Table 3.
Proportion of patients who are misclassified when laboratory testing for diabetes is repeated (American Diabetes Association criteria).
| Tests | True classification | Classification after repeated tests | Without bias (%) | With positive bias (%) | With negative bias (%) |
|---|---|---|---|---|---|
| Fasting Plasma Glucose Biological variation: 5.7% Analytical variation: 2.5% | Normal (<5.6 mmol/L) | Normal | 91.5 | 70.5 | 98.7 |
| Impaired | 8.5 | 29.4 | 1.3 | ||
| Diabetes | 0 | 0 | 0 | ||
| Impaired (5.6–6.9 mmol/L) | Normal | 25.3 | 6.1 | 54.3 | |
| Impaired | 71.6 | 81.3 | 45.3 | ||
| Diabetes | 3.1 | 12.6 | 0.5 | ||
| Diabetes (≥7 mmol/L) | Normal | 0 | 0 | 0.1 | |
| Impaired | 10.5 | 2.4 | 24.1 | ||
| Diabetes | 89.5 | 97.6 | 75.8 | ||
| OGTT Biological variation: 16.7% Analytical variation: 2.5% | Normal (<7.8 mmol/L) | Normal | 91.5 | 85.5 | 95.4 |
| Impaired | 8.5 | 14.4 | 4.6 | ||
| Diabetes | 0 | 0.1 | 0 | ||
| Impaired (7.8–11.0 mmol/L) | Normal | 26.9 | 17.4 | 37.8 | |
| Impaired | 61.7 | 62.7 | 56.1 | ||
| Diabetes | 11.4 | 19.9 | 6.1 | ||
| Diabetes (≥11.1 mmol/L) | Normal | 1 | 0.5 | 1.8 | |
| Impaired | 15.9 | 10.3 | 22.1 | ||
| Diabetes | 83.1 | 89.2 | 76.1 | ||
| HbA1c Biological variation: 1.8% Analytical variation: 2% | Normal (<5.7%) | Normal | 86.8 | 66.3 | 98.1 |
| Pre-diabetes | 13.2 | 33.7 | 1.9 | ||
| Diabetes | 0 | 0 | 0 | ||
| Pre-diabetes (5.7–6.4%) | Normal | 17.2 | 4.9 | 44.3 | |
| Pre-diabetes | 80.6 | 88.3 | 55.4 | ||
| Diabetes | 2.2 | 6.8 | 0.3 | ||
| Diabetes (≥6.5%) | Normal | 0 | 0 | 0 | |
| Pre-diabetes | 10.3 | 3 | 25.1 | ||
| Diabetes | 89.7 | 97 | 74.9 | ||
| HbA1c Biological variation: 1.8% Analytical variation: 3.5% | Normal (<5.7%) | Normal | 81.3 | 64.2 | 94.3 |
| Pre-diabetes | 18.7 | 35.8 | 5.7 | ||
| Diabetes | 0 | 0 | 0 | ||
| Pre-diabetes (5.7–6.4%) | Normal | 22.3 | 10.1 | 44.4 | |
| Pre-diabetes | 73.7 | 80.2 | 54.6 | ||
| Diabetes | 4 | 9.7 | 1 | ||
| Diabetes (≥6.5%) | Normal | 0 | 0 | 0.1 | |
| Pre-diabetes | 12.9 | 5.9 | 24.9 | ||
| Diabetes | 87.1 | 94.1 | 75 |
A between-laboratory positive bias of +7% and +2.5% were introduced for the fasting plasma glucose/oral glucose tolerance test, and HbA1c, respectively. A between-laboratory negative bias of −6% and −3% were introduced for the fasting plasma glucose/oral glucose tolerance test, and HbA1c, respectively.