Validation of thyroid/parotid ratio (TPR) in the diagnosis of hyperthyroidism A Multi-centre study

Full text: Thyroid to Parotid Ratio (TPR) as a simple and cost effective diagnostic test in the evaluation of thyroid disorders was first reported by us in 1997P. Since then several authors have used this procedure for the diagnosis and differential diagnosis of high uptake thyroid conditions. The purpose of this multi centric study was to validate this simple technique and establish its clinical usefulness in a large number of patients at different environmental conditions and ethnic populations. Material and method: Prospective study which included following patients: 43 consecutive hyperthyroid patients (26 male and 17 female) from eastern Malaysia (high dietary iodine) sent for radio iodine therapy between May 2005 and Dec. 2006; 578 patients (212 male and 366 females) from northern part of India (endemic goiter region) diagnosed to have hyperthyroid conditions between Jan. 1996 and Dec.2002 and 19 consecutive patients (8 males and 11 females) from south India (non- endemic goiter region ) clinically and bio chemically hyperthyroid, referred between June 2005 and Dec. 2006. All patients were subjected to a standard Tc99m thyroid scan. Thyroid to Parotid Ratio (TPR) was calculated after drawing ROIs over the thyroid and parotid glands in anterior projection. Blood samples were taken on the same day for TB3B, TB4B and TSH (RIA) The TPR values were compared with the biochemical parameters. Results: The individual comparison of clinical and biochemical parameters with TPR in hyperthyroid patients showed concordance [TPR > 2.5 (normal ± 2 SD)] in over 90 % in all the three centers (Kelantan 91 %, Lucknow 93.7 % and Madurai 96.5 %). Conclusions: Calculation of TPR is extremely simple without the requirement of syringe counts or adhering to any time frame. It is highly sensitive and specific in the diagnosis of hyperthyroidism. The morphological information obtained from the scan and the objective TPR value for functional status is sufficient to start definitive therapy on the same day in most cases without waiting for biochemical test values. In a retro prospective review it was found that out of the total of 311 patients referred to Nuclear Medicine dept at Lucknow between 1998 and 2001, 180 patients could be diagnosed to have hyperthyroidism and could be given a definitive therapy (mostly radio iodine) on the same day using this approach. This saved time, cost and inconvenience to the patients who were mostly from poor socio-economic background and came from far off places. (author)