TS is usually reported along with the serum iron (SI) and total iron binding capacity (TIBC). TS indicates the percent of iron binding sites on transferrin that are carrying iron.
TS is derived from a calculation using the formula:
TS =(SI/TIBC) x 100
TS results are reported as percentages. Typical reference intervals for TS are 20% to 55% for males and 15% to 50% for females.
TS is currently considered to be a good test for screening persons for HH due to its sensitivity and specificity for iron overload. It may be elevated prior to significant deposition of tissue iron. TS levels increase as additional iron is accumulated.
A drawback to using the TS is that it is dependent on performing both the SI and TIBC. The unsaturated iron-binding capacity UIBC may be a lower cost alternative.
The optimal TS criterion for detecting HH is controversial. Using a TS of >60% for males and >50% for females has been found highly accurate in detecting abnormal iron metabolism in persons with HH. Others studies suggest using lower TS levels, e.g. 45%, as a criterion indicating further testing is warranted. Current guidelines from the American College of Physicians include a TS cutoff level of >55% for identifying iron overload. (14) A TS cutoff level of >45% is recommended by the American Association for the Study of Liver Disease. (15)
Patients with initially increased TS should be followed by performing a second TS from a fasting morning specimen. The patient should also be advised not to take vitamins supplemented with iron or oral contraceptives for several days prior to the repeated test. TS levels may be affected by diurnal variation, dietary factors, and co-existing disease states such as inflammation and hepatitis. Patients with HH may have falsely normal TS if chronic blood loss or inflammatory disease is present.