The Industrial Injuries Advisory Council (IIAC) has published an information note on the occupational risks of recurrent kidney stones (urolithiasis)[i]. The note was published following an inquiry into a former seaman, who had served long periods in hot regions and developed urolithiasis. Currently, urolithiasis does not appear on the list of prescribed diseases for which disability benefit may be claimed.
Urolithiasis is the formation of stones anywhere in the upper urinary tract, including the bladder, the ureter or the kidneys. Stones most commonly originate in the kidneys, and often cause no symptoms. The stones may cause pain, known as ureteric colic, when they move from the kidney or obstruct the flow of urine. Sudden-onset, intense uretic colic is fairly common, and affects 1-2 people per 1000, every year. Around 12% of men and 6% of women will have one episode of ureteric colic at some stage in their life, and over 80% of stones are passed within a month without requiring treatment. In two-thirds of men, the stones can be recurrent. As the pain is usually intense, most people with stones seek medical attention. An individual could claim they were disabled by stones if they have caused significant damage to the kidneys or ureter, and perhaps if they had frequent recurrent episodes of ureteric colic.
There have been a few studies of occupational risks, which may cause stones to form. These studies are based on self-reported data. The incidence or prevalence of stones recorded may therefore be less reliable.
The Council did not find any published systematic reviews of occupational risk factors of urolithiasis, so it undertook its own review, and found the evidence to be limited. The review found that several occupational exposures have been described, but few associations have been replicated in other studies. The strongest evidence in support of occupationally induced urolithiasis is in those whose work entails exposure to renal toxins and in those who work in hot environments and suffer from dehydration. Although these groups showed the strongest evidence, the evidence could not be described as strong. The Council’s review focused on three areas: cadmium, other chemical exposures, and work at high ambient temperatures.
Cadmium is known to have toxic effects on kidney function. Two Swedish studies have reported that the risk of kidney stones increases with increasing exposure to cadmium: a study of soldiers found that prevalence of stones was highest in those with the highest levels of blood cadmium[ii], and; a study of male employees at a battery factory found that incidence of stones was higher in those with highest estimated cumulative exposure to cadmium[iii]. Similarly, a study from Glasgow found that the prevalence of stones in coppersmiths exposed to cadmium was 40%, compared to 3.5% in an unexposed population[iv].
Chemical exposure was also identified as potentially increasing the risk of kidney stones. 18% of workers in a plastics factory, exposed to trimethyltin, a chemical used in the manufacture of PVC, developed kidney stones, compared to 6% in another factory where there had been exposure[v]. The prevalence of renal colic in Norwegian workers exposed to oxalic acid, which was used to clean railway carriages before repainting, was 53%, compared to 12% in co-workers who were not exposed[vi]. It is also possible that exposure to ethylene glycol may cause changes in urinary chemistry that could lead to the formation of kidney stones[vii], but the incidence in exposed workers has not been studied.
A few studies of work in hot conditions have provided useful estimates. A study of Brazilian steel industry workers found that the prevalence of kidney stones was 8% in those working in temperatures hotter than 45°C, compared with 1% among other workers[viii]. In a study of machinists in an Italian glass factory, the prevalence of kidney stones was 8.5%, compared to 2.4% in employees working at normal temperatures. In workers exposed to heat stress, the prevalence of stones was 39%[ix]. A study from Glasgow compared kidney stone patients with the local population, and found that 67% of patients had occupational exposure to hot metals, compared to 26% of the local population[x]. In Singapore, a study found that the prevalence of kidney stones was 5 times higher in outdoor workers than in indoor workers, with 5.2% versus 0.85% of workers affected[xi].
The Council only found one study relevant to seamen, published in 1965. In a study of 350 Royal Navy personnel with confirmed urolithiasis, between 1958 and 1964, the estimated prevalence among non-officers was highest in engineers and cooks, which are the two occupations in which workers are exposed to the highest temperatures. In respect of all personnel, the rates were highest in those who had served in the Middle East or Far East[xii].
The Council concluded that both working with renal toxins and working in a hot, dehydrating environment probably increases the risk of urolithiasis. However, this assumption is based on a small pool of evidence, which lacks quality. Thus, the Council concluded that there was insufficient evidence to recommend that urolithiasis should be added to the list of prescribed diseases.
[i] Occupational risks for urolithiasis: IIAC information note. Industrial Injuries Advisory Council. 26 April 2018. https://www.gov.uk/government/publications/occupational-risks-for-urolithiasis-iiac-information-note/occupational-risks-for-urolithiasis-iiac-information-note (Accessed 2 May 2018)
[ii] Jarup L, Persson B, Elinder CG. Blood cadmium as an indicator of dose in a long-term follow-up of workers previously exposed to cadmium. Scandinavian journal of work, environment & health. 1997;23(1):31-6 http://www.jstor.org/stable/40966600?seq=1#page_scan_tab_contents (Accessed 3 May 2018)
[iii] Jarup L, Elinder CG. Incidence of renal stones among cadmium exposed battery workers. British journal of industrial medicine. 1993;50(7):598-602 http://www.jstor.org/stable/40966600?seq=1#page_scan_tab_contents (Accessed 3 May 2018)
[iv] Scott R, Cunningham C, McLelland A, Fell GS, Fitzgerald-Finch OP, McKellar N. The importance of cadmium as a factor in calcified upper urinary tract stone disease–a prospective 7-year study. Br J Urol. 1982;54(6):584-9 https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1464-410X.1982.tb13601.x (Accessed 3 May 2018)
[v] Tang X, Li N, Kang L, Dubois AM, Gong Z, Wu B, et al. Chronic low level trimethyltin exposure and the risk of developing nephrolithiasis. Occupational and environmental medicine. 2013;70(8):561-7 https://www.researchgate.net/profile/Xiaojiang_Tang/publication/259449076_Evidences_for_B6C3-Tg_APPswePSEN1dE9_Double-Transgenic_Mice_Between_3_and_10_Months_as_an_Age-Related_Alzheimer%27s_Disease_Model/links/02e7e53619ce0ac25a000000.pdf (Accessed 3 May 2018)
[vi] Laerum E, Aarseth S. Urolithiasis in railroad shopmen in relation to oxalic acid exposure at work. Scandinavian journal of work, environment & health. 1985;11(2):97-100 http://www.jstor.org/stable/40965192?seq=1#page_scan_tab_contents (Accessed 3 May 2018)
[vii] Laitinen J, Liesivuori J, Savolainen H. Urinary alkoxyacetic acids and renal effects of exposure to ethylene glycol ethers. Occupational and environmental medicine. 1996;53(9):595-600 http://oem.bmj.com/content/oemed/53/9/595.full.pdf (Accessed 3 May 2018)
[viii] Atan L, Andreoni C, Ortiz V, Silva EK, Pitta R, Atan F, et al. High kidney stone risk in men working in steel industry at hot temperatures. Urology. 2005;65(5):858-61 https://s3.amazonaws.com/academia.edu.documents/45873381/j.urology.2004.11.04820160523-12370-637zg0.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1525328126&Signature=QIsN6Axr%2B3rujGZzJ2czfF69a%2BE%3D&response-content-disposition=inline%3B%20filename%3DHigh_kidney_stone_risk_in_men_working_in.pdf (Accessed 3 May 2018)
[ix] Borghi L, Meschi T, Amato F, Novarini A, Romanelli A, Cigala F. Hot occupation and nephrolithiasis. J Urol. 1993;150(6):1757-60 https://www.jurology.com/article/S0022-5347(17)35887-1/abstract (Accessed 3 May 2018)
[x] Ferrie BG, Scott R. Occupation and urinary tract stone disease. Urology. 1984;24(5):443-5.. https://www.goldjournal.net/article/0090-4295(84)90318-2/abstract (Accessed 3 May 2018)
[xi] Pin NT, Ling NY, Siang LH. Dehydration from outdoor work and urinary stones in a tropical environment. Occupational medicine (Oxford, England). 1992;42(1):30-2 https://academic.oup.com/occmed/article-abstract/42/1/30/1358274 (Accessed 3 May 2018)