Venous sampling is a minimally invasive diagnostic procedure that measures substance levels, like hormones, directly from veins connected to a specific organ. Unlike a standard blood draw from an arm, which shows general levels throughout the body, this technique provides a targeted snapshot. Its purpose is to identify the precise origin of a hormonal imbalance. By accessing blood as it leaves a gland, physicians can determine if that source is responsible for an excess.
Diagnostic Goals of Venous Sampling
Venous sampling is used when other tests, like general blood work and imaging scans, confirm the body is producing too much of a hormone. The procedure answers the remaining question: where the problem is located. This information is necessary for determining the correct course of treatment.
A common application is for primary aldosteronism, where the adrenal glands produce excess aldosterone, a hormone that controls blood pressure. Adrenal venous sampling (AVS) determines if a single, benign tumor on one adrenal gland is the cause, or if both glands are overactive. This distinction guides treatment; a single tumor can be surgically removed, while overactivity in both glands is managed with medication. Without AVS, imaging alone can be misleading, as small tumors may not be visible.
Another use is in diagnosing the cause of Cushing’s syndrome, a condition of excess cortisol. When tests show high levels of the hormone ACTH are driving cortisol production, sampling locates the source of the ACTH. The procedure, inferior petrosal sinus sampling (IPSS), differentiates between a pituitary gland tumor (Cushing’s disease) and an ectopic tumor elsewhere in the body. Pinpointing this source is necessary before considering surgical intervention.
The Venous Sampling Procedure
The procedure begins with specific preparations. Patients are instructed to fast for several hours beforehand and may need to temporarily stop taking certain medications that affect blood pressure or hormone levels. This ensures the test results are accurate. Prior to the procedure, imaging tests may be completed to provide a roadmap for the physician.
The test takes place in an interventional radiology suite and can last several hours. The patient receives light sedation to remain comfortable but is awake. After applying a local anesthetic, the radiologist makes a small puncture in the femoral vein in the groin and inserts a catheter, a thin, flexible tube.
Using a live X-ray called fluoroscopy and a contrast dye to make the veins visible, the radiologist guides the catheter to the target veins. For adrenal sampling, this involves navigating to the veins draining each adrenal gland. Once in position, blood samples are drawn from these targeted locations and from a peripheral vein for comparison. In some cases, a stimulating agent like synthetic ACTH may be administered to observe how the glands respond.
After collecting the samples, the catheter is removed. A nurse or technologist applies firm pressure to the insertion site to prevent bleeding and bruising. The patient is then required to lie flat for several hours for observation. The most common aftereffect is minor bruising or soreness at the insertion site.
Understanding the Results
Interpreting the results involves comparing hormone levels from the targeted veins against the general (peripheral) blood sample. A significantly higher concentration of the hormone in blood from one location reveals the problem area. For instance, in adrenal venous sampling for primary aldosteronism, the lab measures both aldosterone and cortisol levels. The aldosterone-to-cortisol ratio is calculated for each adrenal vein, and a much higher ratio on one side indicates a single gland is the culprit, a finding known as lateralization.
Similarly, for Cushing’s syndrome, a high ACTH level in the petrosal sinus veins points toward a pituitary source. This definitive information allows the medical team to distinguish between conditions requiring surgery and those best managed with medication, leading to a targeted treatment plan.