Overview
Cortisol binding globulin (CBG) low refers to a condition characterized by reduced binding capacity for cortisol, potentially leading to altered cortisol bioavailability and clinical manifestations akin to cortisol excess or deficiency, depending on the context 3.Diagnosis
Insufficient suppression of serum cortisol in overnight dexamethasone suppression test 3.
Elevated ACTH and cortisol levels with intact diurnal rhythm but at elevated baseline 3.
Increased circulating adrenal androgen levels 3.
Consider specific assays validated for the patient population (adult serum, urine, fetal/neonatal serum, amniotic fluid) to avoid assay-related errors 5.Management
Low-dose dexamethasone therapy (1-1.5 mg/day) shown to be clinically beneficial in some cases 3.
Monitor for side effects such as hypokalemia, especially with thiazide diuretics 3.
Tailor management based on clinical presentation (e.g., hormonal imbalances, metabolic effects) 3.Special Populations
Pregnancy and Neonates: Specific assay validation is crucial due to potential assay variability 5.
Comorbidities: Management should consider concurrent conditions like hypertension, which may require alternative therapies to thiazide diuretics 3.Key Recommendations
Utilize the overnight 1-mg dexamethasone suppression test to assess cortisol suppression, indicative of CBG deficiency 3 (Evidence: Moderate).
Consider low-dose dexamethasone therapy (1-1.5 mg/day) for symptomatic relief in patients with CBG deficiency 3 (Evidence: Weak).
Validate cortisol assays according to the patient's specific matrix (serum, urine, fetal/neonatal serum, amniotic fluid) to ensure accurate results 5 (Evidence: Strong).References
1 Anderson NL, De La Cruz SEW, Gaydos JK, Ziccardi MH, Harvey DJ. Effects of Season, Location, Species, and Sex on Hematologic and Plasma Biochemical Values and Body Mass in Free-ranging Grebes (. Journal of avian medicine and surgery 2021. link
2 Okamoto K, Liu G, Yu WG, Isohashi F. Immunochemical characterization of the ATP-stimulated glucocorticoid-receptor-translocation promoter from various organs of rat. Journal of biochemistry 1994. link
3 Lamberts SW, Koper JW, Biemond P, den Holder FH, de Jong FH. Cortisol receptor resistance: the variability of its clinical presentation and response to treatment. The Journal of clinical endocrinology and metabolism 1992. link
4 Carlone GM, Plikaytis BB, Arko RJ. Immune serum to protein molecular weight standards for calibrating Western blots. Analytical biochemistry 1986. link90229-0)
5 Murphy BE. Pitfalls in the assay of cortisol. Journal of immunoassay 1980. link