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September 2023 Exam
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Demo Question
A 49-year-old gentleman who is on maintenance hemodialysis 3 times weekly was being reviewed in the clinic. He has a functioning left radiocephalic arteriovenous fistula. He is compliant with his treatment time of 4 hrs each session and denies any symptoms during the consultation.
Investigations reveal:
Haemoglobin 112 g/L (120-10)
Platelet count 299 x 109 /L (150-400)
Serum creatinine 888 umol/L (60-110)
Serum potassium 4.1 mmol/L (3.5-5)
Serum Ferritin 460 ug/L (15-300)
TSAT (transferrin saturation) 19%
He is on 9000 iu of erythropoietin three times weekly.
Which of the investigations would most reliably reflect iron stores?
Bone marrow biopsy
Mean corpuscular haemoglobin concentration
Serum hepcidin 25 level
Serum Iron
Repeat serum ferritin and TSAT
Key Learning Point
Ferritin and TSAT reflect iron stores but there is significant variation 38.2% for TSAT and 15.1% for ferritin. For the same levels of closeness and probability, one sample day would be needed for reticulocyte Hb content, 15 for TSAT, and 3 for ferritin level.
Explanation
Low biological variation renders Hb level, Hct, and reticulocyte Hb content, but not TSAT and ferritin level, suitable for trend analysis using results from 2 successive samples. TSAT and ferritin test results, unlike reticulocyte Hb content, have limited value in evaluating changes in iron status within individual hemodialysis patients. Ferritin and TSAT reflect iron stores but there is significant variation 38.2% for TSAT and 15.1% for ferritin. For the same levels of closeness and probability, one sample day would be needed for reticulocyte Hb content, 15 for TSAT, and 3 for ferritin level. Hepcidin is not useful as a biomarker for iron needs in haemodialysis patients on maintenance erythropoiesis-stimulating agents
