This patient has diabetic ketoacidosis (DKA). The initial management includes aggressive intravenous fluid resuscitation, which has been started. The next crucial step is to address the potassium level before starting insulin. Although the serum potassium is low-normal, the patient has a significant total body potassium deficit due to transcellular shifts and urinary losses. Insulin therapy will drive potassium into cells, worsening the hypokalemia and potentially causing life-threatening arrhythmias. Therefore, if the initial serum potassium is less than 3.3 mEq/L, insulin should be held, and potassium should be repleted first. In this case, with a potassium of 3.1 mEq/L, administering intravenous potassium chloride is the correct next step. Insulin should only be started once the potassium is >3.3 mEq/L.

For non-critically ill hospitalized patients with persistent hyperglycemia (e.g., >180 mg/dL), a scheduled basal-bolus insulin regimen is the standard of care. This approach provides a physiologic insulin replacement with a long-acting (basal) insulin to cover basal metabolic needs and a rapid-acting (bolus) insulin to cover nutritional intake. Sliding-scale insulin as monotherapy is reactive rather than proactive and is associated with poor glycemic control and higher rates of hyperglycemia. An intravenous insulin infusion is typically reserved for critically ill patients in the ICU. Restarting metformin is inappropriate in an acutely ill patient with poor oral intake and risk of renal dysfunction.

The diagnosis of gestational diabetes mellitus (GDM) using the 100-gram OGTT is made if at least two of the four plasma glucose values are met or exceeded. The typical cutoffs are: Fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, and 3-hour ≥140 mg/dL. This patient's 1-hour value (200 mg/dL) and 2-hour value (165 mg/dL) are both above the threshold. Since two criteria are met, the diagnosis is GDM. Her fasting glucose is normal, so she does not have impaired fasting glucose. Overt diabetes would be diagnosed with fasting glucose ≥126 mg/dL or random glucose ≥200 mg/dL with symptoms.

During periods of illness ('sick days'), patients with type 1 diabetes have increased counter-regulatory hormones, leading to increased insulin resistance and hyperglycemia, even with poor oral intake. It is critical to never stop basal insulin, as this can quickly precipitate DKA. The correct advice is to continue the long-acting (basal) insulin, check blood glucose and ketones frequently, stay hydrated, and use supplemental short-acting insulin (correction doses) to manage hyperglycemia. While he may eventually need to go to the emergency department if vomiting persists or ketones worsen, the initial advice should be focused on proper self-management.

For patients with type 2 diabetes and comorbid heart failure with reduced ejection fraction (HFrEF), SGLT2 inhibitors (e.g., empagliflozin, dapagliflozin) have been shown to reduce the risk of cardiovascular death and hospitalizations for heart failure, independent of their glucose-lowering effect. Therefore, adding empagliflozin would provide the most significant benefit for his cardiac condition. Insulin glargine, glyburide, and sitagliptin effectively lower glucose but do not have the specific proven cardiovascular and heart failure benefits of SGLT2 inhibitors. In fact, some older medications like thiazolidinediones are contraindicated in heart failure.

For patients undergoing surgery who are NPO, oral hypoglycemic agents should generally be held on the morning of the procedure to prevent hypoglycemia. Sulfonylureas like glipizide carry a significant risk of hypoglycemia in a fasting state. Metformin is held due to the risk of lactic acidosis in the setting of potential renal dysfunction or hypoperfusion related to surgery and anesthesia. Therefore, the safest approach is to hold both medications. Inpatient glycemic control will be managed with insulin as needed, typically with a correction scale or a basal-bolus regimen if hyperglycemia is significant.

This patient is experiencing recurrent and profound hypoglycemia secondary to a long-acting sulfonylurea (glyburide). Due to the long half-life of these medications, a single bolus of dextrose is often insufficient, and rebound hypoglycemia is common, as seen in this case. The risk is particularly high in the elderly and those with renal insufficiency. The standard of care for sulfonylurea-induced hypoglycemia is hospital admission for continuous intravenous dextrose infusion (e.g., D10W) and frequent glucose monitoring for at least 24-48 hours. Discharging the patient would be unsafe. Octreotide, which inhibits insulin secretion, may also be considered as an adjunct.

For patients with type 2 diabetes and diabetic kidney disease with albuminuria, SGLT2 inhibitors (e.g., dapagliflozin, empagliflozin, canagliflozin) are recommended to reduce the risk of CKD progression and cardiovascular events. These agents have proven renal-protective effects independent of their glucose-lowering capacity and are indicated for patients with an eGFR >30. While GLP-1 receptor agonists like liraglutide also have some renal and cardiovascular benefits, the evidence for slowing CKD progression is strongest for SGLT2 inhibitors in this population. Increasing metformin is not advisable with a reduced eGFR. Pioglitazone does not have the same proven renal-protective effects and can cause fluid retention.

The proper transition from an IV insulin infusion to a subcutaneous regimen requires an overlap between the two methods to prevent a gap in insulin coverage, which could lead to rebound hyperglycemia and ketosis. Intravenous regular insulin has a very short half-life. Long-acting basal insulins (e.g., glargine, detemir) take 1-2 hours to begin working. Therefore, the correct procedure is to administer the first dose of subcutaneous long-acting insulin and then continue the IV infusion for another 1-2 hours before discontinuing it. Stopping the infusion simultaneously with or before the subcutaneous injection would create a period of insulin deficiency.

This patient presents with a high anion gap metabolic acidosis and ketosis, which are hallmarks of DKA. However, her blood glucose is only mildly elevated (190 mg/dL). This constellation of findings in a patient taking an SGLT2 inhibitor (empagliflozin) is characteristic of euglycemic diabetic ketoacidosis (eDKA). SGLT2 inhibitors promote glucosuria, which can mask the significant hyperglycemia typically seen in DKA. Precipitating factors often include illness, surgery, or very low carbohydrate intake. HHS is characterized by severe hyperglycemia and hyperosmolality without significant acidosis. While gastroenteritis can cause acidosis, it would not typically cause ketosis of this magnitude. Metformin-associated lactic acidosis is possible but less likely to present with significant ketosis.