What Is the Kasai Procedure for Biliary Atresia?

The Kasai procedure, formally called hepatic portoenterostomy, is an operation that reroutes bile flow in infants born with biliary atresia, a condition in which the bile ducts outside and inside the liver are blocked or absent. First performed in 1950 by Japanese surgeon Morio Kasai, the operation was the first effective treatment for a disease that had previously been a death sentence within months.¹ Today it remains the first-line surgical treatment, though it is palliative rather than curative, and a significant number of children who undergo it will eventually need a liver transplant.

What Biliary Atresia Is and Why Surgery Is Urgent

Biliary atresia is a progressive disease that destroys the bile ducts, causing bile to back up into the liver. That backup leads to jaundice in newborns and, if untreated, rapid liver scarring and failure. The exact cause remains unclear, but researchers believe multiple factors converge: a viral infection around the time of birth may damage the cells lining the bile ducts, triggering an immune response that causes further inflammation and scarring.² Genetic susceptibility and problems with how the bile ducts form before birth have also been implicated.³ None of these factors alone fully explains the disease, which is part of why biliary atresia can be frustratingly hard to diagnose quickly.

Biliary atresia is the leading reason children under two receive liver transplants, accounting for up to three quarters of those procedures.⁴ The Kasai procedure exists to delay or prevent that transplant by restoring some bile drainage before the liver is too damaged.

How the Surgery Works

The surgeon removes the damaged, obstructed bile ducts outside the liver and exposes a flat surface at the base of the liver called the porta hepatis, where tiny remnant bile ductules may still be open. A loop of the baby’s own small intestine is then brought up and stitched directly to that surface, creating a new pathway for bile to drain from the liver into the gut. The concept is deceptively simple: if microscopic bile channels at the liver’s surface are still open, bile can trickle into the attached intestinal loop and eventually reach the digestive tract. Success depends heavily on how many of those tiny channels remain functional at the time of surgery, which is why timing is critical.

Why Age at Surgery Matters So Much

The liver damage in biliary atresia is progressive, so every day of bile backup destroys more tissue. In a large U.S. database analysis, the median age at Kasai surgery was 57 days, with most babies operated on between about 41 and 71 days of life.⁵ The general consensus is that surgery performed before 60 days of age gives the best chance of restoring bile flow, though there is real institutional variation. A multi-center study found that the time from starting the diagnostic workup to actually performing the operation varied enormously between hospitals, with delays up to nearly 25 days at some centers. Those differences in institutional speed affected the odds of a baby’s bilirubin normalizing by three months.⁶

That said, older age is not an absolute barrier. Even in babies older than 90 days, the Kasai procedure can prolong native-liver survival and serve as an important bridge to transplant.⁷ The operation is generally still offered to late-presenting infants because even partial success buys time, and time matters when the alternative is joining a transplant waiting list as a very small infant.

Stool Color Screening and Early Detection

One of the most practical tools for catching biliary atresia earlier is surprisingly low-tech: a stool color card given to new parents. Normal infant stool gets its yellow-green color from bile pigments, so pale or clay-colored stools are a red flag for blocked bile flow. Taiwan pioneered a national stool color card screening program, and the results were striking. After the program launched, the median age at Kasai surgery dropped from 51 to 48 days, and the share of operations performed within the first 60 days of life rose from about 69% to 74%.⁸ The screening program also increased the rate at which babies were jaundice-free three months after surgery.⁹ Japan has seen similar benefits. The card costs almost nothing to produce and distribute, making it one of the few screening tools that works well even in countries with limited healthcare budgets.

Post-Operative Medications

After the Kasai procedure, most centers give some combination of steroids, a bile acid called ursodeoxycholic acid (commonly shortened to UDCA), and antibiotics. The rationale for each differs, and the evidence supporting them varies in strength.

Steroids

Steroids are meant to reduce the inflammation around the remaining bile ductules and improve bile drainage. A study comparing high-dose and low-dose steroid regimens found meaningfully different results: roughly 53% of babies on the high-dose protocol were jaundice-free at three months, compared with about 39% in the low-dose group. The high-dose group also had better two-year native-liver survival, at about 54% versus 43%.¹⁰ Babies receiving steroids around the time of surgery also had shorter hospital stays, averaging about three and a half fewer days than those who did not.¹¹ Despite these encouraging findings, steroid protocols still vary between centers because the ideal dose and duration have not been settled by large randomized trials.

Ursodeoxycholic Acid

UDCA is a naturally occurring bile acid that makes up only a small fraction of the total bile acid pool in humans. After the Kasai, it is thought to help by displacing more toxic bile acids that damage liver cells and by calming the immune activity around the bile ducts. Research has shown that its beneficial effects can persist for years after surgery, and it is now widely prescribed as a long-term medication for children who have good bile flow after the Kasai.¹²

Prophylactic Antibiotics

Because the Kasai creates a direct connection between the intestine and the liver, bacteria from the gut can travel up into the bile ducts and cause infection, a complication called cholangitis. Many surgeons prescribe long courses of antibiotics hoping to prevent this. However, the evidence here is disappointing. A meta-analysis pooling data from multiple studies found that prophylactic antibiotics did not significantly reduce the incidence of cholangitis after the Kasai procedure.¹³ A randomized trial comparing short-term and long-term intravenous antibiotics found no difference in the overall rate of cholangitis within six months, though longer courses did modestly reduce early-onset episodes and the total number of infection episodes.¹⁴ A separate retrospective study found that shorter antibiotic courses resulted in significantly shorter hospital stays with no difference in cholangitis incidence.¹⁵ The bottom line is that the practice continues partly out of habit, but the data do not strongly support prolonged antibiotic prophylaxis.

Laparoscopic Versus Open Surgery

Over the past two decades, some centers have tried performing the Kasai through small incisions using a camera and specialized instruments, the laparoscopic approach. In theory, this could mean less pain, a smaller scar, and faster recovery for the baby. In practice, outcomes have been mixed and somewhat sobering. A randomized trial with follow-up extending beyond ten years found that the six-month jaundice-free rate was roughly 53% for laparoscopic Kasai and 61% for the open approach, a gap that was not statistically significant. But the ten-year native-liver survival trended lower in the laparoscopic group, at about 44% versus 59%.¹⁶ A Japanese multicenter study found no significant difference in short-term outcomes between the two approaches.¹⁷ Another small study observed five-year native-liver survival of 50% in the laparoscopic group versus 81% in the open group, though the sample was too small to reach statistical significance.¹⁸

The concern is that the laparoscopic approach may not allow the surgeon to expose enough of the porta hepatis surface area, which could limit the number of tiny bile ductules that get connected. Most high-volume centers have either returned to the open technique or reserve laparoscopy for selected cases. The open Kasai remains the standard.

Long-Term Complications Even After Successful Surgery

A successful Kasai, defined as one that restores bile flow and clears jaundice, does not mean the liver is healthy. Roughly 30 to 40% of long-term survivors who keep their native liver develop complications such as recurrent cholangitis and portal hypertension, a condition where pressure builds in the blood vessels supplying the liver.¹⁹ Portal hypertension can lead to enlarged veins in the esophagus (varices) that carry a risk of serious bleeding. Recent research has identified serum bile acid levels as an early biomarker that can predict which children will develop portal hypertension and high-risk varices within five years of a successful Kasai.²⁰

For children who develop severe portal hypertension but still have reasonable liver function, surgical shunts can relieve the pressure and delay or avoid transplant. In one long-term study, children who received shunts at a median age of about five and a half years had ten-year overall survival of 87% and ten-year transplant-free survival of 70%. However, complications such as encephalopathy (confusion from toxins the liver can no longer clear) occurred in some patients, and many eventually needed transplant anyway.²¹

Nutritional Challenges After the Kasai

Even when bile flow is restored, children with biliary atresia often struggle to absorb fat and fat-soluble vitamins properly. A classic study found that deficiencies in vitamins A, D, and E were common in children after the Kasai, including those whose operations were considered successful. About 59% showed combined bone-thinning and softening from vitamin D deficiency.²² Children need ongoing monitoring of vitamin levels and supplementation, sometimes for years.

Formulas enriched with medium-chain triglycerides, a type of fat that does not require bile acids for absorption, can make a meaningful difference. In one study, babies fed these formulas along with nutritional counseling showed significant improvements in weight, arm measurements, and growth velocity within three to six months. Nearly 78% had low vitamin D levels at the initial assessment, but levels improved significantly with supplementation.²³ Adequate nutrition is not just a supportive measure; children who are better nourished tend to tolerate transplant surgery more successfully if it becomes necessary later.

The Role of Cytomegalovirus in Outcomes

Some babies with biliary atresia also have an active cytomegalovirus (CMV) infection at the time of diagnosis, and this appears to worsen their long-term prognosis. A study analyzing the impact of CMV found that it was an independent risk factor for native-liver failure after the Kasai, roughly doubling the hazard of losing the native liver. Interestingly, CMV did not significantly affect the short-term success rate of the surgery itself, but the cumulative rate of native-liver failure over time was significantly higher in the CMV-positive group, and median native-liver survival was shorter.²⁴ Whether treating the CMV infection aggressively changes outcomes is still being studied, but it is another reason pediatric hepatologists pay close attention to viral serology in these babies.

When Transplant Becomes Necessary

The Kasai procedure does not cure biliary atresia. It buys time, sometimes years or even decades, but the underlying liver disease continues in most patients. One of the common questions families ask is whether a prior Kasai makes transplant harder when the time comes. A review of 57 transplant patients found that long-term survival after transplant was essentially identical whether or not the child had a prior Kasai, at about 74-75%. However, children who had undergone a Kasai first spent longer on the waiting list, averaging about 170 days compared with 63 days for those who went straight to transplant. The prior surgery can create abdominal adhesions that make the transplant operation more technically challenging.²⁵

Despite those trade-offs, the Kasai is still considered the right first step in almost all cases. The alternative, proceeding directly to transplant in a newborn, carries its own serious risks: infant transplant recipients face a lifetime of immunosuppressive drugs, the waiting list can be long, and donor organs for very small babies are scarce. By restoring some bile flow and keeping the native liver functional, even imperfectly, the Kasai gives the child time to grow, which improves transplant outcomes if a transplant eventually proves necessary.

Emerging Biomarkers for Monitoring

One of the challenges in managing children after the Kasai is figuring out early on which ones are going to do well and which are heading toward liver failure. Bilirubin levels are the traditional measure, but they give a relatively crude picture. A promising newer biomarker is a protein called MMP-7 (matrix metalloproteinase-7). A large multicenter study found that MMP-7 was extremely accurate at diagnosing biliary atresia in the first place, and that tracking MMP-7 levels after the Kasai could identify distinct patterns linked to prognosis. At six weeks after surgery, MMP-7 was the only significant predictor of whether a child would survive with their native liver at two years, and at three months post-surgery, it was the most accurate predictor among all tested biomarkers.²⁶ If validated widely, this blood test could help clinicians intervene earlier when the Kasai is failing, rather than waiting for jaundice or liver function to deteriorate on standard labs.

Quality of Life in Adulthood

One of the more encouraging parts of the biliary atresia story is what happens to people who make it to adulthood. A national cohort study of young adult biliary atresia survivors found that overall health-related quality of life was similar to that of age-matched peers, regardless of whether they had undergone transplant or were still living with their native liver.²⁷ That is a remarkable finding for a disease that was universally fatal before the Kasai procedure existed.

The picture is not uniformly rosy, though. Adults who kept their native liver scored lower on perceptions of their general physical health compared with transplanted patients and healthy controls. Active complications like cholangitis and portal hypertension were linked to lower vitality scores.²⁸ A Dutch study of native-liver survivors at a median age of 23 found that while their social functioning was actually better than that of the general population, their perceived general health was lower, and some individuals scored above clinical thresholds for anxiety and post-traumatic stress symptoms.²⁹ These findings suggest that even survivors who are doing well medically may benefit from psychological support, particularly women with native livers who seem to carry a higher burden of health-related worry.

The Kasai procedure was conceived in an era when its inventor was told that nothing could be done for these babies. Today it is the essential first intervention in a multi-step management pathway that can carry a child from infancy into independent adult life. Its limitations are real, but the operation’s existence transformed biliary atresia from a fatal disease into a chronic, manageable one.³⁰