Case studies

CASE STUDY 1:
A 20 year old male, a known insulin-dependent diabetic, was brought to hospital in a coma. Analysis of a blood sample gave the following results:
Analyte
Patient
Reference(*)
glucose
41mM
3.0 - 5.5mM
acetoacetate
2.6mM
<0.20mM
-hydroxybutyrate
12.0mM
<0.25mM
HCO3-
7mM
23-33mM
urea
10.1mM
3.0 - 8.0mM
* The reference values refer to the concentrations in a “normal” patient.
Why is [glucose] high?
The patient described in this case study is a known case of Insulin-dependant diabetes mellitus (Type 1 Diabetes Mellitus). Type 1 DM is a metabolic disorder resulting from the autoimmune destruction of the pancreatic beta cells located in the Islets of Langerhans which results in a progressive disability to secrete insulin (Votey & Peters, 2007). Type 1 DM can present at any age the most common presentation being in childhood, as in this case, but one-fourth of cases are diagnosed in adults. (Levitsky & Misra, 2008).
The destruction of pancreatic islet cells in patients with Type 1 DM leads to an absolute or relative deficiency of insulin, which is a key enzyme involved in the metabolism of glucose, resulting in hyperglycemia and abnormal carbohydrate, fat and protein metabolism. The patient in this case is currently suffering from Diabetic Ketoacidosis (DKA). In this condition, the hyperglycemia is multifactorial, resulting not only from the underutilization of glucose, occurring due to insulin deficiency, but also from overproduction (Charfen & Fernandez-Frackelton, 2005, pp. 610-611). DKA is a state where insulin deficiency is compounded by an increase in the counter-regulatory stress hormones such as glucagon and cortisol. These hormones result in the overproduction of glucose via the processes of glycogenolysis (conversion of glycogen into glucose) and gluconeogenesis (de novo production of glucose in the liver) (Charfen & Fernandez-Frackelton, 2005, p. 611; Wallace & Matthews, 1997, p. 773). Thus, it is the combination of glucose underutilization and overproduction that leads to hyperglycemia in diabetic patients presenting with DKA.
What are acetoacetate and β-hydroxybutyrate, and how are they produced in the body?
Acetoacetate, β-hydroxybutyrate and Acetone are products of fatty acid metabolism which are termed as ‘Ketone Bodies’ or simply ketones (Wallace & Matthews, 1997, p. 773). These substances are weak organic acids and when they accumulate in the human body, they can lead to metabolic acidosis (Charfen & Fernandez-Frackelton, 2005, p. 611). In DKA, the insulin deficiency and increased levels of stress hormones result in an increase in the process of lipolysis, i.e. the production of acetyl CoA from fatty acids (Wallace & Matthews, 1997, p. 773). In addition to increased lipolysis, there is inhibition of lipogenesis which prevents the acetyl CoA from being utilized via the TCA cycle. Instead, acetyl CoA is oxidised into acetoacetate and β-hydroxybutyrate via the HMG-CoA pathway which occurs exclusively in the hepatic mitochondria, resulting in ketonemia (i.e. the presence of ketones in the blood) (Charfen & Fernandez-Frackelton, 2005, pp. 611-612; Newsholme, Leech, & Board, 2010, pp. 138-139).
Explain the concent...