Blood Iron Test Predicts Fatal Outcomes

The transferrin saturation (TSAT) ratio is a commonly used indicator of iron deficiency and iron overload in clinical practice, but precise relationships with total and cardiovascular mortality are equivocal.

The test is a measure of the amount of available iron in the bloodstream with low levels generally reflecting a state of iron deficiency and high levels suggesting a relative excess which can be detrimental to health.

Scientists at the University of Limerick (Ireland) studied 15,823 participants, 20 years of age or older, who had a valid serum creatinine value. Serum creatinine values were used to determine the estimated glomerular filtration rate (eGFR) in mL/min/1.73 m² for all participants. Blood samples were obtained from nonfasting persons and frozen serum sent for analysis.

Serum iron and total iron binding capacity were measured colorimetrically (Alpkem RFA analyzer; Clackamas, OR, USA), and serum ferritin was measured with the Quantimmune IRMA kit (Bio-Rad Laboratories; Hercules, CA, USA). Hemoglobin was measured using a Coulter S-Plus Jr electronic counter (Coulter Electronics; Hialeah, FL, USA). Serum creatinine concentrations were measured by the modified kinetic Jaffe reaction using a Hitachi 737 analyzer (Boehringer Mannheim Corp.; Indianapolis, IN, USA).

The study found that subjects with extremely low transferrin saturation levels of less that 17.5% were at a 45% higher risk of death. On the other hand, the risk of death was also significantly higher for subjects with very high levels of transferrin saturation above 31.3 %. The mean values for TSAT were 26.3 %; hemoglobin 14.2 g/dL and serum ferritin level 129 ng/mL. The association of TSAT with mortality differed by race and sex. Among whites and blacks, low and high TSAT levels were associated with higher mortality risk while no association was manifest in Mexican-Americans. For men, the impact on mortality was demonstrated only in older males, while for women the j-shaped mortality association was confined to younger females. High levels usually occur in states of iron overload like hemochromatosis, multiple blood transfusions and cirrhosis.

Austin G. Stack MD MSc, a professor and senior author of the study said, “Our analysis suggests that the optimal transferrin saturation range for patient survival should be between 23% to 40% and that careful clinical assessment is warranted for patients with low and high levels in order to identify states of iron deficiency or iron excess. Our study demonstrates that transferrin saturation ratio is a useful prognostic tool in assessing a patient's health and while we support the correction of low transferrin saturation levels in the general population, we would also advise caution against excessive iron loading to levels beyond 40%.” The study was published on March 5, 2014, in the Quarterly Journal of Medicine.

Related Links:
University of Limerick
Alpkem
Bio-Rad