Urine Afamin and Afamin–Creatinine Ratio as Biomarkers for Kidney Injury

Figures & data

Table 1.  Clinical information of 376 participants.

Classifications	Age (years)^†
	Males, n	Females, n
Healthy volunteers (n = 247)	121 (49.0%)	126 (51.0%)	40.2 ± 14.4
PMN (n = 59)	31 (52.2%)	28 (47.5%)	53.0 ± 15.6
IgAN (n = 46)	22 (47.8%)	24 (52.2%)	38.3 ± 13.7
MCD (n = 24)	14 (58.3%)	10 (41.7%)	43.1 ± 20.1

^†Data were presented as means ± standard deviations.

IgAN: IgA nephropathy; MCD: Minimal change disease; PMN: Primary membranous nephropathy.

Table 2.  The repeatability and within-laboratory precisions.

Mean concentration (ng/ml)	Repeatability precision		Within-laboratory precision
	SD (ng/ml)	CV (%)	SD (ng/ml)	CV (%)
38.9	4.8	12.3	4.8	12.3
12.5	0.7	5.6	1.7	13.6
Manufacturer’s claims	–	10.0	–	12.0

CV: Coefficient of variation; SD: Standard deviation.

Figure 1.  The first-order model of four equally spaced concentrations in validation of linearity.

The solid line represents the linear model of four equally spaced concentration levels. Linear range of the method is 2.0–76.4 ng/ml. n = 3 per dilution level of the urine sample.

Figure 2.  Distribution of urine afamin and afamin–creatinine ratio in healthy individuals according to sex groups.

Box and whisker plots demonstrated gender-specific distributions of uAFM (A) and AfCR (B) in 121 males and 126 females. Mann–Whitney U test was used to compare differences between sex groups. The detail information was shown in Supplementary table 1.

*p < 0.05.

AfCR: Afamin–creatinine ratio; uAFM: Urine afamin.

Table 3.  The relationship between afamin-related variables (urine afamin and afamin–creatinine ratio) and age in two sex groups^†.

Sex groups	n	uAFM (ng/ml)		AfCR (μg/g)
		rs	p-value	rs	p-value
Males	121	-0.137	0.134	-0.047	0.612
Females	126	0.036	0.687	0.169	0.058

^†Spearman coefficient of rank correlation was used to compare the relationship.

AfCR: Afamin–creatinine ratio; uAFM: Urine afamin; r_s: Spearman’s rank correlation coefficient.

Table 4.  The detail results of study participants in the clinical evaluation study^†‡.

Gender	Study groups	n	uAFM (ng/ml)	AfCR (μg/g)	uALB (mg/l)	ACR (mg/g)
	Controls	121	32.2 (20.7–43.7)	26.2 (19.3–40.3)	4.57 (2.59–6.94)	3.92 (2.96–5.50)
Male:	PMN	31	37.3 (28.9–52.7)^§	40.9 (25.1–88.8)^§	2100.00 (817.00–3260.00)^§	2553.06 (837.78–4837.76)^§
	IgAN	22	44.4 (24.6–89.0)^§	71.0 (33.2–142.9)^§	334.00 (117.75–863.50)^§	381.78 (222.41–798.76)^§
	MCD	14	78.9 (32.7–237.3)^§	155.0 (70.6–304.3)^§	979.50 (246.75–3837.50)^§	4199.21 (481.03–5422.83)^§
	Controls	126	15.4 (5.5–9.9)	17.2 (8.0–26.6)	3.90 (2.19–6.22)	4.63 (3.54–6.29)
Female:	PMN	28	31.5 (19.5–53.6)^§	83.3 (42.4–145.2)^§	814.00 (432.00–1975.00)^§	2556.69 (1141.40–3367.80)^§
	IgAN	24	28.3 (15.5–52.5)^§	62.4 (38.6–95.0)^§	318.00 (77.60–630.25)^§	585.68 (298.41–1052.97)^§
	MCD	10	27.5 (18.9–32.0)^§	123.6 (31.2–166.1)^§	216.50 (45.70–3770.00)^§	1573.39 (230.62–6638.48)^§

^†Data were presented as medians (interquartile ranges).

^‡Mann–Whitney U test was used to compare differences between patients groups (PMN, IgAN or MCD) and controls.

^§p < 0.05.

ACR: Albumin–creatinine ratio; AfCR: Afamin–creatinine ratio; IgAN: IgA nephropathy; MCD: Minimal change disease; PMN: Primary membranous nephropathy; uAFM: Urine afamin; uALB: Urine albumin.

Figure 3.  Distribution of urine afamin and afamin–creatinine ratio in healthy volunteers and patients.

Box and whisker plots showed distribution of uAFM (A & C) and AfCR (B & D) in healthy volunteers (controls, n = 121 for males and 126 for females) compared with patients with PMN (n = 31 for males and 28 for females), IgAN (n = 22 for males and 24 for females) and MCD (n = 14 for males and 10 for females). Mann–Whitney U test was used to compare differences.

*p < 0.05.

ACR: Albumin-creatinine ratio; AfCR: Afamin–creatinine ratio; IgAN: IgA nephropathy; MCD: Minimal change disease; PMN: Primary membranous nephropathy; uAFM: Urine afamin.

Figure 4.  Area under the receiver-operating characteristic curve analysis of urine afamin, afamin–creatinine ratio, urine albumin and albumin–creatinine ratio in discriminating glomerulonephritis from healthy control.

ACR: Albumin–creatinine ratio; AfCR: Afamin–creatinine ratio; AUC: Area under the curve; uAFM: Urine afamin; uALB: Urine albumin.