Analytical performance and user-friendliness of five novel point-of-care D-dimer assays

Figures & data

Figure 1. Flowchart of study design.

Table 1. Imprecision data of the Point-of-Care (POC) D-dimer assays used in this study.

	Within-day variation^a				Between-day variation^b
POC D-dimer test system	Low mean in µg/L (range)	CV (%)	High mean in µg/L (range)	CV (%)	Low mean in µg/L (range)	CV (%)	High mean in µg/L (range)	CV (%)
Nano-Checker 710	249 (163–346)	26.1	1172 (1068–1297)	7.2	554 (409–610)	15.3	1662 (1496–1882)	9.1
AFIAS-1	304 (279–322)	6.0	893 (860–918)	2.6	384 (378–395)	1.8	1513 (1452–1609)	4.3
iChroma-II	331 (308–351)	5.8	815 (755–913)	9.3	363 (336–413)	9.0	1167 (1058–1266)	6.9
Standard F200	510 (497–518)	1.7	1815 (1727–1866)	3.0	766 (719–839)	6.8	2001 (1852–2148)	6.8
Hipro AFS/1	672 (620–740)	6.9	896 (840–970)	7.2	860 (780–1020)	11.1	2170 (2020–2240)	4.0

^a For this data D-dimer was measured 5 times within one day.

^b For this data D-dimer was measured once a day for 5 consecutive days.

Figure 2. Bland-Altman plots comparing Point-of-Care (POC) D-dimer results of (A) Nano-Checker 710, (B) AFIAS-1, (C) iChroma-II, (D) Standard F200, (E) Hipro AFS/1 assays with D-dimer results of our laboratory (lab) assay (STA-Liatest PLUS). The dotted lines indicate mean differences between POC assays and lab assays, while the dashed lines indicate their 95% confidence intervals. Corresponding values are presented in Table 2 (third column).

Table 2. Results of method comparison of five Point-of-Care D-dimer assays with the STA-Liatest PLUS.

	Pearson's r	Passing and Bablok regression line equation (slope, intercept)	Mean bias with STA-Liatest PLUS (μg/L)
Nano-Checker 710	0.73 (0.63–0.80)	y = −36.1 + 0.82x	−165 (−675 – +345)
AFIAS-1	0.93 (0.91–0.95)	y = 30.1 + 0.73x	−121 (−423 – +181)
iChroma-II	0.90 (0.87–0.93)	y = 67.1 + 0.57x	−147 (−559 – +264)
Standard F200	0.88 (0.84–0.91)	y = 31.9 + 1.07x	−53 (−278 – +384)
Hipro AFS/1	0.68 (0.58–0.75)	y = 66.6 + 1.09x	−69 (−503 – +641)

Data are presented as mean (95% confidence interval).

Significant deviations from y = x are presented in bold font.

Table 3. Concordance and discordance of all Point-of-Care assays versus the STA-Liatest PLUS assay. Data are based on dichotomous results (positive/negative) with a 500 μg/L cut-off value.

	Nano-Checker 710	AFIAS-1	iChroma-II	Standard F200	Hipro AFS/1
Concordance (%)^1	71.8 [73.5]	86.0 [91.3]	82.2 [88.5]	89.5 [92.4]	76.8 [82.1]
Discordance: STA+ POC− (%)^2	23.1 [15.4]	14.0 [5.8]	17.8 [7.5]	3.5 [4.7]	7.9 [11.3]
Discordance: STA− POC+ (%)^3	5.1 [11.1]	0.0 [2.9]	0.0 [4.0]	7.0 [2.9]	15.2 [6.6]

Values in square brackets are adjusted for slope and intercept of the corresponding Passing and Pablok regression line equation as presented in Table 2 (see discussion section). STA: STA-Liatest PLUS assay. POC: Point-of-care D-dimer assay as mentioned in the table.

1) % results that show both positive or negative results for STA and POC.

2) % results that show positive results for STA and negative results for POC.

3) % results that show negative results for STA and positive results for POC.

Table 4. Device characteristics and user-friendliness of Point-of-Care D-dimer devices used in this study.

Device	Nano-Checker 710	AFIAS-1	iChroma-II	Standard F200	Hipro AFS/1
Company	Nano-Ditech	Boditech	Boditech	SD Biosensor	Hipro Biotechnology
Size (d x w x h)	20.5 × 30 × 18 cm	32.5 × 18 × 20.5 cm	22 × 27.5 × 9 cm	26 × 21 × 20 cm	40.5 × 16 × 35 cm
Assay method	Lateral flow immunoassay	Lateral flow immunoassay	Lateral flow immunoassay	Lateral flow immunoassay	Immuno-turbidimetric assay
Plasma tube	Lithium heparin	Sodium citrate	Sodium citrate	Sodium citrate	Sodium citrate
Sample volume	5 µL	100/30^a µL	10 µL	10 µL	15 µL
Processing time	15 min	12 min	12 min	7 min	3 min
Number of pre-analytical steps^b	4	4 (C-tip: 3^a)	5	5	3
Number of different POC tests available^c^,^d	8	28	36	23	32
D-dimer whole blood sampling possible?	Yes	Yes	Yes	Yes	No^e
Microchip inserted in sample package?^f	No	Yes	Yes	No	No
SUS score^g (IQR)^h	70.0 (55.0 − 85.0)	65.0 (40.0 − 90.0)	37.5 (30.0 − 60.0)	57.5 (35.0 − 85.0)	75.0 (47.5–97.5)

^a For sample processing, we used 100 μL blood samples according to the package leaflet. For evaluating user-friendliness, we used a new method for capillary blood sampling (“C-tip”), requiring a 30 μL blood sample, because this tip was made available by then.

^b Examples of these steps: collecting blood, adding blood to buffer, mixing blood with buffer, adding sample to test system, loading and initializing sample for processing.

^c The following tests can be processed in all test systems in addition to D-dimer: (high-sensitive) C-Reactive Protein, NT-proBNP, Troponin I, CK-MB.

^d For many tests, a whole blood version is not (yet) available.

^e At the time of writing, a whole blood version was under development.

^f These microchips are different for each test and lot number, which is subject to error.

^g System Usability Scale. Whole blood samples were used for evaluating user-friendliness.

^h Interquartile range.