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Test Code C4BPROTEIN C4B, Binding Protein

Performing Laboratory

Esoterix Endocrinology


Enzyme-linked immunosorbent assay (ELISA)

Reference Values

50 - 130%



Turnaround time: 2 - 7 days

Test Classification and CPT Coding


Computer Interface Code

PDM # 5601085

Physician Office Specimen Requirements

Container/Tube:  Light blue-top (3.2% sodium citrate) tube

Specimen:  Full tube or if delayed 1 mL plasma (0.5mL min)

Transport Temperature:  Refrigerate whole tube or preferred Freeze plasma after separation.


Collection: Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio. The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used. When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube.

Used for

Confirmation and characterization of protein S (PS) deficiency: C4b-binding protein elevates as an acute phase protein that may lead to enhanced protein S binding and decreased free protein S levels.