Drugs and other substances that can interfere with Biochemistry tests

INTERFERING SUBSTANCES

Interference by exogenous substances, including some drugs, can affect results of 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 naturally present in the diet. The required daily intake of biotin is quite small (30-70 micrograms), and most diets will contain sufficient amounts. Multivitamin supplements also often contain biotin in these small amounts.

Higher dose biotin supplements (5-10mg, sometimes higher) are available over-the-counter, marketed for hair, skin and nail health, and also sometimes prescribed as a treatment for multiple sclerosis or some inherited metabolic disorders. These can potentially interfere with some biochemistry tests called “immunoassays”.

Biotin interference can cause falsely high or low results depending on the design of the immunoassays. Competitive assays may give falsely high results, and sandwich assays may give falsely low results.

Rotherham and Barnsley Hospitals use the Siemens Atellica platform for their blood tests. These assays are generally quite resistant to biotin interferences, even at high biotin concentrations. Siemens have however identified some of their assays which may be affected in patients taking high dose biotin supplements (at least 5-10mg/d):

Assay	Assay design	Possible result interference
Serum folate	Competitive immunoassay	Falsely increased
Brain natriuretic peptide (BNP)	Sandwich immunoassay	Falsely decreased
Pro N-terminal brain natriuretic peptide (Pro-NT BNP)	Sandwich immunoassay	Falsely decreased
Erythropoietin (EPO)	Sandwich immunoassay	Falsely decreased
Sex hormone binding globulin (SHBG)	Sandwich immunoassay	Falsely decreased
Testosterone	Competitive immunoassay	Falsely increased

The half-life of biotin varies significantly depending on the dose taken and the dosing schedule, and other factors such as the patient’s renal function. If you are planning a non-urgent test for a patient taking biotin therapy (at a dose of 5mg or higher) which can be safely stopped, the biotin should be stopped for 1 week before testing. If the patient cannot safely stop taking the biotin, or testing is required within 1 week of their last dose, please contact the Duty Biochemist via Switchboard to discuss.

References:

Biotin interference in certain immunoassays (Atellica IM Analyzer), Siemens Healthineers Customer Bulletin, September 2019.
Avery G. Biotin interference in immunoassay: a review for the laboratory scientist. Annals of Clinical Biochemistry. 2019;56(4):424-430. doi:10.1177/0004563219842231

OTHER INTERFERENCES

Aside from Biotin, there are a number of substances (including some drugs) that can have an effect on assay 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
CA125	Fluorescein	Falsely high/ falsely low- do not test if patient has been administered fluorescein within the last 72hrs	SA IFU Rev 01	June 2023
Cortisol	Prednisolone/ prednisone	Falsely high	SA IFU Rev 03	June 2023
Cortisol	Metyrapone	Falsely high	SA IFU Rev 03	June 2023
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
Digoxin	Digibind ®	Affects test- discuss with Duty Biochemist	SA IFU Rev 05	June 2023
Erythropoietin	Acetaminophen (paracetamol)	Falsely low	SA IFU Rev 05	June 2023
HDL Cholesterol	N-acetylcysteine	Falsely low	SA IFU Rev 04	June 2023
HDL Cholesterol	Metamizole (sulpyrine)	Falsely low	SA IFU Rev 04	June 2023
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
Triglycerides	Metamizole (sulpyrine)	Falsely low	SA IFU Rev 04	June 2023
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
Uric acid	Metamizole (sulpyrine)	Falsely low	SA IFU Rev 03	June 2023
Vitamin D	Fluorescein	Falsely high- do not test if patient has been administered fluorescein within the last 72hrs	SA IFU Rev 04	June 2023