All About Lactose Intolerance and Lab Testing

Lactose is a type of sugar found in mammal milk. Lactose intolerance is a condition where the ability of the body to digest lactose is reduced. Lactose is present in breast milk, yogurt, cheese, butter, and ice cream. Individuals who are lactose intolerant might develop certain abdominal symptoms within 30 minutes to 2 hours of consuming dairy products. The severity of symptoms may vary from individual to individual and depends on the type and amount of dairy products consumed.  

Lactose is a sugar that has a complex structure known as a disaccharide. Before lactose could be absorbed and used by the body, it needs to be broken down into simple sugars such as glucose and galactose – both monosaccharides. This digestion process is initiated by lactase – an enzyme that’s produced in the cell linings of the small intestine. If a person doesn’t produce enough lactase, the undigested lactose is passed through the small intestine into the large intestine. Bacteria in the large intestine will break down the lactose, producing excess lactic acid and hydrogen and, thus, inhibiting water and salt absorption.  This can result in abdominal cramps and diarrhea. 

The lactase enzyme is produced in developing babies during pregnancy and peaks near birth. Most all babies are able to digest milk though some premature infants may have some intolerance.  Normal production of lactase track’s an infant’s milk consumption as breast milk is the primary source of nutrition. The lactase levels in babies decrease after the first couple of years and continue to decrease with age.  But 35% of adults across the world can produce lactase throughout adulthood and could digest lactose with no symptoms. This condition is known as lactase persistence or LP and is common to specific ethnicities and races. Northern European people have the highest rate of LP and the lowest incidence of lactose intolerance. Native American and Asian adults have the highest incidence of lactose intolerance. 

Ethnic Group                % Of Lactose Intolerance in Adults 

Southeast Asians         98% 

Indian Adults                50% 

Asian Americans          90% 

African Americans      79% 

Mexican Americans     55% 

Northern Europeans   05% 

Types of Lactose Intolerance 

There are a number of other conditions and diseases that can cause a secondary form of lactose intolerance in addition to the natural intolerance associated with increasing age. Damage to the lining of the small intestines can lead to the inability to absorb lactose in a beneficial manner. Radiation therapy, celiac disease, inflammatory bowel disease (or IBS), chemotherapy, overgrowth of bacteria or infections caused by parasites, all may result in a decreased lactose digestion.  Stomach contents in the small intestines move much quicker than normal in some people. These people can suffer from the condition because of insufficient time to digest lactose. Lactase deficiency is grouped into three clinical syndromes – alactasia (or congenital lactase deficiency), hypolactasia (or primary adult lactase deficiency), and secondary lactase deficiency. 

Congenital Lactase Deficiency 

There are two genes linked to the production of the lactase enzyme. The LCT gene is responsible for the production of lactase, and the MCM6 gene is responsible for controlling the expression of the LCT gene. Mutations to the LCT gene may result in congenital lactase deficiency. It’s an autosomal inheritance that requires one mutated gene from each parent. Congenital lactase deficiency is a rare form of lactose intolerance that begins at birth. It may severely inhibit the baby’s ability to digest milk and milk-based formulas. 

Primary Adult Lactase Deficiency 

Primary adult lactase deficiency is a common form of lactose intolerance. It is linked to the decreased production of lactase in adults. The affected individual will be less likely to suitably digest lactose due to this condition. The intensity of the condition may vary depending on the ethnic and racial makeup. The MCM6 gene regulates the functions of the LCT gene. This will result in a decrease in lactase production over time (or nonpersistence). Northern European people, primarily, have an inherited MCM6 gene mutation that could lead to persistence in digesting lactose in adulthood.  People who don’t have this mutation will lose the ability to produce lactase as they grow old that may result in lactose intolerance in the long run.  

Secondary Lactose Intolerance 

The symptoms of lactose intolerance are also prevalent in other gastrointestinal conditions, usually caused by a disease or damage to the lining of the small intestine.  This can lead to the loss of lactase.  Your healthcare provider can perform certain tests to determine the various conditions that have similar symptoms.  Different conditions have different prognoses and treatments. Treating the primary condition can reverse the secondary lactose intolerance condition.

Here are some other conditions that have similar symptoms: 

  • Crohn’s disease 
  • Celiac sprue 
  • Whipple disease 
  • Bacterial growth syndrome 
  • Short bowel syndrome 
  • AIDS 
  • Tropical sprue 
  • Giardia infections 
  • Cystic fibrosis 
  • Radiation or chemotherapy 
  • Zollinger Ellison syndrome 

Symptoms of Lactose Intolerance

The symptoms of lactose intolerance occur primarily due to undigested lactose reaching the large intestines. Extra fluids will be drawn into the large intestines where bacteria will break down the lactose. It will result in the excess production of hydrogen gas and lactic acid. This may cause: 

  • Abdominal bloating 
  • Abdominal cramps and pain 
  • Nausea 
  • Diarrhea 
  • Flatulence and excessive gas 

The severity of symptoms will vary depending on the individual and the amount and type of dairy products ingested. Many people who suffer from the condition can successfully consume small amounts of dairy products with few or no symptoms at all.  Some people confuse lactose intolerance with an allergy to cow’s milk.  Milk allergy happens due to a reaction by the immune system. The allergy is directed against a protein in the milk but not sugar.  A person who has a milk allergy can suffer mild to severe symptoms, and even life-threatening reactions, within minutes to hours soon after consuming cow’s milk.  They can also experience hives and wheezing in addition to the other symptoms associated with the allergy.  Lactose intolerance affects more adults than children.  On the contrary, milk allergies are much more common in young kids who tend to outgrow the allergy with aging.  

Laboratory Tests for Lactose Intolerance 

The goal of lab tests for lactose intolerance is to diagnose the condition and distinguish it from other conditions with similar symptoms.

  • Hydrogen breath test – This is the most effective lab test to diagnose lactose intolerance at this time.  Breath samples of the patient are taken before (as the baseline) and at times after the person drinks a fluid with lactose.  Hydrogen is produced in excess in the large intestines in a person who suffers from lactose intolerance.  This hydrogen moves to the circulation system and eventually is exhaled by the lungs.  Increased levels of hydrogen in the breath over time is a strong indicator of a lactose intolerance condition.  Lactose tolerance blood test – Blood samples are tested for glucose at different times – once an oral dose of lactose is given to the person. If the glucose level in the blood doesn’t rise, lactose intolerance may be present.  This test is rarely ordered in a clinical environment. 
  • Stool Acidity pH test – This test is usually performed on infants and kids who cannot undergo other tests.  Stools will become acidic when lactose intolerance is present.   

 Rarely ordered clinical tests for lactose intolerance include:

  • Genetic testing of the lactase or LCT gene 
  • Biopsy of a sample from the small intestine to diagnose lactase activity 

The aforementioned laboratory tests will be ordered by your health care provider to help diagnose whether you are suffering from lactose intolerance.