Nutritional Biochemistry Lecture Notes PDF

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27th November 2020

Sophie Green

Nutritional Biochemistry Where does nutritional biochemistry fit?

A= Anthropometry, for example weight, height and other measures B = Biochemistry (considered here) C = Clinical Data (nature of condition, treatment and associated information) D = Dietary information (diet history, nutritional problem and associated information) E = Energy requirements and Environmental (including psychosocial, socioeconomic, functional capacity, geography etc.)

Background to nutritional biochemistry:      

Infection injury Fluid balance Electrolyte problems Presence of disease Progress of disease or treatment Organ dysfunction

(do not consider biochemistry in isolation)  

Over 70% of patients require some form of biochemical test Results often fall within a “normal range” which allows specific conditions to be ruled out

Clinical sample: material collected from a patient and investigated (e.g. blood, urine, faecal, tissue and other body fluids) Analyte substance tested in sample (e.g. potassium, glucose, albumin)   

Blood collected in plain tube and allowed to clot, after centrifugation a serum specimen is obtained Blood collected in a tube with an anticoagulant (such as heparin), after centrifugation plasma is obtained Point of care testing of whole blood is available e.g. glucose levels on wards or in clinics

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green  

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Potassium and calcium are not compatible with life Blood was initially collected into a tube containing (potassium) fluoride and oxalate used for routine glucose measurement Sample then transferred to plain tube for analysis in the lab

Many factors can influence a result from a biochemical test:

Important terms: Precision: reproducible and reliable (reliability) – gives same result over repeated trials Accuracy: exact and specific (specificity) – it measures what is supposed to measure Biochemical tests need to specific and sensitive: Specificity: incidence of negative results in people who do not have a disease Sensitivity: incidence of positive results in patients who have the condition

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green Fluid and Electrolytes:

Osmolality is a measure of how much one substance has dissolved in another substance. The greater the concentration of the substance dissolved, the higher the osmolality.

Figure 1 - Major Ions

Body and blood water:   

Water intake and dietary intake Water losses (urine, insensible losses) Increased plasma osmolality detected by osmoreceptors in the hypothalamus:  Stimulation of thirst  Antidiuretic hormone (ADH) / Arginine Vasopressin (AVP)  Vasopressin leads to water retention, reduced urinary output  Leads to corrected osmolality

Sodium Balance:      

3,700 mmoles in average adult, 75% in ECF and 25% in bones & tissue Sodium intake variable: 100-200 mmol/day Sodium losses variable: Most excretion is via kidneys (close intake in health). Also lost in sweat (approx.. 5 mmol/day) and faeces (approx.. 4 mmol/day) Aldosterone decreases urinary sodium excretion by increasing sodium reabsorption In disease gastrointestinal tract is often a major cause of losses e.g. diarrhoea

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green Sodium:    

Reference range: 135-145 mmol/L Hyponatraemia – below the reference range Hypernatraemia – above the reference ranges Hyponatraemia = commonest electrolyte disorder

Hyponatremia

Case Study – Mr Buckingham: A 48 year old male presents with a 2 day history of severe diarrhoea and some vomiting. He has been struggling to eat but has managed to drink water His blood pressure is 100/55 mmHG and pulse 105/minute His biochemistry results are: Sodium 131 mmol/L, Potassium 3.0 mmol/L, Urea 15.7 mmol/L and Creatinine 150 µmol/L Diagnosis: Hypernatremia Due to either  Water loss (e.g. increased GI loss, burns, insufficient intake, diabetes insipidus, osmotic diuresis in diabetes mellitus)  Sodium gain (less common e.g. sodium administration, Conn’s syndrome, Cushings syndrome)

HUG 2319 Nutrition and Metabolism for health and disease

Sophie Green

27th November 2020

Potassium:     

Reference range: 3.5-5 mmol/L Hypokalaemia – levels below the reference range Hyperkalaemia – levels above the reference range Potassium measurements in clinical chemistry are one of the most sensitive to artefact error, usually errors in collection, handling and / or storage of samples E.g. haemolysis of samples

Hypokalaemia

Case study – Mrs McVie: Mrs McVie is 77 years old and is taking medication for heart failure and associated symptoms. Mrs McVie’s GP checked her U&Es after at her follow up appointment Her biochemistry results are: Sodium 143 mmol/L, Potassium 2.4 mmol/L, Urea 8.7 mmol/L and Creatinine 141 µmol/L Diagnosis: Hyperkalaemia

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green Hyperkalaemia Causes:

Bicarbonate    

Reference range: 24-29 mmol/L Critical values 40 mmol/L Used along with blood gas and pH measurements to determine acid-base balance E.g. metabolic acidosis, metabolic alkalosis

Urea and Creatinine:   

Plasma urea is produced by deamination of amino acids Elimination in urine = major route for nitrogen excretion Reference range for Urea: 3.3-6.7 mmol/L

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Plasma creatinine concentration = insensitive measure of glomerular function Normal plasma creatinine not necessarily = normal renal function Plasma creatinine relates to muscle bulk; can be influenced by a protein rich meal and exercise Reference range: Male adult = 59-104 μmol/L Female adult: 45-84 μmol/L

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HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green Causes of abnormal urea and creatinine

Liver function tests (LFTs):  

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Misnomer as not really tests of ‘liver function’ Can help0 to determine prognosis and monitor response to treatment Typical measurement of liver function tests will include:  Aspartate aminotransferase (AST)  Alanine aminotransferase (ALT)  Bilirubin  Alkaline Phosphate (ALP)  Gamma-glutamyl transferase (GGT)

Plasma proteins are also important:   

Albumin is synthesised in the liver and its concentration in the plasma is in part a reflection of the functional capacity of the organ Albumin decreases in chronic liver disease, but can be normal in acute hepatitis due to its long half-life Can also look at Prothrombin Time (PT); examines the clotting activity and reflects the synthesis of clotting factors by the liver

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green Liver function test changes: Mild to moderate elevations:   

Fatty liver (diabetes, obesity, alcohol abuse) Chronic Hepatitis B and C Medications:  Pain relief – asprin, ibuprofen  Anti-seizure – phenytoin  Cholesterol lowering – atovastaton, simvastatin  Antibiotics – fluconazole, tetracyclines

Albumin and acute phase proteins Physiological changes after trauma, burns, infection, inflammation and other conditions. Mediated by cytokines (e.g. interleukin 1 and 6), tumour necrosis factor and raised concentrations of cortisol and glucagon.

Albumin and CRP: Albumin alone is a POOR MARKER OF MALNUTRITION CRP reference range < 10 mg/L, and levels change rapidly CRP IS USED TO ASSESS INFLAMMATORY RESPONSE

Haematology      

Infection and inflammation, e.g. White blood cell count (WBC), Erythrocyte Sedimentation Rate (ESR) and Neutrophils Reference range: WBC 4.0-11.0 x 109 / L Haemoglobin (Hb) levels influenced by iron deficiency anaemia, surgery / trauma, blood products / infusions Reference range Hb: Males – 130-180 g/L Females – 115-165 g/L

HUG 2319 Nutrition and Metabolism for health and disease

27th November 2020

Sophie Green

Case study – Mr Mayall: Mr Mayall was admitted 3 days ago for emergency knee surgery. He has started eating today and has been receiving IV fluids since his operation. He is apyrexic. His biochemistry results are: Sodium 140 mmol/L, Potassium 4.2 mmol/L, Urea 4.5 mmol/L, Creatinine 90 µmol/L, Albumin 33 g/L, CRP 49 mg/L, WBC 9.0 x 109/L, Hb 10 g/L

Glucose Reference range:   

Fasting blood glucose: 3.5 to 5.0 mmol/L Random blood glucose: 3.5 to 8.0 mmol/L 2 hours post prandial glucose

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Normoglycaemia – normal blood or plasma glucose Hypoglycaemia – reduced blood or plasma glucose Hyperglycaemia – raised blood or plasma glucose

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HUG 2319 Nutrition and Metabolism for health and disease

Sophie Green

27th November 2020

Interpretation of results:  

Blood glucose < 2.2 mmol/L Severe hypoglycaemia, associated with brain damage Blood glucose > 25 mmol/L Severe hyperglycaemia, may result in immediate life threatening complications of diabetes mellitus, e.g. diabetic ketoacidosis or hyperosmolar (non-ketotic) coma

Vitamin D  

Synthesised from cholesterol in the skin, and activated in liver and kidney Active form of vitamin is I, 25 (OH) 2 D3 or Calcitrol

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Vitamin D is important for bone health Recent recommendations from SACN suggest an RNI of 10μg/d for UK popukation

HUG 2319 Nutrition and Metabolism for health and disease...