Frequently Encoutered Interferences in Selected Analytes
Clinical
Biochemistry

The table below, though by no means exhaustive, represents some of the common 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 therapeutic effect of the drug.
Test Interferent Effect Analytical (A)
Biological (B)
Alkaline phosphatase anticonvulsants, barbiturates, oral contraceptives
EDTA contamination
Increase
Decrease
B
A
Calcium venous stasis, Vitamin D
pregnancy
citrate
EDTA contamination
Increase
Decrease
Decrease
Decrease
B
B
B/A
A
Cholesterol oestrogens
Decrease B
Glucose frusemide, thiazides, corticosteriods,
oestrogens,stress
Vitamin C, storage
Increase

Decrease
B

A
gammaGT anticonvulsants, barbiturates, alcohol Increase B
Potassium insulin, corticosteroids, diuretics
amiloride, antineoplastic agents
haemolysis, EDTA contamination, storage
Decrease
Increase
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
heterophilic antibodies
Increase
Decrease
Decrease
B
B
A