Establishing Reference Intervals for Serum and Salivary Cortisol in a Selected Population in Kano, Nigeria.

OBJECTIVE: Serum cortisol has long been used in the assessment of disorders of the hypothalamic-pituitary-adrenal axis. The reference interval for cortisol in both serum and saliva depends on the analytical methodology and the population studied; hence, a locally derived population-based reference interval is recommended. To our knowledge, there are no studies on reference interval determination in the study area, raising concerns about the use of reference intervals established in European and North American populations. This work aimed to establish reference intervals for baseline serum and salivary cortisol levels among healthy adults in Kano, Nigeria, using methods available in our laboratory. METHODS: A cross-section of 148 apparently healthy reference individuals aged 16 to 67 years were recruited from a local community in Kano, Nigeria, using a systematic sampling technique. Baseline serum cortisol was analyzed using highly sensitive and specific electrochemiluminescence quantitative measurements on an automated immunology analyzer. Salivary cortisol levels were measured using Salimetrics' competitive enzyme-linked immunosorbent assay test kits. Parametric methods with a 95% confidence interval were used to calculate reference intervals. RESULTS: The reference intervals for cortisol in serum and saliva were 72.0 nmo/L to 554.0 nmol/L and 0.40 nmol/L to 18.0 nmol/L, respectively. There was a weak positive correlation between serum and salivary cortisol values, but this association was not statistically significant. CONCLUSION: The development of locally derived adult reference intervals can improve the diagnostic utility of serum and salivary cortisol assessment and strengthen the reliability of adrenal insufficiency diagnoses in our population.

Prevalence and Determinants of Endothelial Dysfunction among Adults Living with HIV in Northwest Nigeria.

Background: Endothelial dysfunction constitutes an early pathophysiological event in atherogenesis and cardiovascular disease. This study aimed to assess the prevalence, determinants, and degree of endothelial dysfunction in antiretroviral therapy (ART)-treated people living with HIV (PLWH) in northwestern Nigeria using brachial flow-mediated dilatation (FMD). Methods: This was a comparative, cross-sectional study. A total of 200 ART-treated adults living with HIV with no evidence of kidney disease were compared with 200 HIV-negative participants attending a tertiary hospital in Kano, Nigeria, between September 2020 and May 2021. Endothelial function was evaluated by measuring FMD with a high-resolution vascular ultrasound transducer. FMD was calculated as the ratio of the brachial artery diameter after reactive hyperemia to baseline diameter and expressed as a percentage of change. Blood and urine samples were obtained from participants in both arms. Urine albumin-to-creatinine ratio (uACR) was calculated using the 2021 CKD-EPI estimated glomerular filtration rate (eGFR) creatinine-cystatin C equation without the race variable, and low-density lipoprotein (LDL) cholesterol was measured using enzymatic method. Results: The overall mean age (± standard deviation) of the study participants was 42 ± 11 years. Participants in the comparison arm were younger than PLWH (38 ± 11 versus 46 ± 10 years, respectively). The median (interquartile range) uACR was 41.6 (23.2-162.9) mg/g for the ART-treated PLWH versus 14.5 (7.4-27.0) mg/g for healthy controls. PLWH had a significantly lower mean percent FMD when compared to HIV-negative participants (9.8% ± 5.4 versus 12.1% ± 9.2, respectively). Reduced FMD was independently associated with HIV infection (ß = -2.83%, 95% CI, -4.44% to -1.21%, p = 0.001), estimated glomerular filtration rate (ß = -0.04%, 95% CI, -0.07% to -0.01%, p = 0.004) and LDL cholesterol (ß = -1.12%, 95% CI, -2.13% to -0.11%, p = 0.029). Conclusion: HIV-positive status, lower estimated GFR, and higher LDL cholesterol levels were independently associated with endothelial dysfunction. Future prospective studies with larger cohorts of persons living with HIV (and age- and sex-matched HIV-negative controls) are needed to gain further insight into these important findings. In the interim, aggressive management of modifiable risk factors is warranted.