SIADH vs DI Practice Questions with Answers and NCLEX® Review

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) and Diabetes insipidus (DI) can be challenging to distinguish from each other at first glance. However, several key differences between them will help you, as a nurse, make an accurate diagnosis and care plan.

SIADH vs DI Practice Questions with Answers and Practice Questions

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    Introduction to SIADH vs DI

    SIADH is a condition where there’s an overabundance of the hormone vasopressin (also called antidiuretic hormone), which regulates the amount of water in the body. This causes the client to become dehydrated and retain excess water in their body tissues, which results in hyponatremia (low sodium levels) and hypovolemia (low blood volume).

    DI is a disease that causes too much urine production because the body doesn’t produce enough ADH (antidiuretic hormone). This results in polyuria (increased urination), which can result in dehydration if left untreated.

    Both conditions involve the kidneys, but there are some key differences. In SIADH, excess water is retained by the body, while in DI, insufficient water is produced to keep up with what’s being excreted.

    DI and SIADH Pathophysiology

    One of the main differences between these two conditions is that SIADH is caused by increased antidiuretic hormone (ADH) in the kidneys. In contrast, DI is caused by a decrease in the amount of ADH.

    In SIADH, there is too much ADH, which causes the body to produce too much urine and not conserve enough water. This results in dehydration, low blood pressure, and low sodium levels.

    In DI, there isn’t enough ADH, so the body doesn’t produce enough urine, resulting in dehydration, high blood pressure, and high sodium levels. DI occurs when there is a lack of ADH, so the kidneys cannot reabsorb water from the urine. This causes increased urination, as well as dehydration, which can lead to serious health problems if not treated.

    With DI clients, their kidneys aren’t making enough ADH. This leads to a loss of fluids, which can result in excessive urination and dehydration.

    SIADH occurs when the body produces too much antidiuretic hormone (ADH), which causes the body to retain water. This leads to low blood sodium levels and high blood potassium levels. In SIADH clients, their kidneys are producing too much antidiuretic hormone (ADH), which helps retain water. This can lead to dehydration, especially if they’re not drinking enough fluids.

    Causes of SIADH and DI

    The most common cause of SIADH is a brain tumor in the pituitary gland. Other causes include certain cancers, head injuries, infections, and some medications.

    SIADH is caused by the kidneys not filtering the fluid properly. This results in the body producing too much urine, which dilutes the blood. As a result, this can cause swelling in the brain and lungs.

    DI is caused by an imbalance of two hormones: vasopressin and AVP (vasopressin precursor). Vasopressin controls how much water leaves the body through urine, and AVP helps regulate blood pressure and blood volume.

    When these hormones are out of balance, the body loses too much water through urine or does not retain enough water to stabilize blood pressure.

    Are you
    to take the

    Labs for SIADH and DI

    Remember these lab values for SIADH and DI:


    • Urine osmolarity >300 mOsm/kg (with a low serum sodium level)
    • Urine sodium level <20 mEq/L (with a high serum osmolarity)
    • Urine Na+ >20 mEq/L, with urine osmolality >300 mOsm/kg (with a low serum sodium level)
    • Hyponatremia with increased plasma tonicity
    • Hypernatremia with decreased plasma tonicity
    • Hypernatremia with decreased plasma tonicity in the absence of DI or SIADH
    • Serum sodium < 135 mmol/L, serum chloride < 96 mmol/L, urine osmolality > 300 mosm/kg (or urine specific gravity > 1.020)

    Memory tricks:

    • SOAKED Inside “Low & Liquidy” Labs
    • HYPO osmolality (LOW)
    • HYPOnatremia below 135 Na+ (LOW)
    • STICKY thick urine” Outside -> LOW urine output (STOPS urine)
    • HIGH specific Gravity 1.030+


    • Serum sodium < 125 mmol/L, serum chloride < 95 mmol/L, urine osmolality < 300 mosm/kg (or urine specific gravity < 1.010)
    • Urine osmolarity >300 mOsm/L in the presence of normal serum electrolytes and normal body weight (>45 kg)

    Memory tricks:

    • Dry Inside “High & Dry” Labs
    • HYPER osmolality (HIGH)
    • HYPERnatremia over 145 Na+ (HIGH)
    • DIluted OUTSIDE ‘’High urine output (Drains urine)
    • LOW specific Gravity 1.005
    • D • Desmopressin/Vasopressin (synthetic ADH)
    • D • Decreases Urine Output “Pressin” the BP Up!
    • CAUTION: “Headaches” Priority!
    • Low Na+ (135 or less) > Seizures > DEATH!

    DI and SIADH Treatment

    SIADH and DI are treated with a combination of fluids and medication.

    For SIADH, the primary treatment is to restrict fluids and replace sodium as prescribed by the health care provider (HCP). Monitor for fluid volume excess. If the patient has too much fluid volume overload, that can lead to pulmonary edema (which is life-threatening), so it’s important to monitor labs along with intake and output.

    For DI, the primary treatment is to maintain adequate fluid intake and administer medications as prescribed by the HCP. As a nurse, you should monitor for signs of dehydration, such as intake and output, skin turgor, and dry mucous membranes.

    Another important nursing assessment is obtaining vital signs and monitoring neurologic and cardiovascular status. Maintain safety if there is a change in the level of consciousness (LOC).

    DI and SIADH Medications

    The most common medications that clients with SIADH and DI receive are Vasopressin and Desmopressin (DDAVP).

    Vasopressin is a medication used for managing DI that helps to regulate the amount of water in the body. DDAVP is a synthetic version of vasopressin that helps to increase urine output and supplement low vasopressin levels.

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    SIADH vs DI Conclusion

    The kidneys are involved in both SIADH and DI – however there are some significant distinctions. In SIADH, the body holds onto extra water, but in DI, not enough water is created to match the amount being expelled.

    The fact that SIADH is brought on by elevated antidiuretic hormone (ADH) in the kidneys is one of the primary distinctions between these two diseases. DI, on the other hand, is brought on by a reduction in ADH levels.

    Fluids and medications are used in conjunction to treat SIADH and DI. In addition to all of this, nurses also look for dehydration.

    Patients with SIADH and DI are most frequently prescribed vasopressin and desmopressin (DDAVP).


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