Labeled Leukocyte (WBC) Scintigraphy¹¹¹In-oxine · ⁹⁹ᵐTc-HMPAO (autologous WBC)
In-111-oxine and Tc-99m-HMPAO white-cell imaging, with marrow subtraction for osteomyelitis
Quick Answer
Labeled-leukocyte scintigraphy images neutrophil accumulation, making it the nuclear reference for neutrophil-mediated infection — prosthetic-joint and vascular-graft infection, diabetic-foot osteomyelitis, and postoperative abscess — where FDG and bone scan are less specific. Autologous white cells are radiolabeled ex vivo with In-111-oxine or Tc-99m-HMPAO and reinjected; focal uptake that intensifies over time (dual-time) indicates infection. In the marrow-containing skeleton, WBC uptake must be read against a Tc-99m-sulfur-colloid marrow scan — infection is WBC-positive but marrow-negative (spatial mismatch).
Background & Mechanism
The patient's own leukocytes (chiefly neutrophils) are separated, labeled with a lipophilic complex that crosses the cell membrane (In-111-oxine or Tc-99m-HMPAO), and reinjected. Labeled cells migrate to sites of active neutrophilic inflammation/infection. Because it tracks neutrophils, it is most useful for pyogenic infection and less so for chronic granulomatous, tuberculous, or spinal infection (where FDG/gallium are preferred).
In-111-oxine vs Tc-99m-HMPAO
| Feature | In-111-oxine | Tc-99m-HMPAO |
|---|---|---|
| Photons / half-life | 171, 245 keV / 2.8 d | 140 keV / 6 h |
| Image quality | Lower count | Higher count/resolution |
| Timing | 24-h delayed ideal (stable label) | Earlier (~1–4 h); label elutes over time |
| Normal distribution | Liver, spleen, marrow | Liver, spleen, marrow + GI/renal/gallbladder excretion |
| Best for | Delayed imaging; abdomen (no bowel activity) | Extremities/quick studies; avoid late abdomen (physiologic bowel/renal) |
Key distinction: Tc-99m-HMPAO shows physiologic bowel, urinary, and gallbladder activity over time (eluted tracer), so it is poor for abdominal infection on delayed images — In-111 has no bowel excretion and is preferred there.
Marrow Subtraction (the osteomyelitis technique)
Normal hematopoietic marrow takes up labeled WBCs, so in the skeleton a positive WBC focus could be marrow, not infection. The solution is a paired Tc-99m-sulfur-colloid marrow scan (colloid marks marrow but not infection):
- Infection = WBC-positive / marrow-negative (spatial incongruence/mismatch).
- Normal or altered marrow = WBC and colloid distributions match (congruent).
This dual-tracer (WBC + marrow) technique is the most specific nuclear test for complicating osteomyelitis (prosthesis, neuropathic/Charcot foot, post-surgical bone).
Indications
- Prosthetic joint infection and vascular graft infection.
- Diabetic-foot / neuropathic (Charcot) osteomyelitis (with marrow subtraction).
- Postoperative abscess / occult pyogenic infection, inflammatory bowel disease activity (In-111).
Where It Underperforms (use FDG/gallium instead)
- Spine / vertebral osteomyelitis — unreliable (marrow/photopenia confounders) → FDG-PET or gallium.
- Chronic, granulomatous, tuberculous infection — neutrophil-poor.
Interpretation & Reporting
- Perform dual-time imaging; increasing focal uptake = infection, fading/stable = less likely.
- For bone, obtain and co-register the marrow scan; call infection on WBC/marrow mismatch.
- Report agent, timing, and (for skeleton) the marrow-subtraction result.
Common Pitfalls
- Reading skeletal WBC uptake without a marrow scan (marrow mimics infection).
- Using Tc-99m-HMPAO for delayed abdominal imaging (physiologic bowel/renal/gallbladder activity).
- Applying WBC imaging to the spine or chronic granulomatous infection (use FDG/gallium).
- Recent antibiotics / poor labeling / low neutrophil count reducing sensitivity.
Board Pearls
Labeled-leukocyte scintigraphy images neutrophil accumulation — the nuclear reference for pyogenic infection (prosthetic-joint/vascular-graft infection, diabetic-foot osteomyelitis). In the marrow-containing skeleton, read WBC against a Tc-99m-sulfur-colloid marrow scan: infection is WBC-positive but marrow-negative (spatial mismatch) — the most specific nuclear test for complicating osteomyelitis.
Tc-99m-HMPAO (140 keV, higher resolution, early imaging) shows physiologic bowel/renal/gallbladder activity over time — poor for delayed abdominal infection; In-111-oxine (24-h delayed, no bowel excretion) is preferred in the abdomen. Both label autologous neutrophils ex vivo.
WBC imaging underperforms in the spine and in chronic/granulomatous/tuberculous infection (neutrophil-poor) — use FDG-PET or gallium there. Sensitivity falls with recent antibiotics, poor labeling, or low neutrophil counts. Read dual-time: increasing focal uptake favors infection.
Related Pages
- Disease: Osteomyelitis / diabetic foot; tracer: Tc-99m-sulfur colloid (marrow scan); contrast: Gallium-67, FDG (spine/chronic infection); overview: Infection & inflammation imaging.
Figure / Diagram Suggestions
- A WBC-vs-marrow (sulfur colloid) mismatch teaching pair (infection) vs congruent (marrow).
- An In-111 vs Tc-99m-HMPAO property/timing comparison.
Self-Check
Q1. How does marrow subtraction distinguish osteomyelitis from normal marrow uptake?
Answer: Infection is WBC-positive but sulfur-colloid (marrow)-negative — a spatial mismatch; normal/altered marrow shows congruent WBC and colloid distributions.
Q2. Why is Tc-99m-HMPAO WBC poor for delayed abdominal infection, and what is preferred?
Answer: Eluted tracer produces physiologic bowel/renal/gallbladder activity over time; In-111-oxine (no bowel excretion, 24-h imaging) is preferred in the abdomen.
Q3. In which infections does labeled-WBC underperform, and what replaces it?
Answer: Spine/vertebral and chronic/granulomatous/tuberculous (neutrophil-poor) infection — use FDG-PET or gallium.
Q4. What cell type does the study primarily track, and what does that imply about its best use?
Answer: Neutrophils — so it excels in acute pyogenic infection and is less useful for neutrophil-poor chronic/granulomatous disease.
Evidence & sources
https://nuc.med/labeled-leukocyte-scintigraphy/ Report an issue