Table 1.

Basic characteristics and DKK1 serum level in the analysed cohorts

References	PsA pts included (n)	Female sex (n; %)	Age (years)	Disease duration (years)	Control pts included (n)	Method of serum DKK1 measurement	DKK1 level in PsA group*	DKK1 level in comparative group#
Daousiss [51]	15	7 (46.6%)	45.4 (± 7.2)	8.0 (4.0–14.0)	45—AS 45—RA 50—HC	DuoSet ELISA kit (R&D Systems)	2.44 ± 0.26 ng/ml	AS (↑) RA ( ↔) HC ( ↔)
Dalbeth [56]	38	16 (42.0%)	50.0 (26.0–68.0)	10.0 (0.5–45.0)	10—PsC 12—HC	ELISA. R&D duoset	2.98 (1.16–5.91) ng/ml	Ps(↓) HC (↓)
Jadon [58]	127 pPsA 117 PsSpA	61 (48.0%)—pPsA 43 (36.7%)—PsSpA	58.5 (50.3–66.6)—pPsA 59.5 (59.6–66.5)—PsSpA	15.0 (7.0–26.0)—pPsA 18.0 (9.0–27.0)—PsSpA	157—AS 200—PsC 50—HC	Quantikine ELISA kits (R&D systems)	3.03 (1.93–3.69) ng/ml—pPsA 3.34 (2.43–4.44) ng/ml -PsSpA	AS + PsSpA (↑)$ AS (↑)&
Fassio [34]	33	33 (100.0%)	58.8 (± 8.8)	< 3 years (inclusion criterion)	28—RA 35 HC	ELISA (Biomedica)	0.50 ± 0.34 ng/ml	RA (↑) HC (↑)
Fassio [35]	28	18 (64.3%)	57.0 (± 10.0)	< 3 years (inclusion criterion)	43—HC	ELISA (Biomedica)	0.52 ± 0.35 ng/ml	HC (↑)
Diani [59]	50	11 (22.0%)	48.0 (28.0–79.0)	2.1 (0.3–9.2)	50—PsC 20—HC	ELISA (Quantikine, R&D Systems Inc.)	2.80 (2.02–3.53) ng/ml	Ps( ↔) HC (↓)
Chung [60]	69	39 (56.5%)	52.7 (± 13.0)	5.0 (1.6–13.0)	39—RA 21—HC	ELISA kit (Cloud-Clone Corp.)	9.27 ± 3.28 ng/ml	RA (↓) HC (↓)
Abd el Hamid [61]	45	30 (66.7%)	42.2 (± 6.6)	5.0 (1.5–10.0)	45—HC	ELISA kit (Thermo Fischer Scientific)	9.09 (4.89–14.0) ng/ml	HC (↓)

AS ankylosing spondylitis, HC healthy controls, pPsA peripheral psoriatic arthritis, PsA psoriatic arthritis, Ps psoriasis, PsSpA psoriatic axial spondyloarthropathy, pts patients, RA rheumatoid arthritis

*For better comparison of DKK1 serum levels between studies original units were converted to ng/ml. The original values and units are present in text

^#The arrows indicate the relative level of DKK1 in comparative group with regard to the PsA group

^$Compared to pPsA group

^&Compared to PsSpA group