Key Benefits

• Spot SIADH by detecting low sodium and using albumin to rule other causes.
• Clarify symptoms like headache, confusion, or nausea by linking them to hyponatremia severity.
• Guide treatment urgency by grading sodium levels and monitoring safe correction over time.
• Differentiate euvolemic SIADH from cirrhosis or nephrotic syndrome using albumin levels.
• Protect brain health by flagging severe hyponatremia that raises seizure and fall risk.
• Track progress by trending sodium during fluid restriction, salt therapy, or vasopressin antagonists.
• Best interpreted with serum and urine osmolality, urine sodium, and your symptoms.

What are SIADH Biomarkers?

SIADH biomarkers are the lab signals that reveal water is being held in the body under the pull of excess antidiuretic hormone (ADH, vasopressin), producing diluted blood and concentrated urine despite overall normal fluid volume. They capture the hormone’s effect rather than an isolated number: blood chemistries that reflect dilution (sodium and osmolality), urine that stays concentrated with salt still being excreted (urine osmolality and urine sodium), and, when needed, a stable proxy for the hormone itself (copeptin, a surrogate for arginine vasopressin). Together they map the kidney’s response—less water excreted, more water kept—and help distinguish SIADH from other explanations for a diluted blood chemistry by showing an ADH-driven water imbalance rather than salt loss or dehydration. Additional checks of whole-body context, such as thyroid and adrenal status, support the picture by ruling out other signals that can mimic SIADH. In short, these biomarkers translate a complex water-regulation disorder into a readable pattern, enabling clear identification of SIADH’s physiology so treatment can be directed at the true driver: inappropriate ADH activity.

Why are SIADH biomarkers important?

SIADH biomarkers are the lab signals that reveal how the brain, kidneys, and blood work together to control water. The central marker is serum sodium, which reflects plasma tonicity and brain safety; albumin helps interpret volume status and the causes of hyponatremia that can mimic SIADH.

Typical serum sodium sits around 135–145, with most people feeling best in the middle. Albumin is generally 3.5–5.0, and tends to be healthiest toward the mid-to-high end because it maintains oncotic pressure and reflects nutritional status. In pregnancy, normal sodium runs slightly lower and albumin is diluted, so interpretation shifts.

When sodium falls, plasma becomes hypotonic and water moves into cells. In SIADH, excess antidiuretic hormone keeps kidneys reabsorbing water despite normal body salt and volume, so sodium drops while albumin often remains normal. The brain is most vulnerable: headache, nausea, unsteadiness, confusion, and seizures can emerge; children and older adults are more seizure- and fall-prone, and premenopausal women face higher risk of cerebral edema. Low albumin, by contrast, points to other hyponatremia states (cirrhosis, nephrotic syndrome, heart failure) rather than SIADH.

Sodium above the reference range usually signals water loss or diabetes insipidus—processes opposite to SIADH—and albumin may appear high from hemoconcentration. Big picture, these biomarkers integrate neuroendocrine control, renal handling, and vascular protein balance; tracking them helps prevent neurologic injury, gait and cognitive effects, bone loss from chronic hyponatremia, and clarifies overlap with thyroid, adrenal, cardiac, hepatic, and renal disorders.

What Insights Will I Get?

Water and sodium balance governs cell volume, nerve signaling, muscle contraction, and blood pressure. In SIADH, excess antidiuretic hormone causes water retention and lower plasma tonicity, which can strain brain and cardiovascular function. At Superpower, we test these biomarkers: Sodium, Albumin.

Sodium is the principal extracellular electrolyte; in SIADH the kidneys reabsorb water out of proportion to solute, diluting serum sodium even though total body sodium is typically normal. Albumin is the dominant plasma protein that maintains oncotic pressure; it is usually normal in SIADH, and when low it suggests alternative, hypervolemic causes of hyponatremia (for example liver or kidney disease) rather than inappropriate ADH.

For stability and healthy function, a steady sodium concentration signals effective osmoregulation and balanced ADH activity. Falling sodium indicates hypotonic stress that especially affects the brain. When sodium is low with normal albumin, the pattern supports euvolemic dilution consistent with SIADH. When sodium is low with reduced albumin, the pattern points toward reduced oncotic pressure and fluid overload as a more likely explanation than SIADH.

Notes: Interpretation is influenced by age, pregnancy (lower physiologic sodium), acute illness, pain, surgery, pulmonary or CNS disease, and medications that raise ADH or impair water excretion (e.g., SSRIs/SNRIs, carbamazepine/oxcarbazepine, thiazides, antipsychotics, desmopressin). Adrenal or thyroid insufficiency can mimic SIADH. Analytical methods (direct vs indirect ion-selective electrodes) and severe hyperlipidemia or hyperproteinemia can artifactually alter sodium results.