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Biochemical tests in clinical medicine lect1
- 1. Biochemical tests in clinical medicine Dr. Hala Kamel MBChB, MSc, MD Assist. prof. Biochemistry Dep., Faculty of Medicine ASU & UQ
- 2. Clinical Biochemistry History Clinical Examination Diagnostic services Laboratory services Clinical Biochemistry
- 3. Clinical Biochemistry Laboratory Clinical biochemistry Laboratory play an important, often unrecognised role, in disease diagnosis and the monitoring of treatment. •They are responsible for most laboratory testing performed on samples sent to the diagnostic laboratory by medical practitioners. •Laboratory results produced by MLS‟s are used by medical staff in the diagnosis of disorders in approx. 70% of all patient cases.
- 4. Clinical Biochemistry • Analysis of the chemical constituents of the blood, urine, faeces and tissues. • Most of the laboratory testing uses sophisticated instrumentation interfaced to a laboratory information system. • Diseases such as diabetes, renal failure, heart attack, drug analysis and hepatitis are some of the conditions investigated by clinical biochemists.
- 5. Introduction • Clinical Biochemistry • Dissolved elements in body fluids • Concentration and type e.g. glucose, electrolytes, hormones and significance of levels and interpretation. • Accurate and precise laboratory measurements can aid in diagnosis and management of disease
- 7. Uses of Biochemical tests • 1- Diagnosis • 2- Screening • 3-Prognosis • 4- Treatment
- 8. Use of Biochemical Tests • 1-Diagnosis • History and Physical Examination of patient --form Differential Diagnosis i.e. Hypothesis • Lab tests and Radiology to support or reject hypothesis. Limitations of tests must be appreciated • Interpretation must be carefully done in context of clinical details
- 9. 2-Screening • Detection of sub-clinical • Neonatal screening PKU, CHT • Criteria for same. • Natural history known • Acceptable tests no false negatives, few false positives • Ease of treatment • Positive outcome
- 10. Screening • Natural history of disease • Acceptable and reliable screening Tests, FP issues • Therapy available • Prevalence • Entire population • or “at risk groups”
- 11. 3-Prognosis • Serial tests to identify progressive disease creatinine in renal failure • Tests to identify risks of disease in future in certain groups cholesterol in “at risk families” • Calculation of risk depends on epidemiological data • Likely outcome of disease
- 12. Sampling • Test Request • Clinician requests that analysis be conducted. • Requirements • Name, DOB, Gender, Hos. No. MRN • Ward, Address • Requesting Clinician • Hypothesis / Problem • Tests sought,time of sampling,date • Clinical details, Drugs or Therapy.
- 13. Sampling Issues. • Patient Centred Factors • Age • Gender • Posture • Physiological State • Pregnancy • Exercise • Fasting / Fed • Time
- 14. Sampling contd. • Plasma,serum • Bottle and preservative, anti coagulant used • Age of sample • Time of sampling • Guidance from lab on sample requirements • Correct label • Transport • High risk specimen.
- 15. Variation Patient Variables : • Age, gender, fasting, time of day, exercise, posture, need to document these. • Biological Variation • Pre-Analytical Variation • Sample site, type of bottle • Transportation to lab. • Stability of analyte age • Analytical Variation • Post Analytical Interpretation
- 16. Analysis • Accuracy & Precision • Detection limits • Specificity& sensitivity • quality assurance • reference ranges
- 17. Precision and accuracy • Precision is the reproducibility of an analytical method. • If there is 2 methods performed for the same analyte repeated measurement of the same analyte will show more closed results to each others ( less scattering ) • Repeated measurement of an analyte will be close to each other if precise
- 18. Precision and accuracy • Accuracy defines how close the measured value is to the actual value. • Accuracy is therefore poor, as if the „sights‟ are off. so repeated measurement of an analyte is accurate if it is very close to actual value known before • It is the objective in every biochemical method to provide good precision and accuracy. • Automation of analyses has improved precision in most cases.
- 20. Diagnostic Sensitivity Positive test result in presence of disease. Diagnostic Specificity Negative test result with no disease. Diagnostic Sensitivity = TP TP + FN Diagnostic Specificity = TN FP+ TN
- 21. Analytical sensitivity and specificity • The analytical sensitivity of an assay is a measure of how little of the analyte the method can detect to improve the detection limit to help in discrimination normal results and those with suspected disease( Positivity in disease) • Analytical specificity of an assay relates to how good the assay is at discriminating between the requested analyte and potentially interfering substances. So it measures the negativity in normal results
- 22. ROC CURVES A,B,C
- 23. Test Efficiency and Predictive Values TE = TP +TN X 100 Total No. of Tests PV Pos = TP X 100 TP + FP PV Neg = TN X 100 TN + FN
- 24. Features of PD pos. and PD neg. • Prevalence of disease in population. • Low prevalence with less than 100% specificity high FP will result in low PV • Screening with follow up testing should have a high PV neg.
- 25. Likelihood Ratios • LR pos = Sens. /1 – Spec. • LR neg = Spec. / 1- Sens.
- 27. Reference Ranges • Mean ± 2SD Mean -1SD +1SD -2SD +2SD
- 28. Healthy and Diseased Reference range healthy diseased
- 32. Biological Factors affecting interpretation • Sex • Age • Diet • Time of sampling • Stress and anxiety • Posture • Exercise • Medical History • Pregnancy • Menstrual cycle • Drug History
- 33. Is It Different? SD2 = SD2 anal + SD2biol.
- 34. Receiving the report • Does the results fit in with the excepted? • If not, how to explain the discrepancy? • How can the results change the diagnosis? • How to manage that patient? • What should be done?
- 35. Interpretation • Is Result Normal? • Has it changed? • Does it support the clinical hypothesis?
- 36. Does it Support the Hypothesis? • Consistent support diagnosis • Inconsistent needs explanation • Error in sampling, patient labelling analysis,or reporting. • Repeat test • ? Diagnosis • Statistical random event abnormal test no disease. • Diagnostic Utility : Sensitivity, Specificity
- 37. Errors • Pre-analytical • Analytical • Post-analytical, • Interpretation, • Delays • Wrong records
- 38. Biochemical tests performed outside laboratory (Blood) Point of care testing Analyte Test when investing Operator Blood Gasses Glucose Urea/Creatinine Bilirubin Salicylates /Paracetamol Therapeutic drugs Acid – Base status DM Renal disease Neonatal Jaundice Detection of poisoning Compliance or toxicity Medical or Nursing setting Glucose cholesterol Diabetic monitoring Coronary heart disease risk Home or clinical setting Alcohol Fitness to drive/ confusion ,coma Alcohol test
- 39. Biochemical tests performed outside laboratory (Urine) Analyte Test when investing Operator Ketones Protein Red cells/Hemoglobin Bilirubin Urobilinogen PH Diabetic ketoacidosis Renal disease Renal disease Liver disease/ Jaundice Jaundice/ Haemolysis Renal tubular acidosis Medical or Nursing setting Glucose hCG D.M. Pregnancy test Home or clinical setting
- 40. POCT: Advantages • Faster stabilization of life-threatening crises (eg drug overdose, electrolyte disturbance) • Immediate risk stratification (eg chest pain) • Closer therapeutic management (eg diabetes) • Better patient compliance with therapy (diabetes, anticoagulation, hyperlipidaemia) • Reduce: – repeat clinic/practice visits – length of stay in hospital – complications (intra- & postoperative) – use of blood products (surgery)