By Prof Ram Shankar Upadhayaya
Elevated blood glucose levels characterize diabetes, but it’s essential to distinguish between two types of glucose measurements – serum and blood glucose. Serum glucose levels are typically 10-15% higher than blood glucose.
This difference arises because serum measurements are taken from blood samples that have had blood cells removed, which can affect the relative values of glucose. This is the first concept to understand when considering serum or blood glucose levels.
The second concept pertains to the role of the kidneys in managing glucose. Usually, kidneys filter fluids, and the filtrate contains minerals such as potassium, magnesium, calcium, and trace amounts of proteins, including glucose.
In a healthy person, nearly all the minerals and glucose are reabsorbed into the bloodstream. However, in individuals with diabetes, especially when blood glucose levels are high, the glucose transporters in the kidneys can become overwhelmed. When this happens, excess glucose remains in the urine instead of being reabsorbed. The healthy threshold for glucose is typically around 160 milligrams per deciliter of filtrate. Any glucose greater than the healthy threshold will start appearing in the urine.
When glucose is present in the urine, it exerts an osmotic effect, attracting water, sodium, potassium, and other electrolytes. This can result in excessive thirst and frequent urination, known as polydipsia and polyuria.
However, glycosuria (glucose in the urine) does not automatically indicate diabetes. In some situations, glucose appears in the urine, but the individual does not have diabetes. A few examples of such conditions are genetic abnormalities involving the SGLT2 gene, in which sodium glucose pumps are abnormal and do not do well even at healthy glucose levels, leading to glycosuria without diabetes.
Similarly, Fanconi Syndrome is a chronic renal disease in which glucose transporters and reabsorption functions will be affected. In chronic renal disease, glucose, potassium, magnesium, calcium, and proteins are not reabsorbed. So, all of those ionic levels will go down in the blood, and cause related issues. During pregnancy, the glomerular filtration rate (GFR) in the kidneys increases. This enhanced filtration can result in glucose appearing in the urine. However, the presence of glucose in urine during pregnancy does not necessarily indicate diabetes. In such cases, blood glucose tests are typically more reliable for diagnosing diabetes.
In individuals with diabetes, the presence of ketones in the blood and urine can occur due to insufficient insulin, which prevents glucose from entering cells for energy. This situation prompts the body to rely on alternative energy sources, such as liver fat breakdown (lipolysis) and gluconeogenesis, leading to the production of ketones, including acetoacetic acid and beta-hydroxybutyric acid.
Ketones are acidic substances and can lead to diabetic ketoacidosis (DKA) which is characterized by dehydration, acetone breath (a fruity odor on the breath), dry mouth, and extreme thirst. Ketones increase in the blood and urine, contributing to osmotic diuresis, leading to excessive urination and further dehydration.
Moreover, ketones can behave like glucose in the body, and their increased presence in the blood can lead to other complications. They can cause a drop in potassium, magnesium, calcium, and phosphate levels in the blood, resulting in electrolyte imbalances.
Ketones are acidic, contribute to metabolic acidosis, and bind with blood proteins. One essential blood protein affected by this binding is albumin, which has various roles in the body, such as transporting substances. When ketones attach to albumin, they impair normal function, disrupting the body’s processes. This disruption can lead to symptoms like confusion, disorientation, and unconsciousness.
As a response to metabolic acidosis, individuals with DKA may hyperventilate to remove excess carbon dioxide from the body, attempting to compensate for the acidosis. This compensatory hyperventilation can lead to symptoms such as frequent urination, excessive thirst, dehydration, confusion, and disorientation.
Clinically, when a patient’s ketone level reaches 0.6 millimoles per litre or higher, it warrants further investigation to understand the situation. However, if the levels exceed three millimoles per litre, admitting the patient to the hospital becomes necessary. In Type 2 diabetes patients, diabetic ketoacidosis (DKA) can develop due to factors such as incorrect insulin administration, using the wrong insulin injection pen, or dietary habits.
Understanding the relationship between glucose, serum, blood levels, glycosuria, and ketones is crucial in managing and diagnosing diabetes and related complications, such as DKA. The presence of glucose in the urine, though often associated with diabetes, may not always indicate the condition. A thorough evaluation is necessary to differentiate between various underlying causes. Additionally, recognizing the consequences of ketone buildup and metabolic acidosis is vital for early intervention and appropriate medical care in diabetics.
(The writer is a US-based medical scientist)
