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Drugs and other substances that can interfere with Biochemistry tests

INTERFERING SUBSTANCES

Interference by exogenous substances, including drugs, can affect results biochemistry tests. Below we have listed some examples of potential interferences known to the Biochemistry lab.

Should any result not fit with the clinical context of the patient, you can discuss this with the Duty Biochemist (in office hours), on Consultant On-Call out of working hours, available via Switchboard.

BIOTIN

Biotin (vitamin B7) is an essential nutrient present in the diet. A normal diet will provide sufficient of this micronutrient and many over the counter multivitamins contain biotin in small amounts. However, higher dose supplements are available over the counter and the vitamin can be prescribed in treatment for some disorders (eg multiple sclerosis). Biotin is an important component in some of our assays and very high (supra-physiological) doses can potentially cause interference in these analyses. The effect is dependent upon the format of the assay, resulting in falsely high or falsely low results. This can potentially affect many of our immunoassay tests which measure things like hormones, haematinics, tumour markers and troponin.

OTHER INTERFERENCES

Aside from biotin, there are a number of drugs that can have an effect on results. See the table below for a list of substances known to interfere with our assays. Please note, this list is not exhaustive and, as mentioned above, please contact the lab if the results do not fit the clinical picture

 

Test

Interfering substance

Effect

Reference

Date of review

ALT

Sulfasalazine

Falsely low

SA IFU Rev 05

June 2023

Cortisol

Prednisolone/ prednisone

Falsely high

SA IFU Rev 03

June 2023

Metyrapone

Falsely high

Creatinine

N-acetylcysteine

Falsely low

SA IFU Rev 06

June 2023

Acetaminophen (paracetamol) (in overdose)

Falsely low

Dobesilate

Falsely low

Metamizole (sulpyrine)

Falsely low

Phenindione

Falsely low

Cefoxitin

Falsely low

Dipyrone

Falsely low

Dobutamine

Falsely low

Dopamine

Falsely low

Ethylglycine

Falsely high

Digoxin

DigiFab®

Affects test- discuss with Duty Biochemist

SA IFU Rev 05

June 2023

Digibind ®

Erythropoietin

Acetaminophen (paracetamol)

Falsely low

SA IFU Rev 05

June 2023

HDL Cholesterol

N-acetylcysteine

Falsely low

SA IFU Rev 04

June 2023

Metamizole (sulpyrine)

Falsely low

Lactate

N-acetylcysteine

Falsely low

SA IFU Rev 04

June 2023

Oestradiol

Fulvestrant

Falsely high

SA IFU Rev 06

June 2023

Paracetamol (acetamenophen)

N-acetylcysteine

Falsely low

SA IFU Rev 04

June 2023

Metamizole (sulpyrine)

Falsely high

Rifampicin

Falsely high

Progesterone

Dehydroepiandrosterone (DHEA)

Falsely high

SA IFU Rev 05

June 2023

Salicylate

Sulfasalazine

Falsely high

SA IFU Rev 04

June 2023

Sulfapyridine

Falsely low

Temozolamide

Falsely high

Testosterone

Nandolone decanoate

Falsely high

SA IFU Rev 07

June 2023

11B-hydroxytestosterone

Falsely high

11-ketotestosterone

Falsely high

Total Protein

Dextran

Falsely high

SA IFU Rev 03

June 2023

Triglycerides

N-acetylcysteine

Falsely low

SA IFU Rev 04

June 2023

Metamizole (sulpyrine)

Falsely low

TSH

Fluorescein

Falsely low- do not test if patient has been administered fluorescein within the last 72hrs

SA IFU Rev 05

June 2023

Uric acid

N-acetylcysteine

Falsely low

SA IFU Rev 03

June 2023

Metamizole (sulpyrine)

Falsely low

Vitamin D Fluorescein Falsely high- do not test if patient has been administered fluorescein within the last 72hrs SA IFU Rev 04

June 2023