Lab Interpretation: Low glucose in adults

ALGORITHM — 

(algorithm 1 and algorithm 2 and algorithm 3)

ADULTS WITH DIABETES — 

In patients with diabetes, the onset of symptoms of hypoglycemia (eg, tremor, palpitations, diaphoresis) may occur at glucose levels <65 mg/dL (3.6 mmol/L), although the specific value varies between and within individuals over time. Symptoms may be absent because of impaired awareness of hypoglycemia. (See "Hypoglycemia in adults with diabetes mellitus".)

Depending on the glucose values and presence or absence of symptoms, management options include:

●Ingesting fast-acting carbohydrates (table 1). If unable to ingest due to neuroglycopenic symptoms (eg, drowsiness, confusion), administer glucagon or intravenous (IV) dextrose.

●Repeating the measurement in the near term (15 to 60 minutes).

●Adjusting the subsequent treatment regimen to prevent recurrent hypoglycemia.

Episodes of severe hypoglycemia (and any glucose <54 mg/dL [3 mmol/L]) should be reviewed in detail to determine their cause and means of prevention. Patients should be told to be especially vigilant following an episode of hypoglycemia since both recognition of hypoglycemia and the counterregulatory response to it will be impaired during this time. (See "Hypoglycemia in adults with diabetes mellitus".)

Long-term management may include the following:

●Individualize glycemic goals to achieve the best degree of mean glycemia that can be accomplished safely

●Tailor treatment regimens to reduce risk of hypoglycemia

●Advise frequent self-monitoring of blood glucose or continuous glucose monitoring

●Provide education for the patient on the recognition and treatment of hypoglycemia

●Check that the patient's blood glucose monitoring equipment is accurately calibrated

●Confirm that fast-acting carbohydrate is being kept available

●Confirm that glucagon is available for emergency use

ADULTS WITHOUT DIABETES

Asymptomatic — A low plasma glucose concentration measured by a laboratory assay (not a glucose meter or continuous glucose monitor) in the absence of symptoms of hypoglycemia suggests the possibility of artifactual hypoglycemia (algorithm 1). Confirm artifactual hypoglycemia by obtaining a plasma glucose in a blood collection tube that contains an antiglycolytic agent. Processing should not be delayed. A reliably measured, severely depressed plasma glucose concentrations (<40 mg/dL [2.2 mmol/L]) in the absence of symptoms may represent shifted glycemic thresholds (hypoglycemia unawareness) due to repeated episodes of hypoglycemia. For the rare patient with this finding, additional evaluation to determine the etiology is necessary. (See "Hypoglycemia in adults without diabetes mellitus: Clinical manifestations, causes, and diagnosis", section on 'Assessment in asymptomatic individuals' and "Hypoglycemia in adults without diabetes mellitus: Determining the etiology", section on 'Supervised testing'.)

Data from continuous glucose monitoring devices are not part of the diagnostic evaluation of hypoglycemia in individuals without diabetes because of poor accuracy in the hypoglycemia range. (See "Hypoglycemia in adults without diabetes mellitus: Clinical manifestations, causes, and diagnosis", section on 'Criteria for a hypoglycemic disorder'.)

Symptomatic — All patients should undergo a timely evaluation to determine the cause(s) of low blood glucose. The patient's overall health status and a thorough clinical history can help identify the most likely cause(s) of hypoglycemia and determine the next steps in evaluation (algorithm 2).

Ill or medicated patient — In an ill or hospitalized patient, the etiology of hypoglycemia may be readily recognized as part of the underlying illness or its treatment (or a prescribing/dispensing error) (table 2). Most patients have multiple reasons for hypoglycemia.

Review the medication administration record to identify prescribing errors, possible causative agents (table 3), and the relationship of medication administration with symptoms.

Initial tests for ill patients with unexplained hypoglycemia may include:

●Basic metabolic panel (glucose, blood urea nitrogen [BUN], creatinine, electrolytes, calcium)

●Hepatic panel (protein, albumin, direct and total bilirubin, alkaline phosphatase, alanine aminotransferase [ALT], aspartate aminotransferase [AST])

●Complete blood count

●8 AM cortisol level

●Thyroid-stimulating hormone (TSH), free thyroxine (T4)

Seemingly well patient — In a well-appearing person without diabetes, the presence of a hypoglycemic disorder is diagnosed based on sequential evaluation and laboratory testing (algorithm 3). If the venipuncture glucose is <65 mg/dL (3.6 mmol/L) at the time of symptoms, an underlying hypoglycemic disorder is possible.

●Initial evaluation

•Review the patient's history in detail to determine the timing of symptomatic hypoglycemia.

•Measure plasma glucose at the time of symptoms to demonstrate that the symptoms are consistent with hypoglycemia, the plasma glucose concentration is low at the same time as symptoms, and the symptoms are relieved when the glucose is raised. If these criteria are met, proceed with supervised testing.

●Supervised testing – The goal of laboratory testing is to determine the mechanism of hypoglycemia (ie, assess whether hypoglycemia is mediated by insulin). Occasionally, blood tests may be obtained during a spontaneous episode of hypoglycemia that occurs under medical supervision. Patients who are fortuitously observed during a symptomatic episode and found to have concurrent hypoglycemia should have the following blood tests performed at the time of hypoglycemia:

•Glucose

•Insulin

•C-peptide

•Beta-hydroxybutyrate

•Proinsulin

•Oral hypoglycemia agent (sulfonylurea and meglitinide)

If the patient is not symptomatic when seen, the diagnostic strategy is to replicate conditions in which hypoglycemia would be expected. If symptoms occur primarily in the fasting state, testing should be performed during a supervised fast. If the patient has a history of exclusively postprandial symptoms, a mixed meal test should be performed.

For patients with endogenous hyperinsulinism (nonsuppressed levels of insulin, C-peptide, and proinsulin; low beta-hydroxybutyrate; and a negative screen for sulfonylureas/meglitinides), measure insulin antibodies to exclude autoimmune hypoglycemia (algorithm 3). Among patients with negative antibodies and endogenous hyperinsulinism, the next step is to obtain abdominal imaging to detect a possible insulinoma. (See "Hypoglycemia in adults without diabetes mellitus: Determining the etiology", section on 'Supervised testing'.)

REFERENCE RANGE — 

The lower limit of the normal fasting plasma glucose value is approximately 70 mg/dL (3.9 mmol/L), but it can vary depending on the patient population and clinical laboratory. Interpretation of a specific abnormal test result should be based upon the reference range reported with that result.

CITATIONS — 

The supporting references for this content are accessible in the linked topics.