all of the fibrinogen as well as a small amount of albumin, alpha globulins and beta globulins. Therefore, the total protein needs to be measured after the treatment.
Method:
(1) Absolute ethanol is added to the sample in a ratio of 100 mL in 1 liter of treated sample. This is equivalent to 0.1 mL in 1 mL of treated sample.
(2) The sample is then treated in the cold, either (a) incubation in an ice bath for 15 minutes or (b) overnight refrigeration at 4°C.
(3) The specimen is then centrifuged with a chilled rotor at 4°C at 1100 g for 5 minutes.
(4) The supernatant is decanted.
(5) The total protein in the supernatant is determined.
(6) Protein electrophoresis is performed.
amount of immunoglobulin in grams =
= (total protein in supernatant) * (density as percent of total density in the electrophoresis strip)
Alternative methods for removing fibrinogen:
(1) antifibrinogen antibodies
(2) addition of thrombin
(3) with heparinized samples, protamine sulfate plus thrombin
