Cascade testing of primary care blood samples with hyperferritinaemia identifies subjects with iron overload and porphyria cutanea tarda.

INTRODUCTION

Serum ferritin is routinely used as a first line test for iron status. Testing subjects with low pre-test probability often results in unexpected abnormal results. Raised ferritin is typically found in subjects with iron overload, liver disease, malignancy or inflammation. We sought to determine whether primary care patients with high ferritin had either porphyria cutanea tarda (PCT) or hereditary haemochromatosis (HH).

METHODS

Redundant serum samples were collected from consecutive specimens with high ferritin (>500 µg/L) which had been received from primary care sources. Samples were analysed for serum iron and iron-binding capacity and for porphyrins by fluorescence scanning and HPLC.

RESULTS

There were 240 samples (91 females, 149 males) which represented 2.7% of total over the collection period. Serum iron was 17.3 (18.9) µmol/L (median (IQR)), TIBC 47.3 (14.2) µmol/L and transferrin saturation 35.7 (41.1) %. There were 87/240 (36%) with transferrin saturation >45% (57 males, 30 females). Of the samples 19/236 (8%) were positive for porphyrins by spectrofluorimetry and 14/15 (4 insufficient sample) had total porphyrins >11.2 nmol/L (40(63) median (IQR)) with 3/15 (1.25%) having a typical pattern for PCT.

DISCUSSION: This study demonstrates the feasibility of cascading tests using laboratory protocols and confirms the ability to identify potential cases. However, further studies for HH genotype and urine and stool porphyrin analysis will be necessary to confirm the diagnoses.