Table 1.
Potential Sources of Error in Biochemical Testing
| Test | Causes of False Positives | Causes of False Negatives |
|---|---|---|
| Dexamethasone suppression test | Drugs that increase dexamethasone metabolism Anti-epileptics Pioglitazone Rifampin Increased CBG Estrogen (ie OCPs, pregnancy) |
Drugs that impair dexamethasone metabolism Aprepitant Cimetidine Diltiazem Fluoxetine Itraconazole Ritonavir Decreased CBG Nephrotic syndrome Critical illness Malnutrition Liver disease |
| Salivary cortisol | Contamination by topical steroids Licorice ingestion Shift workers Tobacco use |
|
| Urine free cortisol | >5L/day fluid intake | CrCl <60ml/min Cyclic CS Mild forms of hypercortisolism |
| Metanephrines | Drugs Amphetamines Buspirone Decongestants Ethanol Levodopa Prochlorperazine SNRIs TCAs Withdrawal from clonidine Acute illness and/or hospitalization Autonomic dysfunction Hemodialysis (plasma) |
Reduced renal filtration (urine) |
| Plasma Renin Activity | Direct renin inhibitors | ACEi/ARB Diuretics Mineralocorticoid receptor antagonists Pregnancy Sodium restriction |
| Aldosterone | Hyperkalemia | Hypokalemia |