From the Guidelines
The recommended method for assessing blood volume and albumin levels using nuclear medicine is the radioiodinated serum albumin (RISA) technique. This procedure involves injecting a small amount of human serum albumin labeled with radioactive iodine (typically I-125 or I-131) intravenously, followed by blood sampling at specific intervals (usually at 10,20, and 30 minutes post-injection) 1. The standard dose is approximately 25 μCi of I-131 albumin for adults. After injection, the radioactive albumin distributes throughout the circulation, and by measuring the dilution of the radiotracer in the blood samples, total blood volume can be calculated. Plasma volume is determined directly from the measurements, while red cell volume is calculated by subtracting plasma volume from total blood volume.
Key Considerations
- The RISA technique provides accurate assessment of blood volume components and albumin distribution, which is crucial in evaluating volume status in conditions like heart failure, cirrhosis, nephrotic syndrome, and critical illness where traditional clinical assessment may be inadequate 1.
- Proper patient preparation is necessary, including thyroid blockade with Lugol's solution or potassium iodide (typically 130 mg daily for 3 days before and 7 days after the test) to prevent thyroid uptake of free radioiodine.
- The use of intravenous albumin should be guided by evidence-based recommendations, taking into account the potential benefits and risks associated with its use, as outlined in guidelines from the international collaboration for transfusion medicine 1.
Clinical Application
- The RISA technique is particularly valuable in critically ill patients, where accurate assessment of volume status is essential for guiding fluid management and optimizing patient outcomes.
- In patients with hypoalbuminemia, the RISA technique can help assess the severity of albumin deficiency and guide treatment decisions, including the use of intravenous albumin 1.
From the Research
Nuclear Medicine Blood Volume Albumin Assay
The nuclear medicine blood volume albumin assay is a technique used to assess blood volume and albumin levels.
- The recommended method for assessing blood volume and albumin levels using nuclear medicine blood volume albumin assay involves the use of technetium-99m-labeled autologous serum albumin ((99m)Tc-HSA) [ 2 ].
- This method has been shown to be safe and effective, with good radiochemical purity and stability [ 2 ].
- Another study compared the reliability of plasma volume measurements by technetium-labeled human serum albumin ((99m)Tc-HSA) with a simultaneously performed plasma volume determination with iodine-labeled human serum albumin ((125)I-HSA), and found that (99m)Tc-HSA can replace (125)I-HSA for single measurements of plasma volume in healthy volunteers [ 3 ].
Blood Volume Analysis
- A new semiautomated system for blood volume analysis is now available, providing highly accurate results for blood volume analysis within only 90 min [ 4 ].
- This system has brought about a surge of clinical interest in using blood volume data for clinical management, and blood volume analysis is poised to enter the clinical mainstream [ 4 ].
- Rapid nuclear medicine blood volume analysis can play a critical role in the diagnosis and management of emergent conditions such as trauma, shock, decompensated heart failure, syncope, and hypertension [ 5 ].
Quantitation of Cerebral Blood Volume
- Technetium-99m diethylenetriaminepentaacetic acid human serum albumin (99mTc-DTPA-HSA) has been used as an agent for quantitation of cerebral blood volume (CBV) [ 6 ].
- The blood retention of 99mTc-DTPA-HSA is sufficient, and its use in the quantitation of CBV omits the need for centrifugation of the blood sample [ 6 ].