Severe hypocalcemia without symptoms - Another lab error?

Case: A 58-year-old man underwent MRI total body imaging. Later that day, a chemistry profile was ordered. The total calcium was measured at 4 mg/dL (reference interval: 8.5-10.5 mg/dL) and the albumin was 4 g/dL (reference interval: 3.5-5.0 g/dL). The patient was examined and lacked any clinical evidence of hypocalcemia. One week prior to the MRI, the total calcium was normal. What is the explanation for the hypocalcemia?

Answer: Certain gadolinium contrast agents falsely lower the measurement of total calcium when calcium is measured using colorimetric assays. Gadodiamide (Omniscan) and gadoversetamide (OptiMARK) have been reported to cause such "pseudohypocalcemia." [1] On the other hand, gadoteridol (ProHance) and gadopentetate dimeglumine (Magnevist) have not been reported to effect total calcium measured colorimetrically. In a recent paper from Germany, gadobutrol (Gadovist) and gadoxetate disodium (Primovist/Eovist) were reported to not affect calcium measurements. [2]

If your hospital uses a gadolinium formulation that does interfere, it is recommended that calcium be measured before the procedure or more than 4 hours post-MRI when the patient's GFR is =>90 mL/min/1.73 M2 or more than 50 hours post-MRI when the GFR is reduced to ~20 mL/min/1.73 M2.

1. Emerson J, Kost G. Spurious hypocalcemia after Omniscan- or OptiMARK-enhanced magnetic resonance imaging: an algorithm for minimizing a false-positive laboratory value. Arch Pathol Lab Med. 2004 Oct;128(10):1151-6.
2. Löwe A, Breuer J, Palkowitsch P. Evaluation of the effect of two gadolinium-containing contrast-enhancing agents, gadobutrol and gadoxetate disodium, on colorimetric calcium determinations in serum and plasma. Invest Radiol. 2011 Jun;46(6):366-9.

Final question: what disease can develop in patients with renal failure who receive gadolinium for scans? (answer next week).

Gadolinium-associated nephrogenic systemic fibrosis. [1]

1. Schlaudecker JD, Bernheisel CR. Gadolinium-associated nephrogenic systemic fibrosis. Am Fam Physician. 2009 Oct 1;80(7):711-4.