Utility of blood tests in screening for metabolic disorders in kidney stone disease.

Katie S Eyre,Helen Cui,Sarah A Howles,Benjamin W Turney,Radu Mihai,Emily Grout,Francesca Lewis

doi:10.1111/bju.15250

Abstract

To determine the clinical utility of blood tests as a screening tool for metabolic abnormalities in patients with kidney stone disease. Clinical and biochemical data from 709 patients attending the Oxford University Hospitals NHS Foundation Trust for assessment and treatment of kidney stones were prospectively collected between April 2011 and February 2017. Data were analysed to determine the utility of serum calcium, parathyroid hormone (PTH), urate, chloride, bicarbonate, potassium and phosphate assays in screening for primary hyperparathyroidism, normocalcaemic hyperparathyroidism, hyperuricosuria, distal renal tubular acidosis (dRTA) and hypercalciuria. An elevated serum calcium level was detected in 2.3% of patients. Further investigations prompted by this finding resulted in a diagnosis of primary hyperparathyroidism in 0.2% of men and 4.6% of women for whom serum calcium was recorded. An elevated serum PTH level in the absence of hypercalcaemia was detected in 15.1% of patients. Of these patients, 74.6% were vitamin D-insufficient; no patients were diagnosed with normocalcaemic hyperparathyroidism. Hyperuricosuria was present in 21.6% of patients and hypercalciuria in 47.1%. Hyperuricaemia was not associated with hyperuricosuria, nor was hypophosphataemia associated with hypercalciuria. No patient was highlighted as being at risk of dRTA using serum chloride and bicarbonate as screening tests. This study indicates that individuals presenting with renal calculi should undergo metabolic screening with a serum calcium measurement alone. Use of additional blood tests to screen for metabolic disorders is not cost-effective and may provide false reassurance that metabolic abnormalities are not present. A full metabolic assessment with 24-h urine collection should be undertaken in recurrent stone formers and in those at high risk of future stone disease to identify potentially treatable metabolic abnormalities.

Highlights

Kidney stone disease is a common condition that affects up to ~20% of men and ~10% of women in their lifetime, accounts for over 85 000 hospital episodes each year in the UK, and was estimated to cost the US $3.79 bn in 2014 [1,2,3]
Whilst evidence exists for the use of allopurinol in patients with hyperuricosuria and normocalciuria to reduce kidney stone events [11,12,13,14], data demonstrating an association of hyperuricaemia alone with kidney stone formation is limited and the European Association of Urology (EAU) guidelines only advocate the use of xanthine oxidase inhibitors where hyperuricosuria exists [5,15,16]
We examined a large database of serum and urine biochemistries from individuals with kidney stone disease to ascertain the clinical utility of blood tests in screening for metabolic disorders in patients with nephrolithiasis

Summary

Introduction

Kidney stone disease is a common condition that affects up to ~20% of men and ~10% of women in their lifetime, accounts for over 85 000 hospital episodes each year in the UK, and was estimated to cost the US $3.79 bn in 2014 [1,2,3]. National and international guidelines recommend that patients presenting with kidney stones undergo metabolic screening with blood tests, with the aim of identifying cases that require further investigation to make a diagnosis such as this [5,6,7]. The NICE committee was unable to identify any evidence to inform recommendations for metabolic blood tests in patients with kidney stones, but made note of the high prevalence of primary hyperparathyroidism in these individuals and the low cost of serum calcium testing [6,8,9,10]. The AUA suggests that, as well as serum calcium and urate blood tests, serum chloride, bicarbonate and potassium are routinely measured as part of an assessment for dRTA [7]. Alterations in phosphate homeostasis may be linked to kidney stone formation and, a subset of clinicians will routinely assess serum phosphate levels in nephrolithiasis patients with the aim of identifying those with hypophosphataemia who may be at risk of hypercalciuria due to reduced phosphate levels stimulating 1,25(OH) vitamin D synthesis and enhancing intestinal calcium uptake [18,19]

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