4 Glucose and Endocrine Laboratory Values

Interpreting laboratory results

Use the reference interval and critical-value policy printed by the laboratory. Ranges can vary with method, age, pregnancy, and clinical context. Interpret results alongside symptoms, trends, medications, and other tests: an out-of-range result is not by itself a diagnosis, and an in-range result does not rule out illness.

The glucose cutoffs below apply to nonpregnant adults and are principally diagnostic thresholds, not universal bedside treatment targets. Without unequivocal symptoms, an abnormal result generally needs confirmation.

Glucose tests and diagnostic cutoffs

For nonpregnant adults, the usual interpretations are:

• Fasting plasma glucose: after at least $8$ hours of fasting, normal is $\leq 99\ \text{mg/dL}$, prediabetes is $100\text{–}125\ \text{mg/dL}$, and diabetes is $\geq 126\ \text{mg/dL}$. This is a single-time-point measure; illness, stress, and other factors can affect it.

• A1C: normal is below $5.7\%$, prediabetes is $5.7\text{–}6.4\%$, and diabetes is $\geq 6.5\%$. It estimates average glucose over roughly $2\text{–}3$ months, but conditions affecting red blood cells can make it misleading.

• Two-hour oral glucose tolerance test: measured $2$ hours after a $75$-g glucose drink, normal is $\leq 139\ \text{mg/dL}$, prediabetes is $140\text{–}199\ \text{mg/dL}$, and diabetes is $\geq 200\ \text{mg/dL}$.

• Random plasma glucose: a result of $\geq 200\ \text{mg/dL}$ with classic symptoms can support diagnosis. These symptoms include increased thirst or urination and unexplained weight loss.

Recognizing and responding to hypoglycemia

Symptoms may include sweating, tremor, hunger, palpitations, confusion, seizure, or loss of consciousness. A glucose below $70\ \text{mg/dL}$ is an alert value; below $54\ \text{mg/dL}$ is clinically significant. Severe hypoglycemia is defined by the need for another person’s help, regardless of the measured glucose.

Respond promptly:

1. Assess the patient, verify the result when appropriate, and check mental status and ability to swallow. Do not delay treatment for a symptomatic patient while repeating a test.

2. If the patient is awake and can swallow safely, follow facility protocol. A common approach is $15$ g of fast-acting carbohydrate, followed by a glucose recheck in $15$ minutes; repeat if glucose remains below $70\ \text{mg/dL}$.

3. If the patient cannot swallow, is severely confused, is seizing, or is unconscious, give nothing by mouth. Activate emergency assistance and administer glucagon or IV dextrose as authorized by protocol or order. Recheck glucose and reassess. Protect the airway, and place an unconscious patient on their side if appropriate.

4. Notify the responsible clinician, investigate possible causes such as insulin, other glucose-lowering medicines, missed meals, or renal impairment, and document actions and response. Continue monitoring for recurrence.

Hyperglycemia and hyperglycemic crises

High glucose can cause thirst, frequent urination, dehydration, blurred vision, and fatigue. A high reading alone does not establish a hyperglycemic crisis; assess the patient and the full clinical picture.

Diabetic ketoacidosis (DKA) involves ketones and metabolic acidosis and can occur with glucose as low as $200\ \text{mg/dL}$, especially with SGLT2-inhibitor use or pregnancy. Hyperglycemic hyperosmolar state (HHS) typically involves much higher glucose, severe dehydration, and altered cognition.

Escalate urgently for vomiting, abdominal pain, deep or labored breathing, marked dehydration, positive ketones, worsening weakness, or altered mental status, regardless of whether glucose seems extremely high. Notify the clinician or rapid-response team according to acuity and local policy. Check glucose and ketones as ordered, monitor vital signs and mental status, and prepare for urgent evaluation and prescribed fluids, insulin, and electrolyte monitoring. Do not independently give extra insulin outside an order or protocol. DKA and HHS are life-threatening emergencies.

Interpreting selected endocrine tests

Interpret thyroid tests together with one another, symptoms, medications, and the laboratory’s reference ranges. High TSH with low free T4 commonly indicates primary hypothyroidism; low TSH with high free T4 commonly indicates hyperthyroidism. A TSH result alone may not identify the cause, and pituitary disease or severe illness can complicate interpretation.

A typical free T4 reference interval is about $0.8\text{–}1.9\ \text{ng/dL}$, but use the reporting laboratory’s interval. Pregnancy, acute illness, and some medicines or supplements can affect free T4 results.

A commonly cited morning serum cortisol interval at about 8 a.m. is $5\text{–}25\ \text{mcg/dL}$. Timing, assay, and clinical context matter. A low value may prompt evaluation for adrenal insufficiency, but one cortisol result does not establish the cause; stimulation testing may be needed.

Recognizing hormone-related emergencies

Possible adrenal crisis can involve hypotension or shock, severe weakness, vomiting or abdominal pain, dehydration, hyponatremia, hyperkalemia, or hypoglycemia. Concern is heightened in someone with known adrenal insufficiency or recent long-term steroid use. Activate emergency response and notify the clinician immediately. When adrenal crisis is suspected, treatment should not wait for confirmatory testing; immediate stress-dose IV hydrocortisone is recommended for severe symptoms or crisis.

Possible thyroid storm involves severe thyrotoxic symptoms with high fever, marked tachycardia or arrhythmia, agitation or delirium, heart failure, or gastrointestinal symptoms. Treat it as an emergency: activate rapid response or emergency care and monitor airway, circulation, temperature, and cardiac rhythm.

Possible myxedema crisis is severe hypothyroidism with hypothermia, slow or inadequate breathing, hypotension, low glucose, or reduced responsiveness. It requires emergency hospital care.

Managing critical results

For any critical result, follow local policy. Promptly assess the patient and verify patient and specimen identity. Communicate the result through the required escalation chain, document who was notified and when, and reassess after interventions. Do not delay escalation to resolve a nonurgent question about a reference range.