Laboratory Evaluation for Hemochromatosis and Polycythemia
For hemochromatosis, start with transferrin saturation and serum ferritin; proceed to HFE genetic testing (C282Y) when transferrin saturation exceeds 45% in females or 50% in males with elevated ferritin, and use MRI to quantify hepatic iron when diagnosis remains unclear. For polycythemia, measure serum erythropoietin (EPO) level, arterial oxygen saturation, and JAK2 mutation status to distinguish polycythemia vera from secondary causes 1, 2.
Hemochromatosis Laboratory Workup
Initial Screening Tests
The diagnostic algorithm begins with two essential tests 1:
- Transferrin saturation (calculated from serum iron and total iron binding capacity)
- Serum ferritin
Proceed to genetic testing when you find:
- Females: transferrin saturation >45% AND ferritin >200 μg/L
- Males: transferrin saturation >50% AND ferritin >300 μg/L 1
Genetic Testing Strategy
Order HFE genotyping for C282Y mutation first in patients of European descent meeting the above biochemical criteria 1. This single test identifies the most common form (C282Y homozygosity) responsible for hereditary hemochromatosis in Northern European populations 3, 4.
Testing for H63D mutation remains controversial and should only be performed in special clinical situations 1. Do not use H63D genotype alone to guide treatment decisions—management of C282Y/H63D compound heterozygotes or H63D homozygotes must be based on phenotypic presentation and additional risk factors, not genotype 1.
Advanced Diagnostic Studies
When genetic testing is negative or inconclusive despite clear iron overload:
- MRI quantification of hepatic iron concentration is the preferred noninvasive method 1, 3
- Cardiac MRI for patients with signs of heart disease or juvenile hemochromatosis 1
- Liver biopsy with iron quantification only when MRI is unavailable or contraindicated 3
Critical threshold: Serum ferritin <1,000 ng/mL at diagnosis identifies patients at low risk for advanced hepatic fibrosis, eliminating the need for liver biopsy in most cases 3.
What NOT to Measure
Do not measure hepcidin levels—this achieved 100% consensus in the 2022 EASL guidelines as it has no established clinical role in diagnosis or management 1, 5.
Polycythemia Laboratory Evaluation
Distinguishing Polycythemia Vera from Secondary Causes
The diagnostic approach differs fundamentally from hemochromatosis 2:
Initial tests:
- Serum EPO level (low or inappropriately normal suggests polycythemia vera)
- Arterial oxygen saturation and carboxyhemoglobin (especially in smokers)
- JAK2 mutation testing (confirms polycythemia vera when positive)
An elevated EPO level strongly suggests secondary polycythemia, but a normal level does not exclude it 2. When family history suggests congenital causes, measure P50 (oxygen pressure at 50% hemoglobin-oxygen saturation)—a low P50 indicates high oxygen-affinity hemoglobinopathy 2.
Secondary Cause Investigation
When EPO is elevated or polycythemia vera is excluded:
- Renal vascular studies to rule out renal artery stenosis
- Imaging of kidneys, liver, and central nervous system when EPO remains persistently elevated
- Question patients about androgen preparations (oral, transdermal, intramuscular) 2
Monitoring During Treatment
Hemochromatosis Monitoring
Track these parameters during phlebotomy therapy 4, 6:
- Serum ferritin to assess iron depletion (target: 50-100 μg/L for maintenance)
- Hemoglobin before each phlebotomy session
- Transferrin saturation periodically
Phlebotomy frequency: Can exceed standard blood donation intervals when prescribed as therapeutic phlebotomy, with proper documentation and provider oversight 6.
Polycythemia Monitoring
Target hematocrit levels vary by underlying cause 2:
- Polycythemia vera: Maintain hematocrit <45% to reduce thrombotic risk
- Cyanotic heart disease or high oxygen-affinity hemoglobinopathy: Judicious phlebotomy to hematocrit ~60% (avoid aggressive phlebotomy due to stroke risk)
- COPD-related polycythemia: Target hematocrit 55-60% for optimal exercise tolerance
Critical Pitfalls to Avoid
Do not assume elevated ferritin equals hemochromatosis—ferritin rises in acute/chronic liver disease, inflammatory states, malignancy, and metabolic syndrome 3, 5. Always check transferrin saturation concurrently, as it remains elevated specifically in iron overload conditions.
Do not order indiscriminate genetic panels—5-15% of phenotypic hemochromatosis cases lack HFE mutations, but testing for rare non-HFE mutations is expensive and rarely changes management 3, 5. Use MRI or liver biopsy instead when HFE testing is negative.
Do not tell patients to "just donate blood"—therapeutic phlebotomy requires a prescribed course with specific frequency, volume, and monitoring parameters that differ from voluntary donation 6.
Recognize the rare coexistence: Hereditary hemochromatosis and JAK2-positive polycythemia vera can occur simultaneously, requiring management of both conditions 7. When a patient with known hemochromatosis develops polycythemia, do not assume it is iron-related—check JAK2 mutation status.