PTH after total thyroidectomy,a predictive factor for long-term hypoparathyroidism?

Total thyroidectomy is the operation of choice for many patients with thyroid
carcinoma, and sometimes with Graves* disease or multinodular goitre.
Postoperative hypoparathyroidism, following total thyroidectomy is a common
iatrogenic complication leading, among other factors, to hypocalcaemia. Up to
55-60% of the patients develop serum calcium levels below 2.00 mmol/L on the
first day after surgery. Therefore it is routine practice to monitor patients
clinically for signs and symptoms of hypocalcaemia as well as perform regular
measurements of serum calcium levels. Recent studies (2,3) have shown that a
serum parathyroid hormone (PTH) concentration obtained 4-24 hours
postoperatively is the most significant factor to predict postoperative
hypocalcaemia. In most patients with post-thyroidectomy hypocalcaemia,
parathyroid function (if any glands are left) restores within several weeks.
However, up to 5-10% of the patients may develop persistent hypoparathyroidism
and require lifelong calcium supplementation. In a study by Sitges-Serra et
al.1 evaluating 442 patients after total thyroidectomy, 222 patients had
postoperative hypocalcaemia. Of them, 40% (80/222 patients) still had
hypocalcaemia one month after surgery. PTH levels were also measured one month
after surgery: 90% (40/44 patients) of the patients with low PTH levels
recovered to normal parathyroid function within one year compared with 62% of
the patients with undetectable parathyroid levels (21/34 patients). Logistic
regression analysis identified undetectable PTH levels one month after surgery
to predict permanent failure of parathyroid function. However, PTH levels
directly after surgery were not measured. We aim to identify a predictive
factor for persistent hypoparathyroidism after a total (or completion)
thyroidectomy that can be obtained directly after surgery. This would not only
be valuable for planning outpatient appointments, but would also provide more
certainty for the patient. In addition calcium supplementation can become more
patient tailored at the outpatient department, aiming to reduce the negative
consequences of hypocalcaemia, unnecessary visits and laboratory
investigations. Therefore the aim of our study is to investigate whether PTH
levels measured between 4-242,3 hours after surgery will identify patients who
need long-term calcium supplementation.

The aim of our study is to investigate whether PTH levels measured between 4-24
hours after surgery can accurately identify patients with permanent
hypoparathyroidism after thyroid surgery who need long-term calcium
supplementation.

This extra protocol applies to all patients who have given informed consent.
1. Prior to surgery (outpatient department), (Day -1)
a. Check informed consent and contact with study coordinator
b. Lab (t=0): Routine laboratory screening, including: calcium/
phosphate/albumin/vitamin D including: PTH for the study
2. Day of surgery (Day = 0)
a. Lab (t=1 / 18:00): Routine laboratory screening (calcium, phosphate,
albumin, vitamin D), including: PTH for the study
3. Day after surgery (Day = +1)
a. Lab (t=2 / 08:00): Routine laboratory screening (calcium, phosphate,
albumin), including: PTH for the study
4. 1-2 weeks after surgery
a. Lab (t=3): Routine laboratory screening (calcium, phosphate, albumin),
including: PTH for the study
5. 1 year after surgery
a. Lab (t=4): Routine laboratory screening (calcium, phosphate, albumin),
including: PTH for the study
Interpretation of laboratory findings and calcium supplementation are based on
the existing protocol (Attachment 1) which is not changed for the purpose of
the study.

not applicable.