Artifactual Hypocalcemia from Gadodiamide Interference

Gadolinium-based contrast agents (GBCAs), such as gadodiamide, are known to interfere with colorimetric calcium assays, leading to spurious hypocalcemia. This case highlights the importance of recognizing such interference to avoid unnecessary clinical interventions.

A 51-year-old woman presented with a critically low serum calcium level (1.44 mmol/L) detected during routine testing. Repeat testing 4 hours later showed normalization (2.12 mmol/L). Investigations ruled out preanalytical and analytical errors.

The discrepancy was attributed to gadodiamide administration for MRI 24 hours prior to blood sampling. The agent's interaction with the methylthymol blue (MXB) reagent artificially lowered calcium measurements. No interventions were required.

Laboratory-clinical collaboration is essential to identify GBCA-induced artifactual hypocalcemia. Education on blood draw timing and alternative assays (e.g., ion-selective electrodes) is critical.