Thyroid hormone binding protein abnormalities in patients referred for thyroid disorders.

BACKGROUND & OBJECTIVES: Thyroid hormone binding protein (THBP) abnormalities are the major cause of discordance in commonly performed total thyroxine (T4) and thyrotropin (TSH) estimations, though these do not interfere with thyroid hormone action. Determination of such abnormalities in patients showing discordant thyroid function tests (TFTs) is diagnostically important as it eliminates equivocal assessment of thyroid function and treatment especially where proper methodology for free T4 (FT4) estimation is not available. This study was undertaken to analyse the THBP abnormalities in the population attending thyroid clinic. Family members of affected patients were also screened to study the inheritance of quantitative TBG abnormalities. METHODS: Blood samples of 15000 consecutive patients over a period of 4 years (1994-1997) were tested for thyroid function. THBP abnormalities were studied using polyacrylamide gel electrophoresis autoradiography. Serum thyroxine binding globulin (TBG), free and total T4, total tri-iodothyronine (TT3) were assayed by radioimmunoassay methods. RESULTS: In our screening of 15,000 thyroid patients over a four year period, we found the presence of complete and partial TBG deficiency and TBG excess to be 1:2,500, 1:200 and 1:15,000 respectively. Our study on the families of three affected patients revealed X-chromosome linked inheritance pattern of TBG deficiency in two families and TBG excess in one family. INTERPRETATION & CONCLUSION: Our study suggests that it would be beneficial to rule out THBP abnormalities before interpreting results of TFTs, particularly when there is large discrepancy between T4 and TSH levels. In case of inherited THBP abnormalities, the family members of the affected individual should also be screened to avoid misdiagnosis and erroneous treatment in case they develop thyroid dysfunction in future.

Comparative evaluation of immunochemical methods for estimation of albumin in microalbuminuria.

Three immuno assays namely radioimmunoassay (RIA), radial immunodiffusion (RID) and rocket immunoelectrophoresis (RIE) were compared for their performance and utility. The accuracy limits of the methods were compared and also between methods using RIA as the reference. Urine samples, from known diabetic patients with albumin concentration ranging from 2.5 mg/l to 120 mg/l were analysed by the three methods. The mean differences were only 0.91 mg/dl and 0.5 mg/dl respectively for RID vs RIA and rocket vs RIA which is not statistically significant. Excellent correlation was seen between RIA and RIE (r = 0.98) and also between RIA and RID (r = 0.97). Compared to RID, RIE required less time and was more precise. RIA is suited for assaying large sample loads yet not suited for laboratories receiving samples occasionally. For a small pathological laboratory with limited facility rocket electrophoresis may be the most suitable method taking into consideration accuracy, time and cost.