International Journal of Clinical Medicine, 2013, 4, 13-19
Published Online December 2013 (http://www.scirp.org/journal/ijcm)
http://dx.doi.org/10.4236/ijcm.2013.412A2003
Open Access IJCM
13
Differences in Acute Phase Reactants between Gout and
Pseudogout
Clement E. Tagoe1*, Yasmin Raza2
1Department of Medicine, Albert Einstein College of Medicine, Bronx, USA; 2Department of Medicine, Temple University, Phila-
delphia, USA.
Received October 2nd, 2013; revised November 1st, 2013; accepted November 25th, 2013
Copyright © 2013 Clement E. Tagoe, Yasmin Raza. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited. In accordance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of
the intellectual property Clement E. Tagoe, Yasmin Raza. All Copyright © 2013 are guarded by law and by SCIRP as a guardian.
ABSTRACT
Objectives: To define clinical differences in the acute phase response and serum acute phase reactants between gout,
pseudogout and crystal-induced arthritis in the presence of non-articular infections (CAI). Patients and Methods:
Eleven patients with definite gout, 12 patients with pseudogout and 5 patients with CIA were included in the study.
Results: The erythrocyte sedimentation rate (ESR) was significantly different between gout (68.2 ± 49.9 mm/Hr) and
CIA (113.8 ± 37.2 mm/Hr) but not between gout and pseudogout (83.9 ± 45.6 mm/Hr) or between pseudogout and CIA.
The C-reactive protein (CRP) was significantly increased between gout (10.1 ± 7.9 mg/dL) and pseudogout (18.9 ± 9.8
mg/dL), gout and CIA (36.5 ± 12.4 mg/dL) as well as between pseudogout and CIA. The peripheral white cell count
was significantly different between gout (9.27 ± 3.7 k/μL) and CIA (16.5 ± 6.8 k/μL), and between pseudogout (8.9 ±
3.2 k/μL) and CIA. Conclusions: Measurement of ESR and CRP are helpful in crystal-induced arthritis. The CRP has
more discriminating utility than the ESR in distinguishing between gout, pseudogout and CIA. Peripheral wbc is most
useful for differentiating crystal-induced arthritis from CIA.
Keywords: Gout; Pseudogout; Crystal-Induced Arthritis; Acute Phase Reactants; C-Reactive Protein; Calcium
Pyrophosphate Dihydrate Deposition Disease
1. Introduction
The crystal-induced arthropathies are a group of diseases
with a broad range of clinical manifestations from asymp-
tomatic to severely inflammatory. The most common
presentations at the inflammatory end of the disease
spectrum are gout and pseudogout, precipitated by intra-
articular monosodium urate monohydrate (MSUM) and
calcium pyrophosphate dihydrate (CPPD) crystals re-
spectively [1]. Both conditions have very high preva-
lence [2-5]. The resulting health care costs and loss of
productivity to society are quite considerable [6].
Gout and pseudogout are highly inflammatory forms
of arthritis associated with the release of proinflamma-
tory cytokines through a variety of pathways including
the activation of inflammasomes in neutrophils, macro-
phages and other cell types [7]. However, there are dif-
ferences in the way that MSUM and CPPD crystals re-
spectively activate the inflammasome in the quality and
quantity of cytokine release. The massive systemic re-
lease of inflammatory cytokines causes fever, chills,
malaise and the cardinal signs of inflammation locally
including tumor, dolor and rubor, which can make the
discrimination of crystal-induced arthritis from septic ar-
thritis, cellulitis and other infectious causes difficult to
impossible, at least earlier in the presentation. Further-
more, the typical crystal arthropathy patient generally has
multiple comorbidities, which adds to the difficulty in
establishing a diagnosis and guiding management. Se-
rum acute phase reactants have been suggested as useful
tools for refining the diagnosis. It is generally accepted
that the erythrocyte sedimentation rate (ESR) and C-
reactive protein (CRP) are most useful for differentiating
infectious from non-infectious causes.
We sought to define the characteristics of gout and
*Corresponding author.

Differences in Acute Phase Reactants between Gout and Pseudogout
Open Access IJCM
14
pseudogout in terms of the acute phase response to see if
the ESR and CRP remained useful in discriminating be-
tween crystal arthropathy and infection and whether there
were any differences in the behavior of those acute phase
reactants between gout and pseudogout.
2. Patients and Methods
The study was retrospective and included patients admit-
ted to the institution between 2004 and 2012 with defi-
nite crystal-induced arthritis from whom there was aspi-
ration of synovial fluid for microbiological, chemical and
crystal analysis. Gout was diagnosed using the American
college of rheumatology (ACR) diagnostic criteria [8].
Pseudogout was diagnosed by the criteria of McCarty as
modified by the European League Against Rheumatism
(EULAR) [9,10].
2.1. Inclusion Criteria
Eleven subjects with acute gout were included in the
study. All gout patients had hyperuricemia and the pres-
ence of MSUM crystals in their joint aspirates. Patients
were included if they had definite pseudogout with
CPPD crystals isolated from the affected joint (10 pa-
tients) or if they had probable pseudogout (2 patients) in
the absence of all of the following; history of gout, per-
sistent hyperuricemia, tophi, radiographic changes suspi-
cious for gout and a non-inflammatory joint aspirate. All
patients had negative synovial fluid gram stain and cul-
ture. To study the effects of non-articular infections on
the serum acute phase reactants five patients with defi-
nite gout (3 patients) and definite pseudogout (2 patients),
in the presence of acute infections were included in the
study. Hemoglobin levels were >10g/dL in all patients.
2.2. Exclusion Criteria
Patients with acute infections or who had received anti-
biotics during the hospitalization were excluded from the
gout and pseudogout groups. Any subjects with a diag-
nosis of a well-defined connective tissue disease, positive
serum rheumatoid factor, positive serum anti-citrulli-
nated protein antibody (ACPA), positive serum anti-nu-
clear antibody (ANA), chronic infections such as osteo-
myelitis, active HIV infection or active hepatitis were
excluded from the study. One patient with joint aspirates
showing both MSUM and CPPD crystals was analyzed
separately.
Serum acute phase reactants, specifically ESR and
CRP obtained within 24 hours of the joint aspiration
were considered representative of the gout or pseudogout
event. When multiple values were found the results clos-
est to the date and time of aspiration were selected and
were invariably the highest values present in such cases.
Peripheral white cell count, serum creatinine and serum
uric acid were available from the date of joint aspiration
as part of the work up for crystal-induced arthritis. Ra-
diographic data from within six months of the admission
date were examined for characteristic features of gout or
pseudogout including the presence of chondrocalcinosis.
The presence of erosions suspicious for gout, in the pres-
ence of pseudogout, led to exclusion from the study.
2.3. Statistical Analysis
Descriptive statistical analyses using the mean, standard
deviation, range and median of variables were employed.
Mann-Whitney U-test was used for the pair-wise com-
parison of means. Group means were compared by one-
way Analysis of Variance (ANOVA). Correlations of sta-
tistical significance between groups were done using
Spearman Rank Correlation. A P-value < 0.05 was con-
sidered to be significant.
3. Results
3.1. Patient Characteristics
Eleven patients with definite gout had a mean age of 62.3
± 10.7 years and were predominantly male (73%). The
pseudogout patients (n = 12) were significantly older,
with a mean age of 78 ± 9.3 years and an equal male to
female sex ratio (1:1) (Table 1). Body mass index (BMI)
trended towards statistical significance between gout and
pseudogout patients at 31.1 ± 5.7 kg/m2 and 25.4 ± 6.0
kg/m2 respectively (Table 1). Serum uric acid levels
were significantly higher in gout than in pseudogout pa-
tients, 11.4 ± 3.5 mg/dL and 6.0 ± 1.7 mg/dL respec-
tively. The serum creatinine was higher in gout patients
Table 1. Gout and pseudogout patient demographics, serum uric acid, serum creatinine, peripheral white blood cell count
and synovial fluid white cell count expresse d as mean ± SD (range) median, unless otherwise stated. *Significant at P < 0.05.
Gout (n = 11) Pseudogout (n = 12) P-value
Age (years) 62.3 ± 10.7 (38 - 77) 67 78 ± 9.3 (61 - 88) 78 0.002*
Sex (male/female) 8/3 6/6 0.292
BMI (kg/m2) 31.1 ± 5.7 (23 - 41.4) 31.3 25.4 ± 6.0 (16.7 - 35.9) 24.5 0.056
Serum uric acid (mg/dL) 11.4 ± 3.5 (6.2 - 16.9) 11.8 6.0 ± 1.7 (2.9 - 8.3) 6.2 0.001*
Serum creatinine (mg/dL) 1.5 ± 0.5 (0.9 - 2.5) 1.4 1.3 ± 0.7 (0.6 - 2.9) 1.2 0.205
Peripheral wbc (k/μL) 9.27 ± 3.7 (5.3 - 18.3) 7.6 8.9 ± 3.2 (2.1 - 13.8) 9.3 0.877
Synovial wbc (cells/μL) 13,133 ± 12,196 (1100 - 41,550) 8800 14,790 ± 21,419 (1225 - 80,000) 8150 0.859

Differences in Acute Phase Reactants between Gout and Pseudogout
Open Access IJCM
15
but not significantly so. The peripheral white blood cell
count (wbc) and synovial fluid wbc were not statistically
different between gout and pseudogout patients (Table
1).
3.2. Differences in ESR and CRP between Gout,
Pseudogout and Crystal-Induced Arthritis
with Non-Articular Infection (CIA)
There was no significant difference between the ESR in
acute gout (68.2 ± 49.9 mm/Hr) and pseudogout (83.9 ±
45.6 mm/Hr) (Table 2). However there was a significant
difference between the ESR in gout and CIA (113.8 ±
37.2 mm/Hr) (Table 2). By contrast the CRP levels in
both gout (10.1 ± 7.9 mg/dL) and pseudogout (18.9 ± 9.8
mg/dL) were significantly different from the levels in
CIA (36.5 ± 12.4 mg/dL). There was also a significant
difference in CRP between gout and pseudogout by pair-
wise comparison. The overall trend was for higher levels
of CRP and ESR in pseudogout than in gout and for
higher levels of both in CIA than in pseudogout (Figures
1(a) and (b) respectively). Of note a single female patient
aged 65 years with both MSUM and CPPD crystals
showed a peripheral wbc of 15.1 k/μL, BMI of 21.9
kg/m2, synovial wbc of 24,200 cells/μL, serum uric acid
level of 11.4 mg/dL, serum creatinine of 2.8 mg/dL, CRP
of 40 mg/dL and ESR of 115 mm/Hr. Joint aspirate
showed the presence of both MSUM and CPPD crystals.
There was radiographic evidence of chondrocalcinosis as
well.
3.3. Correlation of Peripheral wbc and Synovial
wbc with ESR and CRP in Gout and
Pseudogout
There was no significant correlation between the ESR
and the CRP in gout patients with the peripheral wbc or
synovial wbc levels (Table 3). Neither did ESR correlate
with CRP in pseudogout patients. There was a trend to
statistical significance between the peripheral wbc in
Table 2. (a) Pair-wise comparison of means for ESR and CRP in A/D. gout, B/E. pseudogout and C/F. CIA patients using
Mann-Whitney U-test. *Significant at P < 0.05; (b) Comparison of group means by ANOVA. *Significant at P < 0.05.
(a)
ESR P-value for pair-wise comparison of ESR means
A. Gout ESR 68.2 ± 49.9 (5 - 122) 73 B. Pseudogout ESR 83.9 ± 45.6 (20 - 140) 88.5C. CIA ESR 113.8 ± 37.2 (50 - 140) 124
A vs B 0.230
A vs C 0.041*
B vs C 0.169
CRP P-value for pair-wise comparison of CRP mea ns
D. Gout CRP 10.1 ± 7.9 (0.3 - 24.7) 8.7 E. Pseudogout CRP 18.9 ± 9.8 (5.8 - 32.8) 15.4F. CIA CRP 36.5 ± 12.4 (16.7 - 45.2) 43.5
D vs E 0.037*
D vs F 0.003*
E vs F 0.020*
(b)
ANOVA P-value
ESR 0.2067
CRP 0.0001*
(a) CRP (b) ESR
Figure 1. Comparison of CRP and ESR between gout, pseudogout and CIA. Error bars represent mean ± S.D. Statistical
differences are summarized in Table 2. NS = not significant.

Differences in Acute Phase Reactants between Gout and Pseudogout
Open Access IJCM
16
gout and the gout CRP with a P-value of 0.052 (Table 3).
These results suggest that the peripheral and synovial cell
counts are of little utility in differentiating between gout
and pseudogout.
3.4. Comparison of Peripheral wbc and Synovial
wbc between Gout, Pseudogout and CIA
There was a significant difference between the peripheral
wbc in gout and CIA (Table 4). There was also a sig-
nificant difference between the peripheral wbc in pseu-
dogout and CIA (Table 4). However, there was no sig-
nificant relationship between the levels of synovial wbc
comparing gout and CIA, or between pseudogout and
patients with CIA (Table 4). This suggests that marked
elevations of the peripheral wbc are more suggestive of
the presence of infection than of the existence of crystal-
induced arthritis. It also suggests that unlike the case in
septic arthritis the presence of infection at a non-articular
site probably does not significantly influence the syno-
vial wbc [11].
4. Discussion
We have examined the relationship between the acute
phase response and the acute phase reactants, ESR and
CRP in acute gout and pseudogout. We have compared
those responses in patients with acute gouty arthritis or
pseudogout in the presence or absence of non-intra-ar-
ticular infections. Patients with gout were significantly
younger than pseudogout patients, were more likely to be
male and had higher levels of serum uric acid. There was
a trend to higher BMI in the gout patients echoing find-
ings observed in population studies [12]. The association
of renal impairment with gout was reflected by the higher
serum creatinine in the gout patients though this was not
statistically significant perhaps because of the small sam-
ple size (Table 1). The congruence of these observations
with reported findings suggests that the patient sample
though small was fairly representative of the larger gout
and pseudogout populations.
There was a significant difference between the levels
of ESR in gout and CIA but not between the gout-ESR
and pseudogout-ESR. However, there was a significant
difference between the CRP in gout and pseudogout and
more so between gout and CIA (Table 2). This incre-
mental difference was similar to that seen with the ESR
but additionally was statistically significant (Figure 1).
There were no positive clinical correlations between
peripheral or synovial cell counts and ESR or CRP in
gout and pseudogout (Table 3). By contrast there was a
significant correlation between the peripheral wbc in both
gout and pseudogout, and the peripheral wbc in patients
with gout or pseudogout in the presence of an infection
(Table 4). This suggests that in crystal-induced arthritis
there is a rise in CRP that is not associated with a propor-
tional rise in the peripheral wbc, i.e. there is a CRP-pe-
ripheral wbc dissociation in crystal-induced arthritis, par-
ticularly in pseudogout. In addition, the synovial wbc is
only helpful when there is intra-articular infection and
cannot distinguish between gout and pseudogout [11].
However the single patient with mixed crystal arthritis
and a peripheral wbc of 15.1 k/μL might suggest that
gout with pseudogout may be associated with significant
peripheral wbc elevations. However the current study did
not have enough patients to make a definitive determina-
tion and the finding calls for further study.
Table 3. Correlation of peripheral wbc and articular wbc with ESR and CRP in gout and pseudogout. Significant at P < 0.05.
Correlation Spearman r P value
Gout peripheral wbc with gout ESR 0.207 0.514
Gout peripheral wbc with gout CRP 0.606 0.052
Pseudogout peripheral wbc with pseudogout ESR 0.364 0.246
Pseudogout peripheral wbc with pseudogout CRP −0.336 0.287
Gout articular wbc with gout ESR 0.335 0.385
Gout articular wbc with gout CRP 0.301 0.437
Pseudogout articular wbc with pseudogout ESR −0.210 0.514
Pseudogout articular wbc with pseudogout CRP 0.154 0.635
Table 4. Comparison of gout and pseudogout peripheral wbc and articular wbc with peripheral wbc and articular wbc in
CIA. *Significant at P < 0.05.
Gout (n = 11) Pseudogout (n = 12) CIA (Gout n = 3, Pseudogout n = 2) P values
(Gout vs CIA/Pseudogout vs CIA)
Peripheral wbc (k/μL) 9.27 ± 3.7 (5.3 - 18.3) 7.6 8.9 ± 3.2 (2.1 - 13.8) 9.316.5 ± 6.8 (9.1 - 27.1) 14.3 0.023*/0.020*
Synovial wbc (cells/μL) 13,133 ± 12,196
(1100 - 41,550) 8800
14,790 ± 21,419
(1225 - 80,000) 8150
29,580 ± 23,320
(6700 - 67,200) 25,100 0.182/0.073
Infection diagnoses
Cellulitis 3
Pneumonia 1
Urinary tract infection 1

Differences in Acute Phase Reactants between Gout and Pseudogout
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Possible reasons for the differences in the acute phase
response, ESR and CRP between acute gout and pseu-
dogout could be explained by differences in their cyto-
kine profiles. Several studies suggest that the release of
interleukin-1β (IL-1β) from monocytes is similar between
gout and pseudogout, suggesting equal activation of the
inflammasome [13,14]. However, significant differences
may exist in the release of interleukin-6 (IL-6) as sug-
gested by data from Guerne et al [15]. Release of IL-6
from monocytes stimulated in vitro with CPPD crystals
was more than seen with MSUM crystals although a
higher concentration of the former crystals was required
for peak IL-6 levels. Hydroxyapatite crystals were the
least vigorous in stimulating IL-6 secretion [15]. The
authors also demonstrated IL-6 release from synovio-
cytes and showed that both MSUM and CPPD cause re-
lease of IL-6 into the synovial fluid. Work by Liu et al
[16] suggested that there was differential release of in-
terleukin-8 (IL-8) by monocytes stimulated with MSUM
or CPPD crystals with the latter causing significantly
more IL-8 release. The clinical relevance of IL-8 may be
in the massive cellular recruitment that characterizes
pseudogout, which sometimes presents with the pseudo-
septic picture. It is not known if there are differences in
the release by monocytes and other cell types of inter-
leukin-1α upon stimulation by microcrystals although
such inflammasome-dependent release has been docu-
mented [17]. Other cytokines like tumor necrosis factor-α
(TNF-α) have been implicated in the inflammatory re-
sponse of monocytes and synoviocytes to microcrystals
[18]. Microcrystals are known to induce the differentia-
tion of monocytes to the active M1 phenotype that are
involved in the release of inflammatory cytokines [19].
C-reactive protein is produced predominantly by he-
patocytes under the influence of IL-1β and IL-6 [20].
Since the release of IL-6 is not inflammasome dependent
we speculate that IL-1β production leads to IL-6 release
in crystal-induced arthritis as a downstream event fol-
lowing inflammasome activation [19,21,22]. Various cell
types have inflammasomes including neutrophils, mono-
cytes, macrophages and synovial fibroblast-like cells and
are probably involved in the recognition of microcrystals
[23]. The higher levels of CRP in pseudogout could re-
flect higher release of IL-6 in pseudogout, acting in con-
cert with IL-1β on hepatocytes. Indeed Desgeorges et al.
[22] demonstrated that patients with chondrocalcinosis
had higher levels of both synovial fluid IL-6 and soluble
IL-6 receptor-α than osteoarthritis patients and had levels
comparable to patients with gout or rheumatoid arthritis.
Serum levels of those molecules were also elevated [22].
The study did not specify whether chondrocalcinosis pa-
tients had active pseudogout at the time of joint aspira-
tion, or osteoarthritis with the isolation of CPPD crystals
from joint aspirates. Therefore it is difficult to conclude
where on the CPPD disease spectrum they were. How-
ever, one could speculate that IL-6 release may pre-
dominate in pseudogout causing the differential rise in
CRP. This could be due in part to the negative regulatory
influence of IL-6 in gout [24]. It could also be due to the
modulation of transforming growth factor-β (TGF-β) and
other anti-inflammatory cytokines produced by M2 macro-
phages since TGF-β may have a permissive role in pseu-
dogout and CPPD disease distinct from its purely anti-
inflammatory role in gout [25,26]. This could lead to a
prolongation of the proinflammatory influence of IL-6 in
pseudogout.
Regardless of the precise mechanism by which CRP is
increased in pseudogout, it is possible that its release is
augmented in the presence of mixed microcrystals. One
patient had both MSUM and CPPD crystals with a sig-
nificant elevation of CRP of 40 mg/dL. However the
single patient did not allow for any definite conclusions
and further studies are needed. In conclusion, our study
suggests differences in the acute phase response between
gout and pseudogout, which might aid in diagnosis. The
absence of similar findings by Söderquist et al. may be
explained by their failure to separate gout from pseu-
dogout [27]. We think that marked elevations of periph-
eral wbc should alert the clinician to the presence of in-
fection. We also believe that significant elevations in
CRP particularly in the absence of corresponding eleva-
tions in peripheral wbc should suggest pseudogout over
gouty arthritis. Lastly we would recommend extreme
vigilance for mixed microcrystal deposits or the presence
of sepsis in patients with both marked elevations in pe-
ripheral wbc and CRP. Marked elevations in synovial
wbc remain the most useful marker of septic arthritis
[11].
5. Study limitations
The study is limited by the small sample size and there-
fore might not be representative of the larger population.
In addition, the study was retrospective. However, the
small size may have increased the threshold for statistical
significance and suggest that the positive findings may
hold up in a larger study. However, these findings will
need to be verified in a larger prospectively designed
study.
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