Table 5.
Typical flagging rates for the first measurement in outpatient adults (18–60 y) for 11 chemistry analytes.
| Analyte | Flag rate at LRL (%) | Flag rate at URL (%) | Comments |
|---|---|---|---|
| Sodium | 2.5 | 1 | Hypernatraemia is generally uncommon. |
| Potassium | 1 | Generally 2.5 | Higher flag rates may reflect pre-analytical issues e.g. sample transport or haemolysis. |
| Chloride | 1 | <1 | |
| Bicarbonate | 2.5 | <2.5 | Low values by Abbott assay. Manufacturer is recalibrating assay. |
| Creatinine | 2.5 | Generally 2.5 | Higher rates may reflect the problem in removing disease from hospital databases. |
| Calcium | 2.5 | Variable; low in men and premenopausal women; 3.2 % in postmenopausal women. | Reference interval of 2.10–2.60 mmol/L accommodates lot-to-lot calibrator variability. There is no loss of sensitivity of detection of primary hyperthyroidism in postmenopausal women when using 2.60 mmol/L as the URL. |
| Phosphate | 1.5 | 2.5 | Hypophosphataemia was uncommon and probably appropriate to its clinical importance. |
| Magnesium | 5 | 1 | Hypomagnesaemia was more common than expected. The Aussie Normals study had a different cut-off of 0.77 mmol/L. The reference interval is reported to broaden with age.19 |
| Lactate Dehydrogenase | Low | Commonly >2.5 | Vitros and DxC assays have higher low flag rates but this may not be clinically significant. |
| Alkaline Phosphatase | <1 | 7–10 | The benefit of using the URL of 110 U/L is to detect pathology in postmenopausal women. Increasing the URL to 115 U/L had negligible impact because of the logarithmic distribution of values. |
| Total Protein | <2.5 | <3.5 | Rounding of LRL from 62 to 60 g/L was for convenience. Flagging of calculated globulins may detect immune deficiency better. |
LRL, lower reference limit; URL, upper reference limit.