Measurement repeatability profiles of eight frequently requested measurands in clinical chemistry determined by duplicate measurements of patient samples

Figures & data

Table 1. Number of duplicate observations (rounded down to the nearest hundred) within the interval indicated in the parenthesis.

Measurand	Number
Alanine amino transferase (ALT) (0.1–16.7 µkat/L)	16,000
Aspartate amino transferase (AST) (0.05–16.7 µkat/L)	21,700
Calcium (1.25–3.75 mmol/L)	64,600
Cholesterol (1.29–15.5 mmol/L)	12,000
Creatinine (9–1,700 µmol/L)	75,000
CRP (3.1–60 mg/L)	21,600
Triglycerides (0.02–11.3 mmol/L)	18,300
Thyroid stimulating hormone (TSH) (0.05–100 mU/L)	23,900

Table 2. Number observations in each of the partitions analyzed by the ANOC. Concentration intervals as in Figure 3.

	ALT	AST	Calcium	Cholesterol	Creatinine	CRP	TG	TSH
1	12,409	1,793	17,320	3,093	2,491	2,603	17,149	5,306
2	5,299	9,637	16,830	3,093	11,008	4,969	5,761	2,243
3	6,173	10,179	17,957	6,969	23,462	3,700	6,111	4,968
4	3,541	17,559	11,854	6,699	21,237	2,558	5,009	5,249
5	3,999	3,685	1,244	2,807	16,933	10,098	2,225	5,983

Figure 1. Repeatability profiles based on 10 sets of1,000 duplicates. Absolute uncertainty (SS) are shown on the left Y-axis, relative uncertainty on the right axis. The X-axis shows the partitions (1–5), the corresponding concentration intervals are reported in Table 2. Error bars represent the IQR.

Figure 2. Repeatability profiles based on 30 sets of 25 duplicates. Absolute uncertainty (SD) are shown on the left Y-axis, relative uncertainty on the right axis. The X-axis shows the average concentration of the partitions. The concentration of the fifth partition has been selectively reduced to make the diagrams more readable. Error bars represent the IQR.

Table 3. The medians and 25- and 75 percentiles of results calculated from 10 repeated selections of 1,000 unique results. The minimal differences are based on the repeatability standard deviation in each partition.

	ALT					AST					Calcium					Cholesterol
	Conc	Freq	Median	25-P	75-P	Conc	Freq	Median	25-P	75-P	Conc	Freq	Median	25-P	75-P	Conc	Freq	Median	25-P	75-P
SD	0.3	36.6	0.012	0.012	0.013	0.2	14.4	0.015	0.013	0.016	2.1	26.3	0.023	0.022	0.023	3	12.9	0.06	0.05	0.06
	0.4	17.3	0.013	0.012	0.014	0.3	25.0	0.014	0.014	0.015	2.15	11.5	0.022	0.021	0.022	4.5	28.2	0.08	0.07	0.08
	0.6	19.1	0.013	0.013	0.014	0.4	19.3	0.015	0.014	0.016	2.25	29.6	0.022	0.022	0.022	5.5	25.6	0.08	0.08	0.09
	0.9	10.9	0.014	0.013	0.015	0.7	22.5	0.017	0.015	0.018	2.45	29.8	0.024	0.022	0.024	6.9	25.6	0.10	0.10	0.11
	15	16.1	0.029	0.026	0.036	20	18.8	0.025	0.021	0.033	3.2	2.9	0.028	0.028	0.030	10	7.7	0.13	0.12	0.13
%CV			6.1	5.9	6.5			10.1	9.3	11.4			1.2	1.1	1.2			2.2	2.2	2.3
			3.9	3.5	4.2			5.9	5.8	6.1			1.0	1.0	1.0			1.9	1.8	2.0
			2.7	2.6	3.0			4.3	4.1	4.7			1.0	1.0	1.0			1.7	1.6	1.8
			2.0	1.8	2.1			3.5	3.2	3.9			1.0	1.0	1.0			1.6	1.6	1.7
			1.2	1.2	1.3			1.7	1.5	2.1			1.1	1.1	1.2			1.7	1.7	1.8
MD			0.02	0.0	0.03			0.03	0.0	0.03			0.05	0.0	0.05			0.1	0.1	0.1
			0.03	0.0	0.03			0.03	0.0	0.03			0.04	0.0	0.04			0.2	0.1	0.2
			0.03	0.0	0.03			0.03	0.0	0.03			0.04	0.0	0.04			0.2	0.2	0.2
			0.03	0.0	0.03			0.03	0.0	0.04			0.05	0.0	0.05			0.2	0.2	0.2
			0.06	0.1	0.07			0.05	0.0	0.07			0.06	0.1	0.06			0.3	0.2	0.3
	Creatinine					CRP					Triglycerides					TSH
SD	50	7.7	2.5	2.3	2.8	7	20.4	0.5	0.3	0.5	1.1	19.6	0.11	0.07	0.16	0.7	20.5	0.01	0.01	0.01
	70	25.6	2.6	2.6	2.8	12	20.1	0.8	0.8	0.9	1.4	20.4	0.06	0.05	0.08	1.1	19.4	0.02	0.01	0.02
	85	22.9	2.8	2.7	2.9	20	21.7	1.0	0.9	1.1	1.8	21.5	0.04	0.04	0.05	1.55	20.6	0.02	0.02	0.02
	110	21.8	2.9	2.8	3.0	35	19.3	0.9	0.8	1.1	2.6	19.9	0.11	0.09	0.23	2.75	21.7	0.03	0.03	0.03
	500	22.0	3.2	3.1	3.2	75	18.5	1.3	1.3	1.5	10	18.6	0.18	0.11	0.20	20	17.9	0.11	0.11	0.12
%CV			6.4	6.0	7.0			7.3	5.9	7.4			6.2	4.8	7.3			1.8	1.7	1.9
			4.4	4.2	4.4			7.9	7.6	8.4			3.8	3.2	4.9			1.7	1.6	1.7
			3.6	3.5	3.7			6.9	6.3	7.6			2.6	2.5	3.3			1.6	1.6	1.7
			3.0	3.0	3.1			3.3	2.8	3.8			6.0	4.0	7.3			1.6	1.5	1.7
			2.0	1.9	2.1			2.8	2.6	3.3			4.4	1.9	5.7			1.6	1.6	1.6
MD			5.0	4.6	5.6			0.9	0.7	1.1			0.21	0.1	0.32			0.02	0.0	0.02
			5.2	5.2	5.5			1.6	1.5	1.8			0.12	0.1	0.16			0.03	0.0	0.03
			5.5	5.4	5.8			1.9	1.8	2.1			0.09	0.1	0.11			0.04	0.0	0.04
			5.8	5.7	5.9			1.7	1.5	2.1			0.22	0.2	0.45			0.07	0.1	0.07
			6.3	6.2	6.4			2.6	2.5	3.0			0.36	0.2	0.41			0.23	0.2	0.23

Table 4. The medians and interquartile intervals were based on 30 groups of 750 pairs of observations after randomization of the initial dataset.

	ALT				AST				Calcium				Cholesterol
	Conc	Median	25-perc	75 perc	Conc	Median	25-perc	75 perc	Conc	Median	25-perc	75 perc	Conc	Median	25-perc	75 perc
SD	0.2	0.011	0.010	0.013	0.07	0.015	0.013	0.018	2.1	0.023	0.021	0.025	3.0	0.055	0.051	0.061
	0.35	0.012	0.011	0.013	0.2	0.013	0.013	0.016	2.15	0.023	0.020	0.024	3.7	0.068	0.061	0.074
	0.5	0.012	0.011	0.013	0.3	0.013	0.012	0.016	2.25	0.023	0.021	0.025	5.0	0.077	0.065	0.088
	0.75	0.013	0.012	0.015	0.75	0.015	0.013	0.019	2.45	0.026	0.024	0.030	6.3	0.102	0.081	0.115
	1.8	0.021	0.018	0.026	1.8	0.025	0.019	0.034	2.8	0.030	0.028	0.031	6.9	0.127	0.115	0.145
%CV	0.2	5.90	5.23	6.31	0.07	12.57	11.77	15.12	2.1	1.14	1.03	1.28	3.0	2.21	1.97	2.37
	0.35	4.60	4.41	5.35	0.2	6.50	5.90	7.79	2.15	1.06	0.93	1.13	3.7	1.74	1.55	1.92
	0.5	3.26	2.80	3.42	0.3	4.49	4.01	5.31	2.25	0.97	1.06	1.14	5.0	1.56	1.32	1.76
	0.75	2.17	1.90	2.51	0.75	2.89	2.45	3.75	2.45	1.06	0.99	1.23	6.3	1.62	1.35	1.89
	1.8	1.29	1.21	1.39	1.8	0.90	0.86	1.03	2.8	1.14	1.03	1.20	6.9	1.74	1.54	1.96
	Creatinine				CRP				Triglycerides				TSH
SD	30	2.315	2.112	2.889	5.0	0.242	0.195	0.290	1.5	0.041	0.029	0.068	0.7	0.008	0.007	0.009
	45	2.674	2.287	2.990	7.5	0.405	0.333	0.552	1.8	0.038	0.028	0.052	0.9	0.014	0.012	0.016
	70	2.585	2.260	2.918	12.5	0.827	0.607	0.964	2.5	0.042	0.038	0.076	1.3	0.021	0.018	0.023
	95	2.668	2.437	2.943	17.5	0.856	0.660	1.034	3.5	0.048	0.041	0.076	2.1	0.030	0.027	0.034
	110	2.977	2.628	3.565	20.0	1.035	0.788	1.393	4.0	0.066	0.061	0.090	4.0	0.107	0.077	0.130
%CV	30	7.14	6.44	8.20	5.0	5.59	4.72	6.69	1.5	3.81	2.72	4.75	0.7	1.83	1.62	1.95
	45	5.36	4.65	5.94	7.5	5.27	4.51	6.80	1.8	2.18	1.65	2.99	0.9	1.62	1.39	1.72
	70	3.73	3.34	4.16	12.5	6.83	4.84	8.41	2.5	1.71	1.57	3.69	1.3	1.57	1.42	1.78
	95	2.90	2.62	3.24	17.5	5.39	3.94	6.63	3.5	1.42	1.23	2.37	2.1	1.53	1.38	1.65
	110	1.86	1.73	2.08	20.0	2.52	2.15	3.48	4.0	1.29	1.18	1.61	4.0	1.54	1.33	1.79

Figure 3. Repeatability profiles generated by ANOC analysis of the entire database.