Using the laboratory and interpreting results

1. Using the laboratory and interpreting results Ruth Lapworth Consultant Clinical Scientist CPD Talk November 2010

2. Sample transported to laboratory Sample taken Sample received, labelled and entered into Laboratory Information System (LIS) Clinician generates request LIS Pre analytical Sorting and distribution Labelling Decapping Centrifugation Clinician review and action Data Manager Analytical Clinical Chemistry Immunoassay Haematology Esoteric Analyses Sample Storage Report generated Result authorisation and interpretation

3. Good and bad reasons for requesting a laboratory test Examples from recent request forms Patient Clinical Details Test(s) Female – 40 years none PSA Male – 60 years gets it every yr glucose, PSA Female – 69 years hay fever BNP Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

4. Good reasons for requesting a laboratory test • To establish a diagnosis • To exclude a diagnosis • To monitor treatment • To detect disease recurrence • Therapeutic drug monitoring • Adherence to guidelines Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

5. Bad reasons for requesting a laboratory test • Substitute for thought • Delaying tactic • Test available • Consultant may want it • Prop to morale • Medico-legal safeguard • Patient demand Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

6. Types of Result • Diagnostic opinion • Positive/negative • Numerical • reference range • therapeutic range • target value • odds ratio • cumulative Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

7. Numerical results – reference range Female 69 years - admitted A&E Sodium * 115 mmol/L (135 – 145) Potassium * 3.4 mmol/L (3.5 – 5.1) Creatinine 66 umol/L (44 – 80) GFR (estimated) 79 units=* Total Protein 66 g/L (64 – 83) Albumin 40 g/L (35 – 50) Globulin 26 g/L (20 – 35) Total Bilirubin 17 umol/L (0 – 17) Alkaline Phosphatase 67 U/L (42 – 128) ALT 16 U/L (0 – 50) Calcium * 2.0 mmol/L (2.1 – 2.6) Albumin-corrected calcium * 2.0 mmol/L (2.1 – 2.6) CRP <1 mg/L (0 – 10) Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

8. Numerical results – target value Troponin I – 0.04 ug/L The decision threshold for significant cardiac ischaemia is )= 0.05 ug/L. Raised concentrations may also be seen in non-ischaemic cardiac dysfunction (e.g. pulmonary embolism, cardiac failure, myocarditis, renal failure). Troponin I must not be interpreted in isolation – see EKHUFT guidelines via Trust Net Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

9. Synacthen Test Cortisol – 30 min post dose inadequate < 450 nmol/L equivocal 450-479 nmol/L adequate > 480 nmol/L Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

10. Terminology of reference values (1) Reference individuals constitute a Reference population from which is selected a Reference sample group on which are determined Reference values Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

11. Terminology of reference values (2) on which is observed a Reference distribution on which is calculated Reference limits that define a Reference interval (range) No 2.5% 97.5% concn Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

12. Reference Ranges • Usually chosen to include 95% of healthy individuals • 5% of results therefore fall outside reference range • Ordering several tests increases the chance of a healthy person having at least one abnormal result Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

13. Reference Ranges (cont) Number of tests Probability of at least ordered one abnormal result 1 5% 2 10% 5 23% 10 40% 15 54% 20 64% Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

14. Factors that can affect laboratory results • Analytical errors • Pre-analytical influences • Inherent biological variation Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

15. Serum Creatinine 100 mol/L Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

16. eGFR • Estimate of glomerular filtration rate • Derived from a formula that includes serum/plasma creatinine measurement 4-variable modification of diet in renal disease (MDRD) equation • Serum creatinine • Age • Sex • Ethnic origin (multiply by 1.212 for african-caribbean people) • Reported in ml/min/1.73m2 Ruth Lapworth CPD Talk Consultant Clinical Scientist November 2010

17. Is this result significantly different from the last one? Date HbA1C (%) Aug 07 7.3 Feb 08 6.9 Sept 08 6.8 Feb 09 7.0 Aug 09 53 Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

18. Male 90 YearsCVA and aspiration pneumonia Na 88 mmol/L K 11.9 mmol/L Cr 81 μmol/L T.Prot 32 g/L Alb 13 g/L T.Bili 8 μmol/L ALKP 62 U/L ALT 18 U/L ▲ drip – arm sample Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

19. Male 54 YearsRenal failure, on dialysis Na 183 mmol/L Potassium 5.5 mmol/L Chloride 94 mmol/L Creatinine 421μmol/L eGFR 10 units ▲ Citralock contamination Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

20. Female 67 YearsRoutine check (GP) Na 136 mmol/L K 3.8 mmol/L Cr 83 μmol/L T.Prot 71 g/L Alb 42 g/L T.Bili 11 μmol/L ALKP 77 U/L ALT 188 U/L CK 14019 U/L ▲ on statin Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

21. Female 74 Years?Addisonian crisis Synacthen test Time Cortisol (nmol/L) 0’ >2000 30’ >2000 ▲ on hydrocortisone! Ruth Lapworth CPD Talk Consultant Clinical Biochemist November 2010

22. Using the laboratory and interpreting results Ruth Lapworth Consultant Clinical Scientist CPD Talk November 2010