Unit 3: Radioisotopes in haematology
Applied Haematology-II notes · PTU syllabus (BMLS601-18)
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Unit summary
Radioisotopes measure blood volumes and cell survival. This unit covers radioisotopes used in haematology — sources, half-lives and applications — units and apparatus of radiation measurement, measurement of blood, red cell and plasma volume, red cell and platelet life span, radiation hazards and disposal.
After this unit you can
- Describe radioisotopes used in haematology and units of radiation
- Describe radiation measuring apparatus
- Measure blood volume and red cell and platelet survival
- Apply radiation protection and safe disposal
PTU syllabus topics
- Radioactive isotopes used in haematology — definition
- source
- half-life and applications
- units of radiation measurement (curie, millicurie, microcurie, rad)
- apparatus for radiation measurement
- measurement of blood volume
- red cell and plasma volume
- red cell and platelet life span
- radiation hazards
- prevention and disposal of radioactive material
- ⁵¹Cr (chromium-51)
- Red cell survival and red cell volume
- ¹²⁵I albumin
- Plasma volume
- ⁵⁹Fe (iron-59)
- Iron absorption and turnover
- ¹¹¹In (indium-111)
- Platelet life span
- Curie
- 3.7 × 10¹⁰ disintegrations per second
Topic 1
Radioisotopes in haematology
Chromium-51 (⁵¹Cr)
27.7 days
Red cell volume and survival; site of destruction
Iodine-125 (¹²⁵I)
60 days
Plasma volume (labelled albumin), RIA
Iodine-131 (¹³¹I)
8 days
Plasma volume (older)
Indium-111 (¹¹¹In)
2.8 days
Platelet and leucocyte survival and localisation
Technetium-99m (⁹⁹ᵐTc)
6 hours
Red cell labelling for bleeding scans
Iron-59 (⁵⁹Fe)
45 days
Ferrokinetics (marrow iron turnover)
- Sources: nuclear reactors and cyclotrons; ⁹⁹ᵐTc from molybdenum-99 generators.
Topic 2
Units and apparatus of radiation measurement
- Curie (Ci)
- 3.7 × 10¹⁰ disintegrations per second; millicurie and microcurie used for doses
- Becquerel
- 1 disintegration per second (SI)
- Rad
- Absorbed dose of 100 erg/g (SI: gray = 100 rad)
- Rem and sievert
- Dose equivalent for biological effect (1 Sv = 100 rem)
- Apparatus: well-type gamma scintillation counter (samples), Geiger–Müller counter (surveys and spills), dose calibrator (activity before injection), personal dosimeters (TLD badges).
Topic 3
Measurement of blood, red cell and plasma volume
Volume
Amount of tracer injected ÷ concentration after mixing
Red cell volume
⁵¹Cr-labelled red cells; sample after 10–20 minutes
Plasma volume
¹²⁵I-albumin
Total blood volume
Red cell volume + plasma volume (or red cell volume ÷ venous PCV corrected)
- Normal: red cell volume about 25–35 mL/kg (men), plasma volume about 40–50 mL/kg. Uses: distinguishing true polycythaemia (raised red cell mass) from relative polycythaemia (low plasma volume).
Topic 4
Red cell and platelet life span
- Red cell survival (⁵¹Cr): label autologous red cells, re-inject, sample over 2–3 weeks; normal ⁵¹Cr half-time is 25–35 days (because chromium elutes; true life is about 120 days). Shortened in haemolysis; surface counting over spleen and liver shows the site of destruction (useful before splenectomy).
- Platelet survival (¹¹¹In): normal about 7–10 days; shortened in ITP; shows splenic sequestration.
Topic 5
Radiation hazards, prevention and disposal
- Hazards
- Tissue damage, cancer, genetic effects, foetal risk
- Time
- Minimise handling time
- Distance
- Use tongs; radiation falls with the square of distance
- Shielding
- Lead pots and lead-glass screens for γ; acrylic for β
- Monitoring
- TLD badges; area surveys; dose limits (20 mSv per year average for workers)
- Disposal
- Decay in storage for short-lived isotopes (about 10 half-lives) then normal disposal; longer-lived by AERB-approved routes; records maintained
- Regulator in India: the Atomic Energy Regulatory Board (AERB) licenses use and disposal.
Key terms
- Half-life
- Time for radioactivity to halve
- Dilution principle
- Calculating volume from tracer dilution
- Red cell mass
- Total red cell volume
- Surface counting
- External detection of isotope accumulation in organs
- Decay in storage
- Holding waste until radioactivity is negligible
Quick revision
- ⁵¹Cr, ¹²⁵I, ¹³¹I, ¹¹¹In, ⁹⁹ᵐTc, ⁵⁹Fe and uses.
- Curie, becquerel, rad, gray, rem, sievert; counters and dosimeters.
- Dilution principle; red cell and plasma volume; polycythaemia.
- ⁵¹Cr red cell survival (T½ 25–35 days); site of destruction; platelet survival.
- Time, distance, shielding; monitoring; decay in storage; AERB.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.Which isotope is used for red cell survival?
- Q2.Define a curie.
- Q3.State the dilution principle.
- Q4.What is the normal ⁵¹Cr red cell half-time?
- Q5.Name three principles of radiation protection.
- Q6.Who regulates radioisotope use in India?
Long-answer questions
- Q1.Describe the radioisotopes used in haematology and units of radiation.
- Q2.Describe the measurement of blood volume and red cell survival.
- Q3.Describe radiation hazards, protection and disposal.
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