Urinary ferritin as a non-invasive means of assessing iron status in young children.

Background Iron deficiency (ID) is the most common nutritional deficiency affecting young children. Serum ferritin is the preferred biomarker for measuring iron status as it reflects iron stores; however, blood collection can be distressing for young children and can be logistically difficult. A Non-invasive means to measure iron status would be attractive to either diagnose or screen for ID in young children. Objective 1) To determine the correlation between urinary and serum ferritin in young children; 2) To determine if correcting urinary ferritin for creatinine and specific gravity improves the correlation; and 3) To determine a urine ferritin cut point to predict ID. Methods Validation study using paired serum and urine collected from 3-year-old children (n=142) participating in a longitudinal birth cohort study; the ORIGINS project in Perth, Western Australia. We calculated the sensitivity, specificity, positive, and negative predictive value of urinary ferritin in identifying those with ID at the clinical cut point used by the World Health Organization (serum ferritin <12 ng/mL). Results Urine ferritin, corrected for creatinine, correlated moderately with serum ferritin r=0.53 (0.40-0.64) and performed well in predicting those with ID (area under the curve 0.85, 95% CI 0.75-0.94). Urine ferritin < 2.28 ng/mg creatinine was sensitive (86%) and specific (77%) in predicting ID and had a high negative predictive value of 97%; however, the positive predictive value was low (40%) due to the low prevalence of ID in the sample (16%). Conclusions Urine ferritin showed good diagnostic performance for ID. The non-invasive biomarker maybe a useful screening tool to exclude ID in healthy young children; however, further research is needed in other populations.