Presentation on theme: "INTERPRETING LABORATORY RESULTS. With continuous medical education & research we have identified newer risk factors, etiologies & management strategies."— Presentation transcript:
With continuous medical education & research we have identified newer risk factors, etiologies & management strategies which has led to the current concept of “Evidence Based Medicine” & “Laboratory Medicine. Simultaneously, there are newer techniques & methods which are made available for investigating these new factors, there by aiding the clinician for disease diagnosis as well as its management. Hence, “Disease Diagnosis” today is “Investigation Based”. What do Unexpected Results Mean ? Thus, when confronted with an unexpected or abnormal test result one should take into consideration the various test variables which can contribute & there by explain the result variation apart from laboratory error & change in patient’s clinical status.
Interpreting laboratory tests – For evaluating these test results, one has to develop a systematic approach for their correct interpretation & this would include - A good clinico-pathological correlation - Recognizing & understanding the conditions required for testing a particular biologic parameter.
PRE-ANALYTICAL VARIATIONS These can be broadly divided into three categories 1.Physiological factors 2.Specimen collection & handling 3.Endogenous variables –like drug interferences, circulating antibodies
PRE-ANALYTICAL VARIATIONS 1. PHYSIOLOGIC / BIOLOGIC VARIATIONS These can be subdivided into - Diurnal Intraindividual physiological variations (Serial tests) - Age related variable reference ranges (Neonate\Child\Adult\Geriatric)
ANALYTES THAT DISPLAY CONSIDERABLE BIOLOGIC VARIATION - TESTAGE RELATED BIOLOGIC VARIATIONDIURNAL PHYSIOLOGIC VARIATION Potassium-1.0 – 1.2 Creatinine-0.04 – 0.20 GlucoseIncreases by 20-30% in > 45 yrs5.8 – 26.0 Magnessium-0.04 – 0.2 AlbuminDecreases upto 2 %> 45 yrs0.1 – 0.4 ASTIncreases upto 20% for men & upto 30% for women > 45 yr 5 -20 ALT5 - 28 Calcium-0.2 – 0.7 CholesterolIncreases upto 30-40mg%> 45 yr20 - 36 TriglycerideIncreases by 30% > 45 yrs30 - 100 CK-40 - 60 LDH-50 - 90 Amylase-20 - 45 HemoglobinDecreases by 1-2% > 45 yrs0.4 – 0.9 HctDecreases by 1-2 % > 45 yrs2 - 3 % WBCDecreases by 5 % > 45 yrs500 - 1900 Platelets-9,000 – 12,000 PT-INR-0.19 – 0.84
PRE-ANALYTICAL VARIATIONS 2. Specimen collection & handling – - Test pre-requisites - Phlebotomy & blood collection - Type of sample - Blood anticoagulation - Quality of sample - Transport of sample
Test pre-requisites 24 hr Urine collection in prelabelled container with necessary preservatives. Urinary 17-keto steroid, 17-OH corticosteroid, 5-HIAA, VMA, porphobilinogen require HCl 10-15 ml Urinary Proteins, uric acid, creatinine require boric acid 15 gms
1. Sample collection site - preferably other than the IV infusion site & in appropriate pre-labeled anticoagulant vial\tube. Use of serum separator tubes help in easy, fast separation of serum & reduce the serum-clot contact time 2. Order of draw affects the quality of the sample and can lead to erroneous test results due to contamination with the additive from the previous collection tube (CLSI H3-A5 standard) Phlebotomy & blood collection
TEST% INCREASE Total protein4.9 Cholesterol6.7 Creatine Kinase5.8 AST9.3 CHANGES IN TEST RESULT WHEN PHLEBOTOMY TOURNIQUET IS PROLONGED FROM 1 MIN TO 3 MINS Phlebotomy & blood collection CHANGES IN TEST RESULT WHEN PHLEBOTOMY PERFORMED USING TOURNIQUET- FOR TEST PARAMETERS CALCIUM & CPK
TESTARTERIALCENTRAL VENOUS PERIPHERAL VENOUS ALT626181 AST20 32 Albumin22.214.171.124 Creatinine126.96.36.199 Potassium43.93.6 Creatine Kinase807894 Platelet count1.00.901.24 Capillary value > venousCapillary value < venous Glucose 1.4%Bilirubin 5.0 % Potassium 0.9%Calcium 4.6 % Total protein 3.3 % Type of sample
Sample Quality – Falsely highFalsely low HemolysisLDH, AST, ALT, CK,Potassium Bilirubin,Albumin, Alk PO 4,γ- GT LipaemicHemoglobin, total proteinsCreatinine, Urea, AST, ALT, CK IctericHemoglobin, total proteinsCreatinine, Albumin, Amylase
Transport of sample Factors to be considered during sample transport are 1. Transit time - Eg. Serum PTH, Plasma lactate, plasma ammonia 2. Temperature- Eg. CD4 count, Coagulation & Hormonal assays 3. Packaging – to avoid any leakage & maintain Cold chain
PRE-ANALYTICAL VARIATIONS 3. Endogenous variables Drugs can cause analytical interferences – for common analytes like Hb, glucose, total proteins, s. creatinine & serum electrolytes. They cause interferences by - changing the serum or plasma matrix (i.e. reduction in proteins, increase in co volume of solutes(osmolality), redistribution of electrolytes(pH)) (eg.IV fluids) - sometimes in vitro hemolysis (eg. Salicylates) - enzyme inhibition(eg.cephalosporins, aminoglycosides & creatinine, vitamin C & G6PD). Circulating antibodies – Especially autoantibodies(eg. SLE,RA), paraproteins(eg. CLL/SLL, Myeloma) can cause spurious results for uric acid, creatinine, WBC & Platelet counts
ANALYTICAL VARIATIONS These contribute minimally in the test variation because –Manual methods are replaced by Automation –Strict Quality Control (Internal & External) Factors contributing in this variation are -Quality of water used for reconstitution of reagents/calibrators/controls or probe rinsing -Stability of reagents/calibrators/controls & their appropriate storage -Test Reagent lot variation -Test Calibration variation -Random Instrumental malfunction
Post-Analytical Variables – Solutions Data entry errors Oral miscommunication of results Electronic medical errors Failure to communicate critical values POST ANALYTICAL VARIATION
Total Test Variation Biologic parameter Total Test Variation % Sodium1.9 Potassium7.1 Chloride3.8 Calcium3.2 Creatinine14.5 Uric acid11.5 Total protein4.8 Albumin5.5 AST25 ALT56 ALK PO420 LDH16 Cholesterol14.8 A study on 21 subjects with serial testing on routine biochemistry analytes with samples drawn three times in a day & analysed for preanalytical, analytical & post-analytical variations. Ref –Textbook of clinical chemistry,Teitz, pg 58-60
Case studies Case 1: A Child with an Isolated Elevation in Alkaline Phosphatase (AP) A 4-year-old child has a serum AP of 1150 U/L,serum phosphate of 5.0 mg/dL and serum gamma-glutamyltransferase (GGT) of 30 U/L. The physical examination of the child is unremarkable except for a painful bruise on the right leg. On investigation - The serum was visibly hemolyzed owing to difficulty in obtaining the specimen. Case 2: An Asymptomatic Woman with Hypercalcemia An asymptomatic 65-year-old woman on a routine physical examination is noted to have the following abnormalities in her biochemical profile: Serum calcium = 11.3 mg/dL Serum phosphorous = 2.9 mg/dL Serum sodium = 140 mEq/L Serum potassium = 4.0 mEq/L Serum chloride = 112 mEq/L Serum bicarbonate = 16 mEq/L On investigation – the blood collection time exceeded one minute & touniquette used
Case studies Common problem is with an isolated elevation in a laboratory test – Whether it represents a true- or a false-positive result? The latter being more likely owing to the low prevalence of disease in ambulatory patients. Although most clinicians repeat the test when there is doubt about its validity. An alternative approaches are – 1. Recall that the reference intervals for the majority of laboratory tests are based on 2 SD from the mean of the test. Recalculate what the reference interval of the test would be using 3 rather than 2 standard deviations (SD) from the mean of the test. eg. The mean of the serum ALT is 14 U/L (normal, 8-20 U/ L), hence 2 SD is 6 U/L and 1 SD is 3 U/L. Since 3 SD encompasses 99% of the normal population, the upper limit of the ALT reference interval for 3 SD is 23 U/L (14 + 9). 2. Correlating with other associated tests 3. Using updated medical guidelines for result interpretation.
CONCLUSION- - When confronted with an unexpected differing test result, clinicians should take into consideration these intraindividual biologic, preanalytical & analytical variations before interpreting them. - Awareness & recognition by the clinician of these variations in an individual, which contribute in the total test variation would go a long way in a better health care management of the patients.
REFERENCES – REFERENCES – * 1. Clinical Diagnosis & Management by Laboratory Methods ; Todd & Sanford, Henry XX Edition. * 2. Teitz Textbook of Clinical Chemistry ; III Edition. *3. Interpretation of Diagnostic Tests ; Jaques Wallach, VI Edition. * 4. New in vitro analytical approches for clinical chemistry measurements in critical care ;Clin. Chem. 1990 Aug; 36(8 pt 2) : 1567 - 72 * 5. What do unexpected Results mean ? ;Postgrad. Med. 2000 June; 107(7); 145-162.
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