DB immunoassays

DB immunoassays (see Supplemental Tab. 1, http://www.vai.org/vari/labs/haab. asp) were performed on a Behring Nephelometer (BN) II (2.2/D, serial no. 330135) and on a Dimension (DIM) RxL (serial no. 970933-AX) from DB (Deerfield, IL) with the HUPO PPP specimens [8]. Most tests performed are approved by the Food and Drug Administration (FDA) only for serum samples, as outlined in the manufacturer data sheets. Tests for ferritin (FERR), soluble transferrin receptor (sTfR), cardiac troponin I (cTNI), and myoglobin (MYO) on the Dimension system are also approved for heparinized plasma. Tests for C-reactive protein (CRP), IgE, b2-micro-globulin, and MYO on the BN system are also approved for EDTA and heparinized plasma. The creatine kinase MB (mass assay, MMB), human chorionic gonadotropin (HCG), and thyroid stimulating hormone (TSH) assays are FDA-approved for use in serum, EDTA-plasma, and heparin-plasma samples. The fibrinogen, plasminogen, antithrombin III, and fibronectin tests are approved only for EDTA- and citrate-plasma samples, not for serum. In case test formats were not compatible with a sample type (e.g., fibrinogen in serum), data were not considered.

Two assay systems were used at DB: the BN and the Dimension methods. Both are rapid, specific, precise, and accurate [9-11]. For each analysis, appropriate Dade Behring standards, calibrators, and controls were utilized, along with a PSA control from Bio-Rad Laboratories (Hercules, CA). These standards are based on highly purified proteins and/or common international reference materials (IRMs) [1214]. BN systems are dedicated protein analyzers that apply either antiserum or particle-enhanced immunonephelometric quantitation of analytes [10, 15]. Pro-

Tab. 1 Number of individual assays with consistent maxima or minima in each preparation type for each data set. Each column gives the number of proteins for a given preparation method that showed a maximum (top) or minimum (bottom) value in that preparation method for every sample and every replicate. Total number of assays in each data set is given in the right column

Data set

Citrate

EDTA

Heparin

Serum

Total

Total assays

Maxima

DB

0

0

2

10

12

33

GNF

1

13

3

4

21

88

MS]

0

10

0

9

19

168

VAR]

0

1

4

1

3

28

Total

1

24

9

24

55

317

Minima

DB

24

0

0

1

25

33

GNF

4

1

0

3

8

88

MS]

0

1

2

1

4

168

VAR]

3

0

0

0

3

28

Total

31

2

2

5

40

317

teins in the human sample form immune complexes with specific particle-bound or antiserum antibodies. These complexes scatter a beam of light, with intensity proportional to the relevant protein concentration. Dimension methods on routine clinical analyzers are enzyme immunoassays based on the "sandwich" principle. A sample incubated with chromium dioxide particles coated with an mAb and a conjugate reagent labeled mAb specific for the protein to be analyzed forms a particle/protein/conjugate sandwich. Unbound conjugate is removed by magnetic separation and washing. The sandwich bound conjugate enzyme triggers an amplification cascade, which produces a colored product [9].

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