If plasma volume is determined to be 15 L, what is the likely reason?

Determining that plasma volume is 15 L points toward the presence of an anomaly, and in this context, the most indicative reason is the infiltration of the tracer. Infiltration occurs when the radiopharmaceutical used in a study leaks out of the intended vascular system, leading to inaccurate measurements. This leakage could cause an artificial elevation in plasma volume as the tracer does not remain confined to the blood vessels.

When tracing plasma volume, the accuracy of the measurement can be compromised by factors such as improper administration of the tracer. Infiltration alters the distribution of the tracer, resulting in a misleading representation of the actual plasma volume.

Other options would not typically lead to such a high plasma volume measurement. Overhydration may increase plasma volume, but it usually wouldn't reach such extremes. Similarly, completion of a satisfactory study would normally indicate expected values based on the patient's condition and preparation. Not fasting could potentially alter certain metabolic evaluations, but it typically would not directly result in such a significant increase in plasma volume measurements. Thus, infiltration of the tracer is the most plausible explanation for the finding of an elevated plasma volume.