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