The Purple Book

Other Chemistry

• redistribution - associated with major surgery fluid shifts, insulin/glucagon/adrenaline use, respiratory alkalosis
  • beware esp in Rx of hyperglycaemia, DKA (osmotic losses + redistribution with insulin)
• decreased absorption - malnutrition, alcohol Xs, anorexia
• increased renal loss - associated with diuretics
• renal replacement therapies - loss in effluent with large fluid shifts
• Clinical - muscle weakness, CNS changes, poor WCC function reducing resistance to infection, arrhythmias
• Treatment - depends on level:
  • <0.64mmol/l & asymptomatic - preferably enteral replacement (Phosphate Sandoz tablets contain 500mg elemental phosphorous - 4-6 tablets daily for adults, 2-3 for kids)
  • <0.32mmol/l or symptomatic - parenteral replacement

• Iron level - measure of circulating iron
• Transferrin - main transport protein. Synthesis inversely proportional to body stores of iron.
• Ferritin - main storage protein.
• TIBC (total iron binding capacity) - sum of serum Iron and unbound capacity of Transferrin.

Iron deficiency without anaemia is associated with:

• weakness, fatigue, reduced exercise performance, difficulty in concentrating, and poor work productivity
• neurocognitive dysfunction including irritability
• fibromyalgia syndrome
• restless legs syndrome
• symptom persistence in patients treated for hypothyroidism

Child Pugh score

• Hyperlactaemia results from either excessive production or reduced clearance
• Commonly classified as Type A: due to tissue hypoxia, and Type B: no evidence of tissue hypoxia
• Hyperlactaemia acronym - LACTATES
  • Liver and lung: impaired hepatic metabolism: increased production in acute respiratory disease
  • Accelerated aerobic glycolysis: sympathomimetics exceeds capacity of pyruvate dehydrogenase to convert pyruvate to lactate, severe exercise
  • Congenital mitochondrial disease: inborn errors of metabolism particularly in infants and children. (pyruvate dehydrogenase deficiency)
  • Toxic and drug effects - eg mitochondrial dysfunction from cyanide, nucleoside reverse transcriptase inhibitors (anti-virals) and toxic alcohols, as well as the effects of metformin (some debate).
  • Anaerobic metabolism: severe exercise
  • Thiamine deficiency: inhibits pyruvate dehydrogenase
  • Extracellular efflux of lactate from the intracellular to the extracellular compartment, which can occur in alkalosis. This is known as “lactic alkalosis” and is thought to be a consequence of the effect of alkalosis on an H+-linked cell membrane carrier mechanism
  • Sepsis: multifactorial, including cytokine-mediated enhancement of glycolysis and inhibited pyruvate dehydrogenase activity

• important marker in diagnosis of Heart Failure and can be normal in stable, treated, chronic HF
• NICE guidance for result in symptomatic patients:
  • >2000ng/L - assess by HF specialist within 2/52
  • 400-2000 - assess within 6/52
  • <400 - unlikely but does not exclude HF - see pitfalls
• pitfalls
  • higher levels - renal dysfunction, age, female sex, AF, inflammation, hyperthyroidism, use of sacubitril/valsartan
  • lower levels - obesity, immediately after acute coronary syndrome onset, and pericardial effusion
• range varies with age:

solid line = 50th centile dotted line = 97.5th centile

Urea-Creatinine Ratio

• whilst urea and creatinine are freely filtered by the kidneys, there is tubular reabsorption of urea but NOT of creatinine. The ratio can therefore be used as an indicator of a likely cause of renal failure

paradoxically accompanied by signs of deficiency, - a functional deficiency linked to qualitative abnormalities,eg. defects in tissue uptake and action of vitamin B12 high levels not infrequently associated with solid tumours:

• myeloproliferative blood disorders
• hepatocellular carcinoma (HCC) and secondary liver tumours
• breast cancer, colon cancer, cancer of the stomach and pancreatic tumours.

QJM Review of raised vitB12 in clinical practice