Table 1.

Interlab variability of quantity versus fold-change measurements in the same samples

A Quantity
sample	site				mean	stdev	cv
	1	2	3	4
67	116.6	337.4	276.5	120.9	213	111	52
285	641.6	2,635.5	2,103.6	869.2	1562	961	62
50	7,812.3	34,844.6	24,100.8	11,655.7	19603	12311	63
139	12,670.9	45,624.4	32,626.6	14,999.1	26480	15565	59
886	13,819.6	42,753.6	37,017.4	17,014.2	27651	14379	52

B Fold-change
sample	site				mean	stdev	cv
	1	2	3	4
67	1.0	1.0	1.0	1.0
285	5.5	7.8	7.6	7.2	7.0	1.0	14.9
50	67.0	103.3	87.2	96.4	88.5	15.7	17.8
139	108.7	135.2	118.0	124.1	121.5	11.1	9.1
886	118.6	126.7	133.9	140.7	130.0	9.5	7.3

Expression of CXCL9 in 5 urine cDNA samples isolated from CTOT-01 study subjects was measured by qPCR. Samples and TaqMan assays were prepared and distributed from site 1. Master mix and real-time instrument varied by site (table S1). Four sites submitted results for this experiment and no data points were omitted. A) CXCL9 quantity determined by each site with mean, standard deviation and percent CV. B) Fold-change of each sample relative to sample 67 (Qty_sampleX/Qty_sample67). The inter-laboratory variation (CV) for fold-change measurements was lower (7–18%) than for quantity measurements (52–63%). The same pattern was seen for the other target genes in urine and blood samples.