Table 3.
Examples of laboratory calculations and the rules to be used for evaluating uncertainty in their respective output values as described in Table 2. As discussed in the text, the variables within each of the equations are assumed to be uncorrelated.
| Item | Function | Example equation | Measurand | Rule |
|---|---|---|---|---|
| 1 | y = x1 + x2 − x3 − x4 | AG = Na+ + K+ − Cl− − HCO3− | AG; anion gap, unit mmol/L. | 3 |
| 2 | y = Ax1 + x2 + x3+ B where A and B are without uncertainty | C Osmol = 1.86 (Na+) + urea + glucose + 9 | C Osmol; calculated serum osmolality, unit mmol/Kg. 17,18 | 3 |
| 3 | y =x1 − A(B − x2) = x1 − AB + Ax2 where A and B are without uncertainty | C Ca++ = Ca++ − 0.02 (40 − S albumin) | C Ca++; corrected serum calcium concentration, unit mmol/L. 19,20 | 3 |
| 4 | y = (x1 × x2) / (x3 × x4) | CrCl = (U × V) / (S × T) | CrCl; creatinine clearance, unit ml/min or ml/sec (depending on the units for T). | 8 |
| 5 | y = (x1 × x2) / (x3 × x4) | FEs = (Us × SCr) / (UCr × Ss) | FEs; fractional excretion of a substance, dimensionless quantity.34 | 8 |
| 6 | y = log10 x and y = log10xA = Alog10 x where A is without uncertainty | pH = − log10 [H+] = log10 [H+]−1 | pH definition; dimensionless quantity. | 15 |
| 7 | y = A + log10 (x1/x2) = A + log10 x1 − log10 x2 where A is without uncertainty | pH = pKa + log10 (base / acid) | pH; Henderson Hasselbalch equation assuming pKa has no uncertainty. | 17 |
| 8 | y = x1 + log10 (x2/x3) = x1 + log10 x2 − log10 x3 | pH = pKa + log10 (base / acid) | pH; Henderson Hasselbalch equation with an uncertainty estimate for pKa. | 1,17 |
| 9 | y = (ln x1 − ln x2) / (x3 − x4) | Kd = (ln C1 − ln C2) / (T2 − T1) | Kd = drug elimination rate constant, unit time−1.35 | 23 |
| 10 | y = (x1 / x2)A where A is without uncertainty | INR = (P / N)ISI | INR; international normalised ratio, dimensionless quantity. ISI; international sensitivity index. | 10 |
| 11 | y = a(b x1)D1× (c x2)D2 where D1 and D2 are without uncertainty | eGFR = 175 (SCr × 0.0113)−1.154 (age)−0.203 | eGFR; estimated GFR using MDRD/IDMS formula for males, units mL/min/1.73m2.30–33 | 24 |
| 12 | y = a(b x1)w1 × (c x2)w2 where w1 and w2 contribute uncertainty | eGFR = 175 (SCr × 0.0113)−1.154 (age)−0.203 | eGFR; estimated GFR using MDRD/IDMS formula for males, units mL/min/1.73m2.30–33 | 25 |
| 13 | y = (x1 / x2)w where w contributes uncertainty | INR = (P / N)ISI | INR; international normalised ratio, dimensionless quantity. ISI; international sensitivity index. | 20 |