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Clinical Biochemistry: Understanding Tests and Results

Learn about clinical biochemistry tests, reference intervals, specimen collection, factors affecting ranges, and interpreting results. Explore case studies and understand the impact of abnormal biochemistry on diagnoses. Expert insights from Dr. Steve Smith.

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Clinical Biochemistry: Understanding Tests and Results

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  1. Clinical BiochemistryAn Introduction Dr Steve Smith Consultant Clinical Biochemist UHCW

  2. Clinical Biochemistry Meaurement of substances Measured In: Blood, Mainly serum but also cells Urine Cerebrospinal Fluid Faeces Kidney stones Saliva etc • Enzymes • Metabolites • Metal ions • Drugs and metabolites • Proteins • Hormones • Vitamins • Mutations in DNA & RNA • etc

  3. How do we do it? • 96% work is fully automated

  4. Reasons for requesting a Biochemistry test • Diagnosis (confirmation or rejection of clinical diagnosis) • Glucose, TSH • Monitoring (Progression or response to treatment) • TSH, HbA1C, Lithium, Tacrolimus, PSA • Prognosis (Information about the likely outcome) • Cholesterol, Lactate Dehydrogenase (teratoma) • Screening (detection of subclinical disease) • Phenylketonuria, FOBT, Cholesterol

  5. Specimen Collection • Obtaining the correct specimen is crucial • Blood Samples: • Venous or arterial • Specimen bottle • Transport • Time of day • Avoid damage to sample

  6. Questions which may be asked on receipt of Laboratory Results • ‘If the result is not what I expected can I explain the discrepancy?’ • ‘Does it differ significantly from previous results and will change my diagnosis or the way I treat the patient?’ • ‘Is it consistent with clinical findings?’ • ‘what do I do next?’

  7. How do we identify abnormal biochemistry? • 'The Normal Range’ • Defines the values of a biochemical test found in healthy subjects against which patient values can be compared. • Artificial concept - no clear boundaries exist. • Preferred term is 'Reference Interval'

  8. Defining the Reference Interval ‘Normal’ Subjects TestValue -2.5% +2.5%

  9. Some factors which affect reference ranges • Age • Gender • Diet • Pregnancy • Time of month • Time of day • Time of year • Weight • Stimulus • Method These need to be borne in mindwhen interpreting results

  10. Hormone changes during the menstrual cycle

  11. Some factors which affect reference ranges • Age • Gender • Diet • Pregnancy • Time of month • Time of day • Time of year • Weight • Stimulus • Method These need to be borne in mindwhen interpreting results

  12. Diurnal Rhythm of Cortisol

  13. Some factors which affect reference ranges • Age • Gender • Diet • Pregnancy • Time of month • Time of day • Time of year • Weight • Stimulus • Method These need to be borne in mindwhen interpreting results

  14. Monthly variation in 25-hydroxy Vitamin D levels in UK men and women

  15. Some factors which affect reference ranges • Age • Gender • Diet • Pregnancy • Time of month • Time of day • Time of year • Weight • Stimulus • Method These need to be borne in mindwhen interpreting results

  16. Alkaline Phosphatase Reference Intervals • 30 – 120 IU/L • 80 – 280 IU/L

  17. Ideal Diagnostic Test ‘Normal’ Diseased Frequency Concn. No false positives or negatives

  18. Comparisons with Disease Groups ‘Normal’ Diseased TestValue +2.5% FalseNegatives FalsePositives

  19. Comparisons with Disease Groups ‘Normal’ Diseased TestValue FalseNegatives FalsePositives

  20. Different Ranges • Reference Interval (Range) • Urea • Therapeutic Range • Phenytoin • Clinical Cut Off • Cholesterol, B-Type natriuretic peptide

  21. Comparisons with Disease Groups ‘Normal’ Diseased TestValue +2.5% FalseNegatives FalsePositives

  22. Is the change significant?

  23. Is the change significant? • A GP measured the serum creatinine of a 41-year-old man newly diagnosed as having diabetes and hypertension. The result was 105 mol/L. Six months later, both conditions were well controlled and the test repeated.

  24. Is the change significant? • Investigation • Serum creatinine = 118 mol/L (105 mol/L previous) • Patient was alarmed at the increase and the GP uncertain whether the change was significant.

  25. Is the change significant? • Analytical Variation • Biological Variation • Extrinsic • Time, posture, stress. • Intrinsic

  26. Is the change significant?

  27. A 4 year old boy was seen in the paediatric out-patients’ department because of hepatomegaly, metabolic acidosis, and growth retardation. Some of his abnormal blood test results are: • Glucose 2.0 mmol/L (3.0 – 5.6 ) • Uric Acid 610 μmol/L (200 – 430 ) • Lactic Acid 3.7 mmol/L (0.5 – 1.5 ) • Cholesterol 5.4 mmol/L (<5.0 ) • Triglycerides 6.7 mmol/L (0.5 – 1.5)

  28. Finding a low glucose is common in paediatrics and it triggers a whole raft of tests. • Hypoglycaemia is a feature of many inborn errors of metabolism

  29. Von Gierke’s Disease • This case Glucose-6 phosphatase deficiency • Hepatomegaly due to excess glycogen stores • Raised urate due to raised lactate • Abnormal lipids due to lack of glucose • Lactate raised because G6P taken down a pathway to lactate not glucose.

  30. Demonstrates the knock on effects from what a first might appear common; low glucose.

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