Stability of direct renin concentration and plasma renin activity in EDTA whole blood and plasma at ambient and refrigerated temperatures from 0 to 72 hours

OBJECTIVES

The aim of this study was to determine the appropriate transport and storage conditions for blood taken for direct renin concentration and plasma renin activity measurement, and whether cryoactivation of prorenin is seen at time points relevant to clinical practice.

METHODS

Blood was extracted from n=10 volunteers into K₂-EDTA tubes. Stability of renin was assessed in whole blood stored at room temperature (15-25 °C) and in the refrigerator (2-8 °C) at 0 h, 8 h, and 24 h. The stability of renin in plasma was determined under the same conditions at 0 h, 24 h and 72 h.

RESULTS

Stability of plasma renin activity and direct renin concentration in whole blood stored at room temperature was found to be acceptable for up to 24 h. At refrigerated temperature, whole blood stability was acceptable for measurement of direct renin concentration up to 8 h and plasma renin activity up to 24 h. In contrast, plasma renin activity was not stable in plasma stored at either room or refrigerated temperatures up to 24 h; however, direct renin concentration had acceptable stability in plasma stored at room temperature for up to 24 h, but stability was unacceptable at refrigerated temperatures.

CONCLUSIONS

Samples collected for plasma renin activity and direct renin concentration should be transported as whole blood to optimise stability. After sample processing, plasma can be kept at room temperature for up to 24 h for direct renin concentration, however, for determination of plasma renin activity separated plasma should be analysed or frozen as soon as possible.

Survey of renin and aldosterone testing practices by Ontario laboratories - Providing insight into best practices

Objectives

Testing for renin and aldosterone in clinical laboratories is complicated by pre-analytical considerations such as the posture for blood collection and susceptibility to cryoactivation of renin. From an analytical perspective, there are both renin activity and renin mass or concentration assays available. There can also be variability in result reporting practices and the aldosterone-renin ratio (ARR) cut-off applied to screen for primary aldosteronism (PA). The Institute for Quality Management in Healthcare (IQMH) Centre for Proficiency Testing surveyed laboratories on their handling of renin and aldosterone testing to better understand current practices.

Design and methods

An online survey was prepared and sent to 134 Canadian laboratories enrolled in endocrinology proficiency testing with IQMH.

Results

One hundred twenty Ontario laboratories submitted responses. While only six (5%) laboratories perform testing for both renin and aldosterone, 108 (90%) collect and process specimens to be tested by reference laboratories. The survey revealed considerable variation in practices including the recommended state of patients prior to sample collection (for example, regarding medications or salt intake), the patient posture specifications for sample collection, the precautions taken against cryoactivation of renin, the choice of renin activity or mass assay, and the ARR cut-off used. The available literature on these factors was then reviewed.

Conclusions

Although there is no standardized procedure for specimen collection, analysis, or result reporting for renin or aldosterone testing, we have attempted to summarize the available literature to develop evidence-based recommendations. Where laboratory practice differs from peers and/or recommended protocols, laboratories should review their practices.

Hypertension: The role of biochemistry in the diagnosis and management

Hypertension is defined as a persistently elevated blood pressure ≥140/90mmHg. It is an important treatable risk factor for cardiovascular disease, with a high prevalence in the general population. The most common cause, essential hypertension, is a widespread disease - however, secondary hypertension is under investigated and under diagnosed. Collectively, hypertension is referred to as a "silent killer" - frequently it displays no overt symptomatology. It is a leading risk factor for death and disability globally, with >40% of persons aged over 25 having hypertension. A vast spectrum of conditions result in hypertension spanning essential through resistant, to patients with an overt endocrine cause. A significant number of patients with hypertension have multiple cardiovascular risk factors at the time of presentation. Both routine and specialised biochemical investigations are paramount for the evaluation of these patients and their subsequent management. Biochemical testing serves to identify those hypertensive individuals who are at higher risk on the basis of evidence of dysglycaemia, dyslipidaemia, renal impairment, or target organ damage and to exclude identifiable causes of hypertension. The main target of biochemical testing is the identification of patients with a specific and treatable aetiology of hypertension. Information gleaned from biochemical investigation is used to risk stratify patients and tailor the type and intensity of subsequent management and treatment. We review the approach to the biochemical investigation of patients presenting with hypertension and propose a diagnostic algorithm for work-up.

Hyperaldosteronism: diagnosis, lateralization, and treatment

Primary hyperaldosteronism is an important and commonly unrecognized secondary cause of hypertension. This article provides an overview of the current literature with respect to screening, diagnosis, and lateralization. Selection and outcomes of medical and surgical treatment are discussed.

Monitoring of therapy in congenital adrenal hyperplasia

BACKGROUND

Congenital adrenal hyperplasia is a group of disorders caused by defects in the adrenal steroidogenic pathways. In its most common form, 21-hydroxylase deficiency, patients develop varying degrees of glucocorticoid and mineralocorticoid deficiency as well as androgen excess. Therapy is guided by monitoring clinical parameters as well as adrenal hormone and metabolite concentrations.

CONTENT

We review the evidence for clinical and biochemical parameters used in monitoring therapy for congenital adrenal hyperplasia. We discuss the utility of 24-h urine collections for pregnanetriol and 17-ketosteroids as well as serum measurements of 17-hydroxyprogesterone, androstenedione, and testosterone. In addition, we examine the added value of daily hormonal profiles obtained from salivary or blood-spot samples and discuss the limitations of the various assays.

SUMMARY

Clinical parameters such as growth velocity and bone age remain the gold standard for monitoring the adequacy of therapy in congenital adrenal hyperplasia. The use of 24-h urine collections for pregnanetriol and 17-ketosteroid may offer an integrated view of adrenal hormone production but target concentrations must be better defined. Random serum hormone measurements are of little value and fluctuate with time of day and timing relative to glucocorticoid administration. Assays of daily hormonal profiles from saliva or blood spots offer a more detailed assessment of therapeutic control, although salivary assays have variable quality.