Generality
Normally, urine contains negligible traces of ketones; however, when their blood concentration increases, the body tries to get rid of the excess of ketones by eliminating them with urine, where they increase significantly in quantity.
Ketonuria gives the urine a characteristic chloroform odor.
Ketones: What they are
From the metabolic stages specified below, the ketone bodies originate, alternative fuels to glucose but not exactly "ecological". The accumulation of these substances in the blood (ketosis), in fact, decreases their pH up to cause:
- Fatigue;
- General malaise;
- Emission of large amounts of urine;
- Intense thirst;
- Dehydration;
- cramps;
- Cardiac arrhythmias;
- Short and frequent breath;
- Drowsiness;
- Weight loss.
From the oxidation of glucose in the Krebs cycle, a substance is produced - oxalacetate - which combines with the acetyl-CoA deriving from the Β-oxidation of free fatty acids; from this union originates the citrate, which undergoes the Krebs reaction cycle for further oxidation up to carbon dioxide and water.
If the availability of oxalacetate is low (reduced intracellular glucose availability) in the face of high concentrations of acetyl-CoA (marked fatty acid catabolism), two moles of acetyl-CoA are combined to form acetoacetyl-CoA, a precursor of acetoacetate (a ketonic body), which in turn can originate 3-hydroxybutyrate and acetone (the other two ketone bodies).
Why do you measure
Ketones are an intermediate product of fat metabolism that originates when:
- The individual does not eat enough carbohydrates (in the event of loss of appetite or high protein diet);
- The body is not able to use carbohydrates properly.
When carbohydrates are not available, the body metabolizes fatty acids in order to obtain useful energy for sustenance.
The appearance of ketone bodies (acetacycetic acid, beta-hydroxybutyric acid and acetone) in the urine coincides with the increase of these substances in the blood ( ketonemia ), a condition that occurs when the tissues' ability to rapidly metabolize ketone bodies is reduced.
Urine ketones can give an early indication of insulin deficiency in a person with diabetes. Intense physical exercise, exposure to cold and loss of carbohydrates, which occurs, for example, with frequent vomiting, can increase fat metabolism, leading to ketonuria.
The analysis of ketone bodies is an extremely important test to verify if the organism is having some problems in using insulin. For this reason, the examination is recommended for diabetic subjects under insulin treatment.
Normal values
Normally, the amount of ketone bodies in the urine is very low, so much so that it cannot be measured with the usual techniques.
The reference values are:
- Absent : in an extemporaneous urine sample, ie taken at a single time of the day;
- 30-70 mg : in the urine of 24 hours.
The result can be expressed in milligrams of ketone bodies per deciliter of urine (mg / dl).
Note: the reference values may vary slightly depending on the laboratory that carries out the analysis and on the type of reference population (gender, age, etc.); the parameters reported in the report of the analysis center are therefore authentic.
High Ketones - Causes
The finding of ketone bodies in urine (ketonuria) is common in the following cases:
- Especially prolonged fasting (equal to or greater than 18 hours);
- During pregnancy;
- Isopropanol poisoning;
- People who follow ketogenic diets;
- burns;
- After surgery.
Other conditions that can increase the level of ketones in urine include:
- Alcohol abuse;
- Anorexia;
- Bulimia;
- Vomiting and diarrhea;
- Temperature;
- Hyperthyroidism;
- Severe malnutrition.
The accumulation of these substances in our body can have more or less serious consequences such as:
- General malaise;
- Numbness;
- Mental confusion;
- Intense thirst;
- Nausea and vomit;
- Abdominal pain
- Weight loss.
Chetonuria and Diabetes
The most characteristic condition accompanied by an increase in ketone bodies in urine is type I diabetes, where, due to high blood glucose levels, the intracellular availability of sugar is very low (due to the absence of insulin).
More rarely, ketone bodies are found in the urine of type II diabetics, for example in the phases of metabolic decompensation, acute infectious diseases (fever) or strong dietary restrictions undertaken in order to reduce blood sugar (for example the Atkins diet).
All diabetics should be tested for ketonuria during any type of intercurrent disease, when there is intense glycosuria and considerable hyperglycaemia (> 300 mg / dL), during pregnancy or in the presence of symptoms compatible with the diagnosis of ketoacidosis (nausea, vomiting, abdominal pain).
The determination of ketones in urine is widely used in the diagnosis of diabetes, in monitoring the insulin-dependent diabetic patient and especially in the evaluation of diabetic ketoacidosis (ketosis + hyperglycemia + blood acidosis: it represents an important medical emergency that can affect both the person with known diabetes that the diabetic of first diagnosis).
How to measure it
In the laboratory, the test can be performed on:
- A urine sample collected at a single time of day;
- A single sample of urine emitted during a whole day (24-hour urine; overall ketonuria), for example: from 8 am to 8 am on the following day;
- 3 urine samples (fractionated ketonuria), dividing the collection into 3 8-hour periods (example: morning 8-12, afternoon 12-20 and night 20-8).
In addition, self-assessment tests are available that measure ketonuria based on the color change of a test strip immersed in a urine sample at any time of day.
Preparation
Urine should be collected in a sterile disposable container. For some exams, it is necessary to collect all the urine emitted over a whole day (24 hours). In this case, large containers (2 to 3 liters) must be used.
How to perform the home exam
The search for ketones in urine can be performed at the hospital on a urinary sample, or at home, using strips to be immersed in the urine to measure the presence of ketones; in the latter case it is very important to respect the medical indications and those indicated on the packaging.
Based on the results (color taken from the strips), if you notice the presence of high concentrations of ketone bodies, it is good to proceed as advised by your doctor or alert him as soon as possible in case of doubt.
Interpretation of Results
Under normal conditions, ketone bodies cannot be found in urine, except in the smallest traces. Their concentration in the urine increases, instead, in the presence of an alteration of the metabolism.
In the case of excessive production, the ketone bodies flow into the bloodstream and from here, being harmful to the body, pass into the urine to be expelled, thanks to the purifying action of the kidney.
Ketonuria can occur in situations characterized by an increase in the degradation of fats for energy purposes, in relation to a reduced availability of glucose, which normally constitutes the main source of energy for the vital functions of the organism. This can occur in the event of prolonged fasting, unbalanced diets, chronic alcoholism, fever, pregnancy and diabetes.
Chetonuria and Diabetes
In diabetes, the finding of ketonuria reveals that the amount of insulin is insufficient to allow proper use of glucose by the body. This datum allows to adjust the therapy and prevent ketoacidosis, a serious complication due precisely to "poisoning" by ketone bodies.
In diabetic subjects, performing ketonuria self-assessment tests is recommended - with variable frequency, alongside that of glycaemia and glycosuria - in the case of:
- Insulin therapy;
- Flu or other febrile diseases;
- Pregnancy;
- Glycemic values not well controlled;
- Whenever the blood sugar level exceeds 240 mg / dl and symptoms compatible with ketoacidosis appear (such as nausea, vomiting and abdominal pain).
