Mumbai’s searing heat leaves a distinct mark on blood and urine tests, study finds | Mumbai News
3 min readMumbaiJun 18, 2026 12:23 PM IST
Summer may be affecting the health of Mumbai residents differently from that of residents of many other Indian cities, according to an analysis of routine health check-up data by Plum Health Insurance.
The analysis, which compared health check-ups conducted during the summer months of April-May 2026 with those carried out during the winter period of November 2025-February 2026, found that Mumbai’s strongest summer signals were not the classic markers of dehydration seen in hot and dry regions.
Instead, patients in Mumbai were significantly more likely to have acidic urine, low iron levels, and lower haematocrit during summer. The share of patients with acidic urine rose by 32 per cent, low iron by 63 per cent and low haematocrit by 38 per cent compared to winter. At the same time, concentrated urine, a common indicator of dehydration, actually fell by 9 per cent. The analysis covered 1,382 patients from the Mumbai metropolitan region, including Thane and Navi Mumbai.
“Mumbai’s summer signal is more about acidic urine and blood markers such as iron and haematocrit than concentrated urine, consistent with humid-heat stress rather than classic dry dehydration,” the report noted.
The findings suggest that Mumbai’s coastal climate may produce a different physiological response to heat than the patterns typically observed in inland cities, where dehydration often manifests through increasingly concentrated urine.
The contrast was particularly evident in neighbouring Pune. Among 823 patients analysed, Pune was one of the few major metros where summer did not produce a clear dehydration signal. Concentrated urine levels were 22 per cent lower in summer than in winter, while low sodium levels fell by 50 per cent and low haematocrit by 28 per cent. Acidic urine remained largely unchanged.
“In one line: Pune does not follow the national summer-dehydration pattern — several markers are flat or lower in summer,” the report stated, adding that Pune should not be used as a “heatwave headline city”.
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Elsewhere, the analysis found stronger evidence of conventional dehydration patterns. Bengaluru, which had the largest dataset of 6,808 patients, showed increases across multiple urine and blood markers, including low sodium, acidic urine, concentrated urine and low haematocrit. Hyderabad recorded one of the strongest urine-concentration signals, with concentrated urine rising by 45 per cent and acidic urine by 88 per cent during summer. Delhi NCR also showed clear summer shifts, including a 28 per cent rise in concentrated urine and a 29 per cent increase in acidic urine.
Among coastal cities, Chennai displayed a mixed picture, with concentrated urine rising by 28 per cent and modest increases in low haemoglobin and low haematocrit, even as acidic urine declined.
The report noted that some smaller-city findings should be treated cautiously because of limited sample sizes. Jaipur, Ahmedabad, Indore and Kolkata each had fewer than 300 patients in the dataset. While Jaipur showed some of the largest increases in blood-marker abnormalities, the report described these as an early signal rather than definitive evidence.
Overall, the analysis suggests that summer’s health effects are not uniform across India. According to Plum, dry-heat cities tend to show stronger urine-concentration signals associated with dehydration, while humid coastal locations such as Mumbai may exhibit more pronounced changes in blood markers and urine acidity.
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