CCRN Endocrine Review: DKA vs HHS, DI vs SIADH, Adrenal and Thyroid Crises

What the CCRN (Adult) test plan lists under endocrine

The Adult CCRN test plan for exams on and after November 12, 2025, places endocrine problems in category C, which is 21% of the exam and also covers hematology and immunology, GI, renal and genitourinary, and integumentary problems. The endocrine list names adrenal insufficiency, diabetes insipidus, type 1 and type 2 diabetes, DKA, hyperglycemia, HHS, SIADH, and thyroid disorders. The 2025 list no longer names acute hypoglycemia, which the 2020 list did.

The clinical points below come from MSD Manual chapters reviewed between June 2025 and January 2026, and from a 2022 endocrine position statement.

Central diabetes insipidus vs SIADH at the bedside

Both problems involve vasopressin (ADH), and they move water in opposite directions. The urine settles most exam items.

Two details change answers. First, pituitary surgery and head injury appear on the cause lists for both conditions, so the setting alone does not decide; the urine and the sodium trend do. Second, sodium in SIADH must not be corrected too fast. MSD's SIADH chapter warns that too-rapid correction risks osmotic demyelination and limits the rise to no more than 8 mEq/L in the first 24 hours.

About the name. The AACN test plan still says "diabetes insipidus." In 2022, a working group of endocrine societies, endorsed by the Endocrine Society and others, proposed renaming central DI arginine vasopressin deficiency (AVP-D) and nephrogenic DI arginine vasopressin resistance (AVP-R), keeping the old name in parentheses during the transition. One reason they gave: confusion with diabetes mellitus has led to desmopressin being withheld from patients with central DI, with serious harm, including deaths. On a CCRN item, read "DI" as the water-balance disorder, never as a glucose problem.

A DI vignette after head injury

This example is original. On the second day after a severe head injury with a basal skull fracture, a patient's urine output rises from about 80 mL/h to over 300 mL/h for three consecutive hours. The urine looks like water, the specific gravity is 1.003, and the serum sodium has gone from 143 to 150 mEq/L since morning. The patient is receiving no diuretic and has no hyperglycemia.

Every clue points the same way: a large volume, very dilute urine, and a sodium that is climbing because free water is being lost. The nurse reports the trend now and anticipates desmopressin with replacement of the urine losses. Fluid restriction would be the SIADH answer and would make this patient worse.

Contrast that with a patient six days after a subarachnoid hemorrhage whose sodium drifts from 138 to 128 mEq/L, whose urine is concentrated, and who shows no signs of dehydration or fluid overload. That pattern fits SIADH, one of the CNS causes MSD lists.

The free 20-question CCRN (Adult) set includes a central DI item after pituitary surgery, so with the comparison above in hand, test your DI-versus-SIADH call on the post-pituitary case → and see why each of the other three treatments fails.

DKA vs HHS: two hyperglycemic emergencies

Potassium comes before insulin. MSD's DKA chapter says insulin is withheld while the serum potassium is low, because insulin moves potassium into cells, and that potassium is checked hourly once insulin starts. HHS follows the same potassium approach. Your unit's protocol sets the exact potassium level; know where to find it.

Overlap is common. MSD notes that features of both DKA and HHS often appear together. When ketonemia and acidosis are significant, insulin follows the DKA protocol. MSD also notes that some guidelines no longer require a specific glucose level to diagnose DKA, so do not rule out DKA just because the glucose is less extreme than you expected.

Two DKA safety points. Bicarbonate is not given routinely, partly because it may contribute to cerebral edema. Cerebral edema is rare in adults, but headache and a fluctuating level of consciousness during treatment should be reported at once. The ABG guide shows how to calculate and read the anion gap these patients present with.

Adrenal crisis: treat on suspicion

MSD's Addison disease chapter (full review January 2026) describes adrenal crisis as profound weakness with peripheral vascular collapse, severe pain in the abdomen, lower back, or legs, and hypotension that can resist both fluids and vasopressors. Temperature may be low, or there may be high fever when infection triggered the crisis. Typical labs are a low sodium, a high potassium, a low bicarbonate, and a high BUN, and hypoglycemia can follow fasting.

Triggers include acute infection, trauma, surgery, and heavy sweating. Starting thyroid hormone in a patient with undiagnosed adrenal insufficiency can also set off a crisis.

The exam point is timing. MSD says therapy starts immediately on suspicion and that any delay, including for testing, may be fatal. A single blood sample for cortisol and ACTH can be drawn, but the stimulation test waits until the patient has recovered. Emergency treatment includes an IV glucocorticoid, usually hydrocortisone, and prompt isotonic fluid resuscitation, with glucose correction if needed. An option that says "wait for the cortisol result before giving the steroid" is wrong.

Thyroid storm: recognition and treatment order

Thyroid storm is an acute, life-threatening form of untreated or inadequately treated severe hyperthyroidism (MSD hyperthyroidism chapter, full review January 2026). Precipitants include infection, trauma, surgery, embolism, DKA, and preeclampsia.

Look for fever, marked weakness, agitation or altered consciousness, GI symptoms, and marked tachycardia or cardiovascular collapse. The key drug-order rule is to give a thionamide before iodine; iodine is generally delayed at least one hour so it does not provide substrate for new hormone synthesis. Glucocorticoids, cooling, fluids, and treatment of the trigger proceed as clinically indicated rather than waiting through a rigid sequence. Beta-blockade requires particular caution in decompensated heart failure or shock. Follow the treating team's protocol.

How to study the endocrine part of category C

Start with the DI-versus-SIADH table, because the same urine-and-sodium logic answers several kinds of stems. Then learn DKA and HHS as a comparison, not as two lists. Adrenal crisis and thyroid storm need fewer facts but punish hesitation, so practice saying the first action out loud. Use the Adult test plan guide to identify the remaining category C topics for your course materials.