American Association for Clinical Chemistry
Better health through laboratory medicine
NACB - Scientific Shorts
NACB - Scientific Shorts (formerly NACB Blog)
By William Winter, MD
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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).

 

 

 

 

 

 

 

 

 

 

 

 

 

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Posted by
On 2/10/2012

We have 24/7 on call lab personnel for liver transplants, with one of the duties to courier samples from the OR to perfrom TEG testing in the blood bank. The OR staff is already certified to perform other non-waived testing, but the lab personnel continue to handle the TEG.

Posted by
On 2/8/2012

Our institution considered TEG for years, but implementation of a very active strategic blood management program a couple of years ago made this an imperative for the institution. In the past year, new surgeons (esp. intraabdominal tx) have come on board looking for this technique to help monitor parameters as Dr. Stickle described. Collaborating with anesthesiologists in OR, our blood utilization committee, the surgeons and our department, we decided to implement ROTEM which is a slightly different analytical technique from TEG, but provides much of the same clinical information. In conjunction with recent FDA approvals of a couple of the methods, we're in the final stages of validations for instruments in the OR Lab and Core Lab. Our staff find it very interesting to use. Kind of a 'cool' concept for a clinical biochemist like me. But its use absolutely requires the buy in and support from key clinicians - especially in the anesthesiology and surgical groups. Steve Kahn, Ph.D. Loyola University Health System Maywood, IL, USA

Posted by
On 2/8/2012

TEGs are being aggressively marketed as a means to reduce blood product consumption. It was implemented by cardiac anesthesia at our hospital without laboratory approval. It is very difficult for laboratory POCT coordinators to oversee POCT in the ORs. I am very greatful to the CAP inspection team that visited us and investigated TEG operations in the OR. They found several major deficiencies, which brought the issue to the attention of senior hospital administration. It is being done by one anesthesiolgist and a few cardiac perfusionists on a limited basis. I'm not convinced that there is a favorable cost/benefit ratio for this test. I would like to see it recategorized as high complexity. I do not think it is appropriate for POCT by non-laboratory personnel.

Posted by
On 2/8/2012

Thanks Doug, I agree, this will be unfamiliar territory for the OR staff. Athough many cardiac ORs have experience with performing ABGs and ACTs at the POC, in contrast, ROTEM requires reagents to be placed in a certain order, pipetting and reconstitution of reagents. My 2 cents: This test should not be performed POC in the ORs by OR staff. They are too distracted with other duties to be laboratorians as well. How many users will be trained, how will they remain competent? From a patient care and risk perspective, I advocate for the more expensive option of laboratory performed testing and output in the OR. (This can be complicated too depending on your LIS, distance from the OR, and how the data are transmitted eg. meeting HIPPA standards). Thanks for your post. Corinne Fantz

Posted by
On 2/7/2012

TEG is a moderate-complexed instrument. The QC requirements are strict and anesthesiolgists found it difficult to comply with the every 8 hours QC requirement at the OR setting. In addition, the group finds it difficult to spend adequate time to learn patient testing and interpretations. The implementation would go well if the anesthesiolgists are dedicated to the training and have enough time to practice QC/patient testing with the instrument. Some complained about the long duration to wait for the results. Laboratoians can do a better job to run TEG on patients.

About the Author
William Winter, MD
William Winter, MD 
 

Malone, B: Rethinking Ionized Calcium Test Utilization. Clinical Lab Strategies, May 2009