SIADH: Clinical Indicators, Documentation, and Coding Guidance

Syndrome of Inappropriate Antidiuretic Hormone (SIADH) occurs when the pituitary gland releases excessive antidiuretic hormone (ADH), leading the body to retain fluid and dilute sodium levels in the bloodstream. This condition causes hyponatremia and hypo-osmolality, often triggering a complex clinical picture.

Common Causes and Risk Factors for SIADH

What Causes SIADH?

SIADH can develop in response to several underlying conditions or external factors:

• CNS disturbances: Stroke, hemorrhage, infection, and trauma can trigger abnormal ADH release.
• Cancer: Especially small cell lung cancer, extrapulmonary small cell carcinomas, head and neck cancers, and olfactory neuroblastomas.
• Medications: SSRIs, NSAIDs, opiates, some antineoplastic drugs, ciprofloxacin, haloperidol, and high-dose imatinib.
• Surgery: Often linked to pain response.
• Hormonal deficiencies: Including hypothyroidism and hypopituitarism.
• Exogenous hormone use: Vasopressin, desmopressin, and oxytocin.
• HIV infection
• Hereditary SIADH

Diagnostic Criteria for SIADH (Schwartz and Bartter)

A diagnosis of SIADH typically includes:

• Serum sodium < 135 mEq/L
• Serum osmolality < 275 mOsm/kg
• Urine sodium > 40 mEq/L
• Urine osmolality > 100 mOsm/kg
• Normal skin turgor and blood pressure (absence of clinical volume depletion)
• Exclusion of other hyponatremia causes
• Correction of sodium levels via fluid restriction

Important Note: Code only the SIADH, not the hyponatremia, as hyponatremia is considered integral to the disease process.

Clinical Scenario Illustrating SIADH

A 68-year-old male presents to the ED with confusion, nausea, and a 12-pound weight gain over the past week. He was diagnosed with small cell lung cancer two months ago.

Vitals:

• BP: 160/90 mmHg
• HR: 110 bpm

Labs:

• Serum sodium: 122 mEq/L
• Serum osmolality: Decreased
• Urine: Elevated osmolality and high sodium concentration

Indicators Supporting a Diagnosis of SIADH

• Hyponatremia: Sodium level of 122 mEq/L
• Diluted Serum Osmolality: From water retention
• Concentrated Urine: High osmolality and sodium levels despite low serum sodium
• Recent Weight Gain: 12 lbs in one week, pointing to fluid overload
• Underlying Malignancy: Small cell lung cancer is a well-known cause of ectopic ADH production

CDI Documentation Tips for SIADH

1. Accurate Diagnosis

• Clearly state “SIADH” and link it to the underlying cause, such as cancer.

2. Clinical Findings

• Review provider and nursing notes for symptoms like confusion, nausea, and fluid retention.
• Confirm vital signs and weight gain.
• Include lab values: sodium, serum/urine osmolality, and urine sodium.

3. Treatment Plan

• Document fluid restriction orders.
• Check MAR for medications such as vasopressin receptor antagonists.
• Note any improvements in symptoms and lab values after treatment.

Tip: High blood glucose can artificially lower serum sodium levels. Use a sodium correction calculator to determine the true sodium level.