Endocrine Abstracts

Published data has demonstrated that low 0900 h plasma total cortisol (PTC) immediately following traumatic brain injury (TBI) predicts mortality. However, potential discrepancies exist between PTC and plasma free cortisol (PFC). We hypothesised that low PTC would correlate closely with PFC and predict mortality and long-term hypopituitarism.

One hundred patients (84 men, median age 33, range 18–75) with TBI (mean GCS±S.D.=8.59±4.2) were recruited. Each had PTC and CBG, albumin, electrolytes, glucose, and urine osmolality measured on days 1, 3, 5, 7, and 10 following TBI. GCS and fluid balance were recorded daily. Results were compared with 15 controls admitted to ITU following major vascular surgery. A PTC <300 nmol/l in a patient in ITU was regarded clinically as inappropriately low. PFC was calculated for 25% of TBI samples and all control samples using Coolens’ equation¹. TBI patients reattended for dynamic pituitary testing (using the insulin tolerance test unless contraindicated) ≥6 months after TBI.

All controls had PTC >300 nmol, whereas 78/100 TBI patients had at least one PTC <300 nmol/l. TBI patients in the lowest quartile of PTC had the highest mortality (P=0.0187). PTC correlated closely with PFC in both TBI patients (r=0.99, P<0.0001) and controls (r=0.99, P<0.0001). 40/100 developed transient cranial diabetes insipidus (CDI) and 11/100 developed persistent CDI. When compared with those who did not develop CDI, mortality was significantly higher in those with persistent CDI (P=0.0003) and transient CDI (P=0.0002).

32/79 (40.5%) of TBI survivors attended for dynamic pituitary testing. The median time to testing was 14 months (range 6–24 months). 6/32 (18.8%) were ACTH deficient, 6/32 were GH deficient, and 1/32 (3.1%) was gonadotropin deficient. No patients were TSH or prolactin deficient. Lower mean PTC was associated with the development of chronic hypopituitarism (P=0.049).

Acute hypocortisolaemia and acute DI are common in TBI and predict mortality. PTC measurement correlates closely with plasma free cortisol estimate. Acute hypocortisolaemia may predict long term hypopituitarism.

1. Coolens JL, Van Baelen H & Heyns W. Clinical use of unbound plasma cortisol as calculated from total cortisol and corticosteroid-binding globulin. J Steroid Biochem. 1987 Feb;26 (2) 197–202.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.