Iron, Random, Urine
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Iron is an essential element, serving as an enzyme cofactor and facilitating oxygen transport. Iron is cleared primarily by biliary excretion via the feces and secondarily by renal clearance, which is a relatively minor route of clearance. Excessive accumulation of iron in iron-overload diseases leads to higher than normal urine concentration of iron, known as hemosiderinuria.
Diagnosis of hemochromatosis, hemolytic anemia, paroxysmal nocturnal hemoglobinemia, and impaired biliary clearance (limited value).
Note: The preferred specimen for assessing urinary iron excretion is a 24-hour urine specimen.
Normal excretion of iron occurs at the rate of approximately 100 mcg/L to 300 mcg/L. In the event that dietary iron is below minimum daily requirements (<2 mg/day in females, <1 mg/day in males), urinary excretion will be less than normal.
Urinary iron is greater than normal in iron overload. It is not uncommon to observe iron excretion >20,000 mcg/L in a patient with clinically evident hemochromatosis. Daily urine output of iron ranging from 500 mcg to 5,000 mcg suggests active hemolytic anemia, early-stage hemochromatosis, or impaired biliary clearance.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Because iron elimination undergoes extreme diurnal variation (serum levels 10 times higher in a.m. than p.m.), results from random urine specimens can be very misleading and are of limited value; 24-hour specimens are preferred.
High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium- or iodine-containing contrast media has been administered, a specimen should not be collected for 96 hours.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
0-15 years: not established
> or =16 years: 100-300 mcg/L
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Gurzau ES, Neagu C, Gurzau AE: Essential metals case study on iron. Ecotoxicol Environ Saf 2003;56:190-200
2. Ludwig J, Batts KP, Moyer TP, Poterucha JJ: Advances in liver biopsy diagnosis. Mayo Clin Proc 1994;69:677-678