International Journal of Clinical Medicine, 2013, 4, 99-101 Published Online February 2013 (
Low Levels of Complement Factor C4 Not Always
Implicate Disease Activity in Systemic Lupus
E. J. ter Borg1, H. van Velzen-Blad2, D. Hamann3
1Department of Internal Medicine and Rheumatology, St. Antonius Hospital Nieuwegein/Utrecht, Nieuwegein, The Netherlands;
2Department of Clinical Immunology, St. Antonius Hospital Nieuwegein/Utrecht, Nieuwegein, The Netherlands; 3Department of
Immunopathology and Blood Coagulation, Sanquin Diagnostics, Amsterdam, The Netherlands.
Email:, h.vv elzen@ a,
Received October 21st, 2012; revised November 22nd, 2012; accepted November 30th, 2012
A lupus patient with a clinically quiescent disease stage will be described who had severely depressed C4 levels while
levels of C3 en CH50 were normal. Additional testing revealed a homozygous C4A isotype deficiency as the cause of
the very low C4 levels. It should be emphasized that in SLE, a (very) low C4 level does not always means (subclinical)
disease activity.
Keywords: Complement; Homozygous C4A Isotype Deficiency; Systemic Lupus Erythematosus
1. Introduction
Disease activity in systemic lupus erythematosus usually
is monitored by serially measurements of anti-dsDNA [1]
and C3/4 levels [1-3]. When levels of C3 and/or C4 fall,
the clinician has to be extra alert for a flare up of disease.
Complement factor C4 exists as two main isotypes: C4A
and C4B, encoded by two closely linked genes. The C4
gene copy number varies from 2 - 6, but i t is mostly 4 [4].
Inherited deficiencies of complement components C1-
4 are associated in nearly 50% with SLE [5]. Partial C4
deficiency has been associated with SLE, the most com-
mon being C4A deficiency [5,6] and susceptibility to
bacterial infection (C4B, [7]). In lupus, the prevalence of
homozygous C4A deficiency has been reported between
10.2% - 22.2% in white patients [5]. Homozygous defi-
ciency of C4A has been reported to occur in 5.8% in
healthy lab workers [8].
It has been postulated that C4A deficiency leads to
impaired clearance of immune complexes, explaining its
association with immune complex diseases [5].
2. Case
A 45-year-old female was admitted because of a sym-
metric rheumatoid-factor negative polyarthritis, treated
by diclofenac by the general practitioner. Her previous
history included a hysterectomy, lumbar hernia nuclei
pulposi and a depression one year before admission.
Since one month she experienced generalized joint pains
with morning stiffness. Physical examination showed
polyarthritis with fever up to 38.5˚ Celsius, cervical
lymphadenopathy and a rash. Her admission was com-
plicated by a short p eriod o f atrial fibrillatio n . Lab oratory
findings (see Table 1): ESR 90 mm/first hour, CRP at
maximum 42 mg/l (normal <5 mg/l), normal blood
counts, WBC-differentiation and renal function. Transa-
minases were disturbed probably by the use of diclofenac:
ASAT 325 IU /L, ALAT 50 0 I U/L w ith normal v alu es fo r
AF, GGT and CPK. Urine analysis showed slight pro-
teinuria (600 mg/l) with a normal sediment. ANA were
Table 1. Some laboratory examinations at admission.
Item Measured value Normal value
ESR 90 mm/first hour <12 mm/first hour
CRP 42 mg/l <5 mg/l
ANA 1: >640 Negative
Anti-dsDNA 742 IU/ml Negative
C3 109 mg/dl 90 - 180 mg/dl
C4 <6 mg/dl 15 - 40 mg/dl
CH50 94 % 75% - 125%
C4A <0.1 mg/dl 3.5 - 23 mg/dl
C4B 6.6 mg/dl 2.8 - 22 mg/dl
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Low Levels of Complement Factor C4 Not Always Implicate Disease Activity in Systemic Lupus Erythematosus
strongly positive (1: >640; IIF on HEP2 cells) as were
anti-dsDNA antibodies (Farr assay; 742 IU/ml).
A diagnosis was made of (idiopathic) active systemic
lupus erythematosus (SLE) and the patient was treated
with 1000 mg methylprednisolone iv followed by oral
prednisone 40 mg a day with a good clinical response
while proteinuria disappeared and CRP levels normalized.
After stopping diclofenac transaminases normalized. After
dismission prednisone was gradually tapered to 5 mg a
day and hydro xyc hl o r oquine 400 m g a day was ad ded .
Two weeks after admission complement C3 was 109
mg/dl (90 - 180 mg/dl) and C4 < 6 mg/dl (15 - 40 mg/dl).
CH50 was normal (94%; normal values 75% - 125%).
During follow up, levels of C3 always were normal as
was CH50 whereas C4 was persistently strongly de-
creased (<6 mg/dl), however without signs of clinical
disease activity. Anti-dsDNA became and remained
negative up to 2010. In 2010 there were no signs of
clinical disease activity using prednisone 5 mg a day.
3. Complement Assays
The activity of the classical pathway (CH50) was deter-
mined according to Meyer [9] and expressed as a per-
centage of the serum pool of 30 healthy donors. The
concentrations of the complement factors C3 and C4
were measured by an immunoturbidimetric assay on a
Cobas Fara autoanalyser.
4. Additional Examinations of Complement
C4A level was below detection li mit (<0.1 mg/d l; normal
range 3.5 - 23 mg/dl) and C4B level was 6.6 mg/dl (nor-
mal range 2.8 - 22 mg/dl) as measured by ELISA [8].
MPLA (Multiplex Ligation-dependent Probe Amplifica-
tion, 9) revealed the presence of 2 C4B genes and com-
plete absence of C4A genes.
5. Discussion
Our case with SLE had persistently severely depressed
C4 levels during a long lasting quiescent disease stage
while C3 levels were normal as was CH50. Complement
assays were at first performed two weeks after admission
when lupus activity had largely decreased.
In spite of the very low C4 concentration , CH50 activ-
ity was within the normal range. This indicates that suf-
ficient functional C4 was present for complement activi-
tion by the classical pathway. Additional analyses show-
ed no C4A, but a normal C4B level resulting in a low
total C4 concentration . So , in SLE decreased lev els of C4
not always implicate disease activity, in casu comple-
ment consumption.
Heterozygous and homozygous deficiencies of C4A
have been reported in 40% - 60% of SLE patients from
almost all ethnic groups or races investigated (reviewed
in Ref. [6]). Hence, a persistently low C4 level might be
frequently misinterpreted in SLE.
It has been reported that lupus patients with homozy-
gous C4A deficiency have other disease characteristics
than heterozygous lupus patients. Petri et al for example
found a reduced frequency of seizures and proteinuria in
homozygous lupus patients [5]. Indeed, our patient did
not have significant proteinuria nor seizures.
6. Conclusion
we suggest to look for inherited complement deficiencies
in case of severely depressed levels of C4 in lupus pa-
tient without signs of clinical disease activity and/or nor-
mal values of C3 and CH50. When, in such a case, a
C4A isotype deficiency is found, this complement com-
ponent cannot be used to monitor disease activity in SLE.
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Low Levels of Complement Factor C4 Not Always Implicate Disease Activity in Systemic Lupus Erythematosus
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