Pituitary Disorders: SIADH versus DI

Between SIADH and DI, which one retains and which one excretes too much water? If you’re a bit confused between the two, here’s a quick rundown of the two pituitary disorders that are commonly included in major exams.

Posterior Pituitary (pee-pee) is for ADH

Let’s backtrack a bit and review on the primary function of the posterior pituitary gland.

The posterior pituitary is mainly responsible for the secretion of the antidiuretic hormone (ADH) which is the hormone that triggers either water retention or excretion. Water excretion is in the form of urine (pee-pee).

The antidiuretic hormone, as what we’ve previously discussed, is similar to a turnstile in a train station or a fair that puts water back to be reabsorbed by the body. ADH acts directly on the exit portals to control fluid that goes in or out. Antidiuretic hormone prevents the kidneys from excreting water out of the body.

            Posterior pituitary (pee-pee) = ADH = water excretion or absorption

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

The syndrome of inappropriate antidiuretic hormone (SIADH) is a disorder that has increased antidiuretic hormone. You can remember this by breaking down SIADH to SI and ADH.

Recall your Spanish course wherein “si” in English is “yes.” Now, consider “Si” as “mas” or in English, “more.” So, when applied to SI ADH, you’re basically saying, “Yes ADH, we have more ADH.” This technically means that when you have SIADH, you have increased water reabsorption.

            SIADH = “Si ADH, mas ADH” = Yes ADH, more ADH = increased water reabsorption

The Signs and Symptoms of SIADH

When you think of someone who has SIADH (more ADH), you have to consider that there is increased water retention. So, what happens if there is increased retention of water inside the body?

  1. Fluid volume overload, bounding pulses, jugular vein distention (JVD), increased blood pressure that may lead to headaches
  2. Laboratory values – hemodilution
  3. Edema
  4. Urine analysis – high specific gravity (1.03), brown or dark, odorous urine

Diabetes Insipidus (DI)

Diabetes insipidus is a condition that’s telling your ADH to get lost or die; thus, you can remember diabetes insipidus as DI ADH for “die ADH.” When there is less or no ADH in the body, water is not reabsorbed by the body.

            DI = Die ADH = less or no ADH = increased water excretion

The Signs and Symptoms of DI

So, DI is just the opposite of SIADH. When your client has DI, there is decreased water retention and increased urine output. So, what happens to a client who has DI?

  1. Weak thread pulse, poor skin turgor due to dehydration
  2. Low blood pressure
  3. Laboratory values – hemo-concentrated, increased hemoglobin and hematocrit
  4. Sinkable episodes – very dizzy and faint due to decreased fluid retention
  5. Urine analysis – very low specific gravity (1.005), diluted urine
  6. Increased potassium and sodium in the urine

Points to Remember

In a nutshell, the signs and symptoms of SIADH and DI are mainly because of ADH. When you have too much of ADH, you have SIADH. On the other hand, if you have decreased ADH, you have DI. You can also put it this way:

  • SIADH – In the body and not in the potty
  • DI – In the potty and not in the body

So, that’s the simplified explanation on the difference between SIADH and DI. I hope this cleared up the confusion and helped you distinguishing how SIADH and DI work.

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