---
title: "Blood Test Interference & eGFR Diagnostic Adjuster | Nutrition Research Labs"
source_url: "https://nutritionresearchlabs.com/tools/blood-test-interference"
canonical_url: "https://nutritionresearchlabs.com/tools/blood-test-interference"
retrieved_by: "AnswerRail Edge Engine v1.1.0-parity-v20 (https://answerrail.com)"
provenance: "Compiled for deterministic AI retrieval by AnswerRail Edge (RFC 9110 / RFC 9421)"
description: "Clinical supplement lab test interference checker. Detect biotin immunoassay false positives (Troponin, TSH), creatine-induced pseudo-creatinine elevations, and calculate cystatin-C corrected eGFR."
rfc_compliance: "RFC 9110 / RFC 9309 / RFC 9421"
version: "1.1.0"
release_version: "v1.1.0-parity-v20"
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---

> **Canonical Source:** [https://nutritionresearchlabs.com/tools/blood-test-interference](https://nutritionresearchlabs.com/tools/blood-test-interference)
>
> *Clinical supplement lab test interference checker. Detect biotin immunoassay false positives (Troponin, TSH), creatine-induced pseudo-creatinine elevations, and calculate cystatin-C corrected eGFR.*

## FDA-Documented Dietary Supplement Diagnostic Interferences

| Supplement / Compound | Affected Lab Assay | Clinical Artifact / Direction | Recommended Washout Window |
| :--- | :--- | :--- | :--- |
| Biotin (Vitamin B7 >5mg) | Cardiac Troponin I/T, TSH, Free T4 | Falsely low Troponin (missed MI), falsely high T4 | 48 – 72 hours prior to draw |
| Creatine Monohydrate | Serum Creatinine & CKD-EPI eGFR | Falsely elevated Creatinine / artificially suppressed eGFR | Use Cystatin-C eGFR (unaffected by muscle) |
| High-Dose Ascorbic Acid (Vit C) | Point-of-Care Blood Glucose Meters | Electrochemical redox interference (falsely high glucose) | 24 hours before capillary test |
| Ashwagandha (Withanolides) | Digoxin Immunoassays | Cross-reactivity causing pseudo-toxic Digoxin levels | 7 days before therapeutic drug monitoring |

## Renal Filtration: Creatinine vs Cystatin-C Correction

Creatine supplementation increases the spontaneous conversion rate to creatinine by 15–30%, falsely dropping calculated eGFR into Stage 2/3 Chronic Kidney Disease ranges without any actual renal impairment.

The 2021 CKD-EPI Cystatin-C equation eliminates muscle-mass and supplement bias to establish ground-truth glomerular filtration.

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