The table below, though by no means exhaustive, represents some of the common drug interferences encountered in tests requested in the department. Drug effects may be biological or analytical. In the former, a real in vivo change in the analyte occurs, not usually directly related to the desired therapeutic effect of the drug.
| Test | Interferant | Effect |
Biological/ Analytical |
| ALP |
anticonvulsants, barbiturates, oral contraceptives EDTA contamination |
Increase Decrease |
B A |
| Calcium |
venous stasis, Vit D pregnancy, citrate EDTA contamination |
Increase Decrease Decrease Decrease |
B B B/A A |
| Cholesterol | oestrogens | Decrease | B |
| Glucose |
frusemide, thiazides, corticosteroids, oestrogens, stress Vit C, storage |
Increase Decrease |
B A |
| GGT | anticonvulsants, barbiturates, alcohol | Increase | B |
| Potassium |
insulin, corticosteroids, diuretics amiloride, antineoplastic agents haemolysis, EDTA contamination, storage |
Increase Decrease Increase |
B B A |
|
Prolactin |
oestrogens, MAO inhibitors, cimetidine | Increase | B |
| Sodium |
Lithium diuretics, carbamazepine lipaemia |
Increase Decrease Decrease |
B B A |
| Thyroxine |
amiodarone, pregnancy, oestrogens phenytoin, corticosteroids autoantibodies |
Increase Decrease Decrease |
B B A |