A 44-year-old man with no medical history walked into a Chinese hospital with a low-grade fever, poor appetite, nausea, and an aching lower back. Blood drawn that day showed a serum creatinine of 393 micromoles per liter. The next morning, it had climbed to 540, against a laboratory reference range that topped out at 97. His kidneys were failing fast, and nobody could say why.
The answer turned out to be a jar of homemade liquor with star fruit steeping in it.
The case was published in Frontiers in Medicine by a team at Deqing People's Hospital in Zhejiang. The authors describe it as a rare instance of oxalate nephropathy following star fruit-infused liquor, a preparation they say is seldom reported, even though star fruit itself is a known kidney hazard.
The Clue Doctors Missed Until They Asked a Third Time
The initial workup was exhaustive and almost entirely unhelpful. Tests for streptococcal antibodies, inflammatory markers, hepatitis B, antinuclear antibodies, anti-glomerular basement membrane antibodies and vasculitis-associated nephritis all came back negative. Electrocardiography, renal vascular ultrasound and abdominal computed tomography found nothing.
What the laboratory did show was tubular injury, so the team suspected acute interstitial nephritis and started intravenous methylprednisolone alongside fluids and urine alkalinization. Creatinine dipped to 473, then stalled.
Only on repeated questioning did the patient mention the liquor. He had steeped roughly four star fruits per 500 grams of white liquor for about a month. Four days before admission, he drank around 500 milliliters of it, and symptoms started the next day. He denied eating other high-oxalate foods such as nuts or spinach.
Star fruit, or carambola, is rich in oxalate. A narrative review of star fruit toxicity and a case series from Sri Lanka have both documented acute kidney injury after heavy ingestion. In that series of four men, nausea, vomiting, and abdominal and back pain came first, followed by falling urine output and rising creatinine over hours to days. The sour variety carries far more oxalate than the sweet one.
Crystals in the Tubules, Visible Only Under Polarized Light
A percutaneous kidney biopsy settled it. Under light microscopy, the glomeruli looked only mildly altered, but the tubules showed moderate injury, with degeneration of the lining cells and loss of the brush border. Under polarized light, birefringent crystals glittered inside some tubular lumens, consistent with focal calcium oxalate deposition. Electron microscopy revealed swollen mitochondria and loss of the microvilli lining healthy tubular cells.
Interstitial inflammation was mild and focal, involving roughly 2 percent of the sampled cortical area, which the authors say does not support prolonged immunosuppression. Because steroids were started empirically before the biopsy result returned, the team acknowledges it cannot separate how much of his early improvement came from the drug and how much came from fluids and stopping the exposure.
When the oxalate load exceeds what the kidneys can excrete, oxalate binds to calcium and forms crystals that obstruct the tubules and injure the cells lining them. The mechanism is well described in the oxalate nephropathy literature, and a report of oxalate nephropathy after yellow rice wine suggests infused alcoholic drinks are an underappreciated route.
Getting there required ruling out the usual suspects one by one. Toxic nephropathy was unlikely because he denied any medication or unknown exposure. Acute tubular necrosis typically follows ischemia or a toxin and shows characteristic casts in the urine. Uric acid nephropathy produces crystals that bend polarized light in the opposite direction and is usually associated with gout or hyperuricemia. Blood gas analysis showed metabolic acidosis (pH 7.31), and a urine panel flagged elevated beta-2 microglobulin, both pointing to the tubules rather than the filtering units.
Most secondary oxalate nephropathy does not look like this. The authors note that gut-related causes, such as chronic pancreatitis or previous gastrointestinal surgery, account for roughly 60 percent of cases, while excessive intake of oxalate-rich foods or their precursors accounts for about 23 percent. This patient had no digestive history, placing him squarely in the dietary category.
Fourteen Months Later, His Kidneys Have Not Fully Recovered
He went home eight days after admission with creatinine down to 293. Steroids were tapered and stopped in late May 2025, and days later his creatinine measured 142, still above normal.
At his most recent recorded follow-up, in June 2026, it was 121.11. More than a year on, his kidney function had never returned to baseline, and the authors conclude that his acute kidney injury progressed to chronic kidney disease. He was previously healthy; he was treated aggressively, and he still lost function permanently.
Several caveats apply. This is a single patient. Urinary and serum oxalate were never quantified because those assays were not part of the hospital's routine menu; therefore, the systemic oxalate burden is unknown. Follow-up data beyond creatinine could not be obtained, so the report cannot stage his chronic kidney disease. The authors also speculate that heavy drinking worsened the injury, which is plausible but unproven.
Nothing here suggests that eating star fruit normally causes kidney failure. This was a concentrated exposure in one large dose. People with existing kidney disease are already advised to avoid star fruit, and anyone with unexplained nausea, back pain, and reduced urine output after an unusual ingestion should be evaluated promptly.
Key Questions Answered
What caused the kidney injury?
A biopsy showed calcium oxalate crystals in the tubules. The team traced the oxalate to about 500 milliliters of homemade liquor in which star fruit had steeped for roughly a month.
Does eating star fruit normally damage the kidneys?
No. This involved a concentrated infusion taken in a single sitting. Reported injuries generally follow heavy ingestion, and the sour variety carries more oxalate than the sweet one.
Who is most at risk?
People with existing kidney disease are the established high-risk group and are advised to avoid star fruit. This patient had no prior kidney problems, which is what makes the case notable.
What symptoms appeared first?
Low-grade fever, poor appetite, nausea, and lower back soreness, starting the day after he drank the liquor. The case series reports similar symptoms plus vomiting and decreased urine output.
Did he recover?
Partially. His creatinine fell from a peak of 540 to 121.11 at the latest follow-up, though it remains above normal. The authors report progression from acute kidney injury to chronic kidney disease.
How reliable is a single case report?
It documents that something can happen, not how often. Urinary oxalate was never measured, and steroids were given before diagnosis, limiting conclusions about treatment.
