Potential Assay Interference – Biochemistry Immunoassay Tests
The immunoassay methods used in the Biochemistry laboratory at Exeter Blood Sciences use a streptavidin-biotin system in their design. If patients are taking large doses of Biotin (Vitamin B7), there is potential for interference in immunoassays analysed within Biochemistry.
Biotin is a water soluble B vitamin, with a recommended daily intake of 50 μg/day (UK guidance). This should be easily attainable, as it is widely available in food, and the vitamin may also be produced by bacteria in the intestine.
The use of large doses of Biotin as a health supplement for a variety of issues has recently been promoted in the popular press. Its use may therefore pass unnoticed or be disregarded by patients when they are asked about over the counter medication/supplements which they may be taking. These supplements from health food shops, or obtained online, may contain Biotin concentrations of up to 10,000 μg per tablet. The tests highlighted in bold below may be somewhat affected by these supplements.
Clinical trials of supraphysiological doses of Biotin (up to 300,000 μg/day) are currently underway in patients who have been diagnosed with multiple sclerosis and other neurodegenerative disorders. Patients with metabolic disturbances may also be prescribed with high dose Biotin. All immunoassays analysed at Exeter Blood Sciences may be significantly affected at these concentrations.
Interference is not anticipated in patients not taking these high dose supplements.
If you have a test result which does not fit the clinical picture, you may wish to exclude possible Biotin interference as a cause, by asking the patient/parent/carer about any supplements they may have taken or check for a prescription. No commercial assay is available to measure the concentration of Biotin in blood samples.
Particular care should be taken in interpreting Troponin levels, where Negative interference has been reported.
Biotin is renally excreted, with a half-life of approximately 2 hours in low doses. The manufacturers of the methods used in the Biochemistry laboratory advise that samples should not be taken from patients receiving therapy with high biotin doses (>5,000 μg/day) until at least 8 hours after the last biotin administration.
Suggested biotin withdrawal times based on pharmacokinetic studies are as follows:
Less than 1000 μg/day (1 mg/day): 2 hours
1000-10000 μg/day (1-10 mg/day): 8 hours
10000 μg/day or above (10 mg/day or above): 72 hours
From: Grimsey et al, 2017, Population pharmacokinetics of exogenous biotin and the relationship between biotin serum levels and in vitro immunoassay interference. Int J Pharmacokinet 2 (4) 247-256.
However, this information relies on a number of factors, including the renal status of the patient. Biotin levels in patients with CKD/AKI may be higher as a result.
Reference:
Jenkins Colon, P, Greene, D.N. Biotin Interference in Clinical Immunoassays. J Appl Lab Med (2018) DOI: 10.1373/jalm.2017.024257
This table indicates the levels of Biotin above which the assay may be affected.
The concentration of Biotin in the blood of a person not taking supplements is <1 nmol/L
| Assay | Biotin (nmol/L) | Biotin Effect | Assay type |
| AFP | ≤ 4912 | Negative | Sandwich |
| AMH Plus | ≤ 4912 | Negative | Sandwich |
| Free Beta HCG | ≤ 4912 | Negative | Sandwich |
| FSH | ≤ 4912 | Negative | Sandwich |
| NT-pro BNP | ≤ 14326 | Negative | Sandwich |
| PAPP-A | ≤ 4912 | Negative | Sandwich |
| Thyroglobulin | ≤ 4912 | Negative | Sandwich |
| Total PSA | ≤ 4912 | Negative | Sandwich |
| Troponin-T hs | ≤ 4920 | Negative | Sandwich |
| TSH | ≤ 4912 | Negative | Sandwich |
| Anti-TG | ≤ 4912 | Positive | Competition |
| FT3 | ≤ 4912 | Positive | Competition |
| FT4 | ≤ 4912 | Positive | Competition |
| Testosterone | ≤ 9000 | Positive | Competition |
| Vitamin D | ≤ 2456 | Positive | Competition |
