Letter to the editor

To the Editor: We read with interest the article “Same-day Discharge after Total Thyroidectomy: The Value of 6-Hour Serum Parathyroid Hormone and Calcium Levels” by Richard J. Payne et al in the January 2005 issue of Head & Neck regarding a “Post–total thyroidectomy blood test that can accurately identify the patients who will have hypocalcemia develop.”1 We are sure that, like ours, most of the units practicing total thyroidectomy (TT) are in search of a blood test that can identify the patients who are likely to become hypocalcemic. The 6-hour serum parathyroid hormone (PTH) and calcium levels test in this study are 100% specific but have only 70% sensitivity. Because post-thyroidectomy hypocalcemia is of multifactorial origin, a single blood test cannot be an accurate predictor. In our practice, most patients become hypocalcemic after 24 to 48 hours. We think that risk factors for hypocalcemia in various previous studies, such as preoperative serum calcium,2 vitamin D levels, elevated free thyroxine levels,3 bilateral thyroidectomy,3 parathyroid autotransplantation or in situ function,3 and serum magnesium levels, should be considered in the study before reaching a conclusion. We have found that most of the Indian population is vitamin D deficient despite adequate sun exposure. If the vitamin D levels were available for the patients, the authors' view of vitamin D deficiency contributing to hypocalcemia would have been corroborated. The cost-effectiveness of the test is also an important issue. In our hospital, TT routinely costs approximately Rs 20,000 (US $500), and a single test of immunoassay for parathyroid hormone (iPTH) costs Rs 1200 (US $27) by immunoradiometric assay (IRMA) estimation. The cost of the chemiluminescence method is not known, because many hospitals do not have the facilities. In India and many other third-world countries, many hospitals do not have the facilities for PTH estimation, and commercial laboratories that have networks all over the country do it, but the results are available only after at least 72 hours. Only a few referral centers and hospitals have the facilities for chemiluminescence assay; otherwise, estimation is done by IRMA assay, which requires overnight incubation. We believe that this test has applicability only in select hospitals in our country that have the facilities for rapid PTH assay. This subject will remain an interesting area for future prospective studies. Reply: We thank Drs. Anand Kumar Mishra and Amit Agarwal for their comments. The goal of our study1 was to ensure that post-thyroidectomy patients meeting the critical 6-hour serum parathyroid hormone (PTH) level (28 ng/L) and corrected serum calcium level (2.14 mmol/L) were not at risk of developing hypocalcemia. The study has resulted in earlier discharges from the hospital, fewer blood tests, and significant cost savings at our institution.2 Before the study, our group had made the decision to set the serum PTH and corrected calcium criteria at a level that would achieve a maximal specificity at the expense of sensitivity. The reasoning was to ensure that post-thyroidectomy patients at risk for hypocalcemia would not be discharged from the hospital. We agree with the comment that a single blood test cannot accurately determine the risk of hypocalcemia developing in post-thyroidectomy patients. It was this principle that led us to deviate from previous trials that monitored for hypocalcemia focusing solely on serum calcium levels alone.3, 4 Although our system does not provide information as to the etiology of the hypocalcemia, it does provide the practitioner with a tool to identify patients who are not at risk for developing hypocalcemia. Moreover, some patients in this study failed to meet the criteria at 6, 12, and 20 hours post-thyroidectomy and had hypocalcemia develop as late as 48 hours. In terms of the cost analysis and the method used in North America, automated immunoassays are in fact less expensive than semiautomated or manual assays, because less time by the technologist is required. Several automated instruments on the market are capable of doing PTH in a rapid manner, and most of these are used for routine immunoassays in the laboratory. It does not require additional investment in equipment or staff in most major centers. Each hospital must determine itself whether there are cost savings accrued through the early discharge of post-thyroidectomy patients. Richard J. Payne, MD, FRCS(C) Michael P. Hier, MD, FRCS(C) Michael Tamilia, MD, FRCP(C) Elizabeth Mac Namara, MD, FRCP(C) Jonathan Young, MD Martin J. Black, MDCM, FRCS(C) Jewish General Hospital, McGill University, Montreal, Canada

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