What labs should be monitored as primary care for a patient with potential adrenal insufficiency, particularly one taking pregabalin (lyrica) for neuropathic pain?

Laboratory Monitoring for Adrenal Insufficiency in Primary Care

For patients with established adrenal insufficiency on stable replacement therapy, routine laboratory monitoring should include annual serum sodium and potassium measurements, with additional screening for associated autoimmune conditions. 1

Annual Laboratory Panel

Core electrolyte monitoring:

• Serum sodium and potassium should be checked at least annually to assess adequacy of mineralocorticoid replacement (in primary adrenal insufficiency) and detect under-replacement 1
• Hyponatremia suggests inadequate glucocorticoid or mineralocorticoid replacement 1
• Hyperkalemia (though present in only ~50% of primary adrenal insufficiency cases) indicates mineralocorticoid deficiency 1, 2

Screening for associated autoimmune conditions (primary adrenal insufficiency):

• Thyroid function tests (TSH, free T4) annually, as autoimmune thyroid disease frequently coexists 2, 3
• Fasting glucose or HbA1c to screen for diabetes mellitus 2
• Complete blood count to detect pernicious anemia 2
• Vitamin B12 levels 2, 3
• Tissue transglutaminase antibodies with total IgA if patient has episodic diarrhea or gastrointestinal symptoms, to screen for celiac disease 2

What NOT to Monitor Routinely

Serum and urine cortisol measurements are usually impossible to interpret and not useful for monitoring replacement therapy adequacy 1. Morning cortisol measurements in patients actively taking corticosteroids are not diagnostic because the assay measures both endogenous cortisol and therapeutic steroids 2.

Clinical Assessment Takes Priority Over Labs

Physical examination findings are more valuable than laboratory values for assessing replacement adequacy: 1

• Normal skin color indicates sufficient replacement (hyperpigmentation suggests under-replacement in primary adrenal insufficiency) 1
• Blood pressure should be normal; postural hypotension reflects insufficient mineralocorticoid therapy 1
• Stable weight is the goal; weight loss suggests insufficient glucocorticoid dosing or intercurrent illness 1

Special Monitoring Situations

If suspecting hydrocortisone under-replacement despite normal labs:

• A morning cortisol day curve (before and 2,4, and 6 hours following the morning dose) can assess absorption and elimination patterns 1
• This is only useful when suspecting rapid cortisol disappearance requiring more frequent dosing 1

For primary adrenal insufficiency on fludrocortisone:

• Assess for salt cravings, orthostatic blood pressure changes, and peripheral edema clinically 2, 3
• Plasma renin activity can be measured if mineralocorticoid dose adjustment is needed 2

Critical Pitfall to Avoid

Never attempt to "wean" or discontinue hydrocortisone in patients with confirmed primary or secondary adrenal insufficiency from non-iatrogenic causes—these conditions are permanent and stopping replacement therapy will precipitate life-threatening adrenal crisis 2. The only exception is iatrogenic adrenal insufficiency from exogenous steroid use, which may recover after prolonged discontinuation 2.

Additional Long-Term Monitoring

Bone mineral density should be assessed every 3-5 years to monitor for complications of glucocorticoid therapy 2.

Regarding Pregabalin (Lyrica)

There is no evidence that pregabalin affects adrenal function or requires additional laboratory monitoring in patients with adrenal insufficiency. Standard monitoring protocols apply regardless of concurrent pregabalin use for neuropathic pain.