| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letters |
1
Laboratoire de Biochimie, Hôpital Nord, and,
2
Laboratoire de Biochimie, Hôpital Bellevue, CHU-Hôpitaux de Saint-Etienne, 42055 Saint-Etienne Cedex 2, France
a Address correspondence to this author at: Laboratoire de Biochimie, Faculté de Médecine, 15 Rue Ambroise Paré, 42023 Saint-Etienne Cedex 2, France. Fax 33-4-77-42-14-89; e-mail frey{at}univ-st-etienne.fr
To the Editor:
Interference by monoclonal IgM has been described in the
immunonephelometric assays of C-reactive protein, antistreptolysin O,
ferritin, and complement C4 (1)(2)(3)(4)(5)(6). This report describes
the interference by monoclonal IgM (IgM
) in the
immunonephelometric assays of apolipoproteins A-I and B,
haptoglobin, and immunoglobulins A and G.
The patient, a man 54 years of age, was admitted to a cardiac care unit
with angina. His total plasma protein was 110 g/L, his serum
cholesterol was 3.3 mmol/L, his apolipoprotein A-I was 1.5 g/L, and his
apolipoprotein B was 2 g/L. Myeloma was suggested by the increase in
total plasma proteins and verified by immunonephelometric assay of
immunoglobulins and by immunofixation electrophoresis (Beckman
reagents), which identified a monoclonal IgM. This monoclonal IgM
was not a cryoglobulin because after 8 days at 4 °C, no flocculation
was observed in the serum sample.
The apolipoproteins, immunoglobulins, and haptoglobin were assayed
initially by immunonephelometry with a BNA and a BN II (Behring
Nephelometer; Dade-Behring) and on a second sample with a BN 100 and
again with a BN II. The BN II is operated at 37 °C, the others at
room temperature (~23 °C). The results are shown in Table 1
. The BNA (room temperature) appeared to overestimate all
proteins except IgM (2.94 g/L), which was underestimated in the crude
serum; after the crude serum was diluted, the IgM concentration was 60
g/L. The serum cholesterol value was consistent for apolipoproteins A-I
and B with the BN II (37 °C) procedures but not with the room
temperature methods.
|
To determine the frequency of this interference by monoclonal immunoglobulins, a double-blind study was conducted that involved determining the proteins with both a BN 100 and a BN II. Among 70 sera with monoclonal immunoglobulins (38 with monoclonal IgM, 12 with monoclonal IgA, 20 with monoclonal IgG), comparable interference occurred only for the index patient (Table 1B).
We therefore conclude that the monoclonal IgM could influence the BNA and BN 100 procedures. We (5) and others (1)(2)(3)(4)(6) have reported interference between monoclonal IgM and latex particles in the immunonephelometric assay of C-reactive protein, antistreptolysin O, and ferritin. However, latex particles and supplement reagents for precipitation were not used in the immunoglobulin and haptoglobin assays by the BNA, BN 100, or BN II procedures. This rules out any dependent unselective precipitation of the reagents.
Thus, after excluding a cryoglobulin and the reagents as causal factors
of the discrepancy in the presented data, we must conclude that the
monoclonal IgM was the primary reason for the present unselective
precipitation during the immunonephelometric assays of proteins,
which did not occur when the temperature was increased to 37 °C. We
point out the difficulty in taking into account this rare interference
because it occurred only once among 38 samples containing monoclonal
IgM checked in our laboratory.
References
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
