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 |
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 |