Good use of biotests in emergency

1. Good use of biotests in emergency Dr. David Tran FVHospital 28 April 2010

2. Interest of a biotest • Can help the clinician to confirm or rule out a diagnosis (troponine, lipase, AgNS1, d.dimeres) • Can help the clinician to evaluate the general condition of a patient (uree, creatinine, proteine) • Can help the clinician to evaluate the seriousness of the illness (CRP, WBC, blood gaz)

3. Drawback of a biotset • Blood test > disturbance for the patient (child) • Increase the cost of cares. • Sometime difficult to perform (ECBU, blood gaz) • Increase the waiting time (2h for blood test) • Sometime difficult to interpret (d.dimeres, BNP)

4. The right questions before asking for a biotest • Is-it really useful? • Do I need this test in emergency? • Will the result modify the management of this patient? • Is it the right moment to ask for this test (troponine, NS1 Ag) • What is the probability to have an abnormal result?

5. Characteristic of a biotest • Sensitivity: Se = TP / TP + FN (Good Se = law false negative value) • Specificity: Sp = TN / FP + TN (Good Sp = law false positive value) • Positive Predictive Value: TP / TP + FP • Negative Predictive Value: TN / FN + TN

6. Biotest with good sensitivity (Negative predictive value > rule out test) • NFS or CRP (Appendicitis) • D. dimeres (Phlebitis) • BNP (cardiac failure) • Transaminases (hepatitis) • Urine test (renal colic, urine infection)

7. Biotest with good specificity(Positive predictive value > diagnosis tests) • Lipase (pancreatitis) • Troponine (myocardial infarction) • Hemocultures (septicemie) • LCR (meningitis) • Frottis sanguin (paludism)

8. Example of BNP and cardiac failureFigure 1: Characteristics of BNP testapplied to a hypothetical 1,000 people attending an emergency room with dyspnoea and suspected CHF • Few false negative value (good sensitivity) • A lot of false positive value (poor specificity) • Interest of BNP to rule out the diagnosis of CHF if the test is negative. • R Cardarelli, TG Lumicao. B-type natriuretic peptide: a review of its diagnostic, prognostic, and therapeutic monitoring value in heart failure for primary care physicians. Journal of the American Board of Family Practice 2003 16: 327-333. • JA de Lemos et al. B-type natriuretic peptide in cardiac disease. Lancet 2003 362: 316-322.

9. Limits of a biotest: exemple of NT-proBNP • Non cardiac sources of variation of NT-proBNP (age , female, renal function, obesity ) • Other cardiac conditions increase the values of NT-proBNP (atrial fibrillation, aortic stenosis) • Problem of gray zone (indecision zone)

10. 0 100% 50% 90% 5% Autre diagnostic Intervention Indécision Autres tests Seuil d’abstention Seuil d’intervention Influence of a biotest on the decision = post-test probability • Usual biotests influence diagnosis or treatment in only less than15% Sandler G. Do emergency tests help in the management of acute medical admissions ? Br Med J (Clin Res Ed) 1984 Oct 13; 289(6450):973-7.

11. Example of d.dimeres for the diagnosis of deep vein thrombosis = importance of probability pre-test • Prevalence 10% (Wells score) > law probability • Prevalence 30% (Wells score) > intermediate probability • Prevalence 80% (Wells score) > high probablility Confirm DVT Need other test Rule out DVT Pre-test probability Post-test probability Likelihood ratio

12. Strategy for diagnosis of a dyspnea in A&E Patient coming with dyspnea • Temp., SpO2, Blood Pressure, Pulse • Physical examination • EKG • Chest Xray No evident diagnosis Evident diagnosis • CRP, NFS • Blood gaz • D dimeres • BNP +/- Troponin Specific treatment

13. Different steps of medical reasoning • Evaluation pre-test (clinic, prevalence, score etc) • Choose the right test (the one which will give us the answer to our question) • Evaluation post-test (confrontation between clinic and result of the test) • Decision (intervention or not, other test?)

14. Avoid useless biotest if no clinical orientation or if the diagnosis is evident • Ionogramme, coagulation are often useless in most of situations • Thyroide hormone dosage without typical signs of thyrotoxicosis or hypothyroide • Troponin is useless if no cardiologic orientation (chest pain and/or EKG anomalies) • D dimeres are useless in case of high clinical probability of pulmonary embolism or deep vein thrombosis (perform angio CT, or echo-doppler)

15. How to include a biotest in the medical reasoning ?

16. Case Report 1: female 58 years old, “vertigo sensation” for 3 days. Treatment for HTN with Amlor and Concor. Clinical exam finds TA 19/10, pulse 60/min., T37 • Clinical exam is normal (neuro, cardio, ORL). • EKG shows sinusal rhythm 60/min without abnormality • What kind of exam do you request?

17. Case report 2: A 3 years old boy consult for fever sine 4 days, with cough and runny nose • Alert, can eat & drink normally.T 36.8, RR 20/min, SaO2 96% • Auscultation normal, no rale, no murmur, abdomen supple, no organomegaly, supple neck, no vomiting, no diarrhea. • ENT: enlarge tonsils but no sign of infection (usual according the mother) • What test do you order: CBC, CRP, Ionogramme, Uree, Creat, ASAT, ALAT, Dengue NS1 or/and Dengue serology, Urine test?

18. Case report 3: A man 69 years old consult for inflammation at left leg appeared 1 day after a flight. Past history HTN, Hypercholesterolemia, Thyroide pb. • Pulse 85/min, TA 17/9, RR 18/min, SaO2 96% • Swollen left ankle with inflammation along the lower part of the left calf. No pain at the calf. Cardio-pulmonary exam is normal. • Doppler shows a superficial thrombosis of the internal saphene vein, no deep vein thrombosis. • What biotest(s) would you ask in the list below: Ionogramme, Glycemia, Uree-Creat, ASAT-ALAT-GGT, CRP, NFS, TP, TCA, D dimere, CPK, Groupe Rh x 2, Urine test, T4L-TSH?

19. Case report 4: a man 69 years old, treated with Digoxin and Furosemide for cardiac insufficiency, coming for “fatigue and dyspnea” since a few days • Clinical exam finds TA 11/7, pulse 40/min., mild crackles in the lungs and swollen legs. • EKG: What are you diagnosis hypothesis and what kind of exams are you going to ask?

20. Case report 5: A man 48 years old, coming for permanent chest pain for 2 hours. Risks factors smoke and overweight • Vital sign: TA 11/7, pulse 95/min, SaO2 95%, T37.8. • Clinical exam is normal (cardio/pulmonary) • What are your diagnosis hypothesis? • EKG: • What kind of exams are you going to ask to confirm you hypothesis?

21. Case report 6: a female 58 years old hospitalized 5 days ago for ankle fracture come to A&E for dyspnea and chest pain since the day before • Vital signs: pulse 95/min, TA 19/10, RR 20/min, SaO2 94%, T37.7 • Pain at left chest and shortness of breath, auscultation is normal • EKG: What kind of exam are you going to ask to confirm your diagnosis?

22. Interest of “bilan pre-op” for patient without severe history (ASA 1 or 2)* • CBC useful only if there is a risk of hemorrhage during surgery (hip fracture, colectomy, gastrectomy, etc) • TP, TCA, platelets are useful only if surgery at risk of hemorrhage • Ionogramme, Uree, Creat are useless if the is no clinical orientation and no medication. • Groupe ABO, Rh and RAI are not recommended if law risk of hemorrhage during surgery. * Examens pre-operatoires systematiques (ANAES 1998)