Test | No of paired samples | Paired t-test | Correlation | Bland Altman | Reference range of test | Interchangeably in clinical setting based Paired t-test p>0.05 | Interchangeably in clinical setting based on r>0.8 | Interchangeably in clinical setting based on small Bias OR max 10% difference between tests | Point scoring for clinical acceptability | ||||||||
Mean of difference | SD | SEM | 95% CI | Two-tailed p value | r (or rs) | 95% CI | Bias (%) | SD of bias (%) | 95% limits of agreement (%) | ||||||||
From | To | ||||||||||||||||
Hb | 30 | −0.20 | 11.49 | 2.10 | −4.49 to 4.09 | 0.9247 | 0.73 | 0.50 to 0.86 | 0.12 | 8.15 | −15.9 | 16.1 | 115–151 g/L | Yes | No | No | 1 |
WCC | 29 | −0.69 | 1.16 | 0.22 | −1.14 to −0.25 | 0.0033 | 0.92 | 0.83 to 0.96 | 7.88 | 12.99 | −17.59 | 22.34 | 5.1–11.4×109/L | No | Yes | No | 1 |
Platelets | 30 | 38.67 | 39.80 | 7.27 | 23.80 to 53.53 | <0.0001 | 0.93 | 0.86 to 0.97 | −15.79 | 16.96 | −49.03 | 17.44 | 147–397×109/L | No | Yes | No | 1 |
HbA1c (%) | 31 | −0.05 | 0.20 | 0.03 | −0.12 to 0.026 | 0.2024 | 0.98 | 0.97 to 0.99 | −0.80 | 3.43 | −5.92 | 7.53 | 4.0%–6.0% | Yes | Yes | Yes | 3 |
HbA1c (IFCC) | 32 | −0.47 | 2.05 | 0.36 | −1.20 to 0.27 | 0.2024 | 0.99 | 0.97 to 0.99 | 1.21 | 5.44 | −9.46 | 11.88 | 20–42 mmol/mol | Yes | Yes | No | 2 |
Sodium | 36 | −2.22 | 2.57 | 0.43 | −3.09 to −1.35 | <0.0001 | 0.80 | 0.64 to 0.90 | 1.57 | 1.81 | −1.98 | 5.13 | 133–146 mmol/L | No | No | Yes | 2 |
Potassium | 18‡ | −1.45 | 0.94 | 0.22 | −1.92 to −0.98 | <0.0001 | 0.75 | 0.44 to 0.90 | 27.77 | 14.19 | −0.05 | 55.48 | 3.5–5.3 mmol/L | No | No | No | 0 |
Urea | 36 | −0.77 | 0.55 | 0.09 | −0.96 to 0.58 | <0.0001 | 0.96 | 0.93 to 0.98 | 14.46 | 10.15 | −5.43 | 34.35 | 2.5–7.8 mmol/L | No | Yes | No | 1 |
Creatinine | 36 | −9.14 | 14.38 | 2.40 | −14.00 to 4.27 | 0.0005 | 0.83 | 0.69 to 0.91 | 11.63 | 17.89 | −23.43 | 46.70 | 60–120 umol/L | No | Yes | No | 1 |
Bilirubin | 59 | −0.41 | 0.85 | 0.11 | −0.63 to 0.18 | 0.0005 | 0.98 | 0.97 to 0.99 | 5.88 | 10.38 | −14.47 | 26.23 | 0–20 umol/L | No | Yes | No | 1 |
ALP | 59 | 4.10 | 55.92 | 7.28 | −10.47 to 18.68 | 0.2561 | 0.89 | 0.82 to 0.93 | 1.61 | 19.90 | −37.39 | 40.61 | 30–130 U/L | Yes | Yes | No | 2 |
ALT | 59 | −0.70 | 3.66 | 0.48 | −1.65 to 0.26 | 0.7827 | 0.98 | 0.97 to 0.99 | 2.75 | 13.20 | −23.12 | 28.62 | 8–40 IU/L | Yes | Yes | No | 2 |
Total protein | 58 | 0.26 | 2.92 | 0.38 | −0.51 to 1.03 | 0.5032 | 0.86 | 0.78 to 0.92 | −0.37 | 3.92 | −8.07 | 7.32 | 60–80 g/L | Yes | Yes | Yes | 3 |
Total IgE | 35 | 12.23 | 34.98 | 5.91 | 0.21 to 24.24 | 0.7104 | 0.99 | 0.99 to 1.00 | −34.87 | 69.23 | −170.6 | −100.80 | 3–150 IU/mol | Yes | Yes | No | 2 |
Vit D | 26‡ | −0.89 | 12.72 | 2.50 | −6.02 to 4.25 | 0.7258 | 0.90 | 0.78 to 0.95 | −7.26 | 53.68 | −112.5 | 97.96 | 50–75 nmol/L—adequate >75 nmol/L—optimal | Yes | Yes | No | 2 |
CRP | 37 | 1.00 | 4.89 | 0.80 | −0.63 to 2.63 | 0.2213 | 0.99 | 0.99 to 1.00 | −0.41 | 4.30 | −8.83 | 8.00 | <100 mg/L | Yes | Yes | Yes | 3 |
Albumin* | 59 | 0.00† | 0.4070 | 0.75 | −0.61 to 0.85 | −0.22 | 6.15 | −12.27 | 11.84 | 35–50 g/L | Yes | No | No | 1 |
Values in bold symbolise significant difference between the tests by p<0.05, poor correlation (r or rs<0.8), or wide limits of agreement.
Point scoring of clinical acceptability—refer to figure 1 for algorithm for determination of clinical acceptability of capillary test.
Mean, SD, SEM, CI, r, rs, % bias, % limits of agreement to two decimal places).
Bias is the average of the differences between the two methods of blood sampling, expressed as a percentage %.
HbA1c here expressed as a percentage (%) and as a value in mmol/mol (IFCC unit).
*Non-parametric statistics applied for non-Gaussian distribution: Wilcoxon matched pairs signed rank test, non-parametric Spearman correlation rs.
†Result represents median of difference and not mean.
‡Only 50% of potassium capillary samples were analysed due to haemolysis, and 72% of vitamin D capillary samples were analysed with the rest not processed due to insufficient blood in the capillary sample to process.
ALP, alkaline phosphatase; ALT, alanine transferase; CI, confidence interval; CRP, C reactive protein; Hb, haemoglobin; HbA1c, glycated haemoglobin; IgE, Immunoglobulin type E; r, Pearson’s correlation coefficient; rs, Spearman’s Rank correlation coefficient; SD, Standard deviation; SEM, SE of the mean of the difference; WCC, white cell count.