INTERFERING SUBSTANCES
INTERFERING SUBSTANCES
This appendix lists known physiological (in vivo) interferences as well as analytical (in vitro) interferences that may occur with the
methodologies in use at LabCorp. While every effort is made to employ
methodologies that reduce interferences, inherent characteristics of certain
industry-standard methodologies are predisposed to physiological or analytical
interference. The data presented here are derived from the literature, as well
as from in-house studies. With appropriate patient preparation it is hoped that
the potential for these substances to cause erroneous results will be minimized.
Interfering Substances: Catecholamines
Plasma, Physiological (in vivo)
No Effect:
Indomethacin
Ramipril
Increase:
Ajmaline
Aminophylline
Chlorpromazine
Clonidine
Cocoa
Cyclopropane
Diazoxide
Epinephrine
Ethanol
Ether
Isoproterenol
MAO inhibitors
Methyldopa
Nitroglycerin
Perphenazine
Phenothiazines
Phentolamine
Promethazine
Stress
Decrease:
Captopril
Reserpine
Urine, Physiological (in vivo)
No Effect:
Acetaminophen
Amphetamine
Aspirin
Cannabis
Chlordiazepoxide
Chlorothiazide
Diazepam
Diphenhydramine
Ephedrin
Glucose
Hydralazine
Mecamylamine
Meprobamate
Muscular exercise
Oral contraceptives
Phenobarbital
Phentolamine
Increase:
Ethanol
Isoproterenol
Muscular exercise
Nicotine
Nitroglycerin
Pain
Prochlorperazine
Rauwolfia
Reserpine
Smoking
Stress
Syrosingopine
Theophylline
Decrease:
Clonidine
Decaborane
Diurnal variation
Guanethidine
Methyldopa
Ouabain
Radiographic agents
Reserpine
Sleep
Tosylate bretylium
Interfering Substance: Citrate
Urine, Physiological (in vivo)
No Effect:
Bedrest
Lithium
Increase:
Citrates
Parathyroid extract
Decrease:
Acetazolamide
Bendrofluazide
Cellulose phosphate
Chlorothiazide
Hydrochlorothiazide
Polythiazide
Thiazides
Interfering Substance: Cortisol, Free
Urine, Physiological (in vivo)
Increase:
Estrogens
Oral contraceptives
Sandfly fever
Decrease:
Ketoconazole
Lead
Interfering Substances: 17-Hydroxycorticosteroids
Urine, Analytical (in vitro)
No Effect:
Alclometasone
Amphetamine
Aspirin
Barbiturates
Chloramphenicol
Chlordiazepoxide
Dextroamphetamine
Nalidixic acid
Penicillin
Phenobarbital
Phenytoin
Propoxyphene
Quinine
Secobarbital
Increase:
Acetazolamide
Acetone
Antihypertensive agents
Ascorbic acid
Carbamazepine
Cefoxitin
Cephalothin
Chloral hydrate
Chlordiazepoxide
Chlormerodrin
Chlorothiazide
Chlorpromazine
Colchicine
Dexamethasone
Digitoxin
Digoxin
Erythromycin
Ethinamate
Etryptamine
Fructose
Glutethimide
Hydroxyzine
Iodides
Meprobamate
Methenamine
Methyprylon
Oleandomycin
Paraldehyde
Penicillin
Perphenazine
Phenazopyridine
Phenothiazines
Piperidine
Potassium iodide
Prochlorperazine
Promazine
Quinidine
Quinine
Spironolactone
Sulfamerazine
Testosterone
Tranquilizers
Vitamin K
Decrease:
Aspirin
Carbamazepine
Estrogens
Hydralazine
Phenytoin
Prochlorperazine
Promethazine
Reserpine
Salicylate
Urine, Physiological (in vivo)
No Effect:
Acetaminophen
Amobarbital
Aspirin
Barbiturates
Bedrest
Chlordiazepoxide
Clopamide
Cromoglycate
Diazepam
Diphenhydramine
Iothalamate
Nitrazepam
Phenobarbital
Smoking
Starvation
Increase:
Betamethasone
Chlorthalidone
Corticotropin
Cortisone
Diethylstilbestrol
Diurnal variation
Ethinyl estradiol
Gonadotropin
Histamine
Metyrapone
Muscular exercise
Sleep deprivation
Decrease:
Aminoglutethimide
Barbiturates
Blindness
Calcium gluconate
Carbon disulfide
Chlorpromazine
Corticosteroids
Corticotropin
Dexamethasone
Estrogens
Ethinyl estradiol
Lead
Levodopa
MAO inhibitors
Medroxyprogesterone
Meperidine
Methandrostenolone
Methylethinylestradiol
Metyrapone
Mitotane
Morphine
Norethynodrel
Oral contraceptives
Pentazocine
Perphenazine
Phenobarbital
Phenothiazines
Phenylbutazone
Phenytoin
Progesterone
Promazine
Propoxyphene
Rauwolfia
Reserpine
SKF-12218
Interfering Substance: Hydroxyindoleacetic Acid (5-HIAA)
Urine, Physiological (in vivo)
No Effect:
Amantadine
Barbiturates
Increase:
Avocados
Eggplant
Fluorouracil
Melphalan
Methamphetamine
Nicotine
Phenmetrazine
Pineapples
Plums
Pregnancy
Rauwolfia
Reserpine
Sleep deprivation
Smoking
Walnuts
Decrease:
Aging
Chlorophenylalanine
Corticotropin
Ethanol
Heparin
Hydrazine derivatives
Imipramine
Isocarboxazid
Isoniazid
Levodopa
MAO inhibitors
Methyldopa
Streptozocin
Interfering Substance: Serotonin (5-Hydroxytryptamine)
Plasma, Physiological (in vivo)
Increase:
Diurnal variation
MAO inhibitors
Decrease:
Methysergide
Reserpine
Blood, Physiological (in vivo)
No Effect:
Food
Interfering Substances: 17-Ketogenic Steroids
Urine, Analytical (in vitro)
No Effect:
Ampicillin
Carbamazepine
Chlorothiazide
Glutethimide
Increase:
Acetazolamide
Acetone
Acetophenon
Cephaloridine
Cephalothin
Chlordiazepoxide
Chlorpromazine
Digitoxin
Etryptamine
Hydralazine
Hydroxyzine
Meprobamate
Methyprylon
Nalidixic acid
Oleandomycin
Paraldehyde
Penicillin
Phenaglycodol
Phenazopyridine
Phenothiazines
Quinine
Spironolactone
Decrease:
Chlordiazepoxide
Glucose
Iodipamide
Iothalamate
Meprobamate
Metyrapone
Radiographic acid
Urine, Physiological (in vivo)
No Effect:
Carbamazepine
Iothalamate
Oxytocin
Increase:
Ampicillin
Cortisone
Metyrapone
Decrease:
Ampicillin
Dexamethasone
Oral contraceptives
Interfering Substances: 17-Ketosteroids
Urine, Analytical (in vitro)
No Effect:
Acetazolamide
Amphetamine
Ampicillin
Aspirin
Barbiturates
Chlordiazepoxide
Chlorothiazide
Dextroamphetamine
Digitoxin
Gentamicin
Glutethimide
Hydralazine
Hydroxyzine
Perphenazine
Phenobarbital
Phenytoin
Prochlorperazine
Propoxyphene
Testosterone
Increase:
Acetone
Acetophenone
Antihypertensive agents
Ascorbic acid
Cephaloridine
Cephalothin
Chloramphenicol
Chlorothiazide
Chlorpromazine
Cloxacillin
Dexamethasone
Erythromycin
Ethinamate
Etryptamine
Meprobamate
Methicillin
Methyprylon
Morphine
Nalidixic acid
Oleandomycin
Oxacillin
Penicillin
Phenaglycodol
Phenazopyridine
Phenothiazines
Piperidine
Quinidine
Reserpine
Secobarbital
Spironolactone
Tranquilizers
Decrease:
Carbamazepine
Chlordiazepoxide
Chlormerodrin
Digoxin
Estrogens
Glucose
Meprobamate
Metyrapone
Promazine
Propoxyphene
Reserpine
Secobarbital
Spironolactone
Urine, Physiological (in vivo)
No Effect:
Acetaminophen
Aspirin
Barbiturates
Carbamazepine
Chlordiazepoxide
Clopamide
Diazepam
Diphenhydramine
Iothalamate
Lead
Phenobarbital
Increase:
Aging
Ampicillin
Chlorpromazine
Chlorthalidone
Corticotropin
Danazol
Diurnal variation
Ethinyl estradiol
Gonadotropin
Muscular excercise
Nandrolone
Pregnancy
Testolactone
Decrease:
Aminoglutethimide
Ampicillin
Betamethasone
Blindness
Carbon disulfide
Chlorpromazine
Corticosteroids
Corticotropin
Cortisone
Fluoxymesterone
Menopause
Meperidine
Methandrostenolone
Metronidazole
Morphine
Noise
Oral contraceptives
Oxymetholone
Phenothiazines
Phenytoin
Probenecid
Propoxyphene
Pyrazinamide
Spironolactone
Interfering Substance: Metanephrine
Urine, Physiological (in vivo)
Increase:
Hydrazine derivatives
MAO inhibitors
Prochlorperazine
Decrease:
Levodopa
Urine, Analytical (in vitro)
Increase:
Buspirone (antianxiety)
Interfering Substance: Oxalate
Urine, Analytical (in vitro)
No Effect:
Ascorbic acid
Increase:
Ascorbic acid
Homogentisic acid
Decrease:
Ascorbic acid
Calcium carbamide
Urine, Physiological (in vivo)
No Effect:
Ascorbic acid
Citrates
Increase:
Ascorbic acid
Ethylene glycol
Methoxyflurane
Oxalate
Decrease:
Pyridoxine
Interfering Substance: Vanillymandelic Acid (VMA)
Urine, Physiological (in vivo)
No Effect:
Amphetamine
Angiotensin
Antibiotics
Barbiturates
Chlorothiazide
Clopamide
Dextroamphetamine
Digoxin
Ephedrine
Hydralazine
Isoproterenol
Mecamylamine
Meprobamate
Molindone
Neomycin
Oral contraceptives
Phenoxybenzamine
Phentolamine
Prochlorperazine
Season
Smoking
Thiothixene
Increase:
Ajmaline
Chlorpromazine
Creatinine clearance
Diurnal variation
Epinephrine
Glucagon
Guanethidine
Histamine
Insulin
Isoproterenol
Ketosis
Levarterenol
Levodopa
Lithium
Methyldopa
Muscular exercise
Nitroglycerin
Prochlorperazine
Rauwolfia
Reserpine
Starvation
Syrosingopine
Decrease:
Clonidine
Debrisoquin
Disulfiram
Ethanol
Guanethidine
Hydrazine derivatives
Imipramine
Isocarboxazid
Levodopa
MAO inhibitors
Methyldopa
Morphine
Nialamide
Phenothiazines
Radiographic agents
Reserpine
Uremia