A study on effect of lipemia on electrolyte measurement by Direct Ion- Selective Electrode method. Dr. Susruta Sen MD, DNB, PG Dip. Diabetology Consultant Dept of Lab Medicine The Calcutta Medical Research Institute

O Assess renal, endocrine, water balance and acid-base function O Diagnosis and management of Cushing’s and Addison’s disease O Potassium levels are indicated in tachycardia, arrhythmia, cardiac arrest etc. O Comprise approx % of routine chemistry tests in any lab O The Laboratory must have the ability to perform these assys quickly & reliably Clinical utility of electrolyte measurement

O Direct ISE O No dilution of sample prior to analysis O Fixed electrodes with semi-permeable membranes requiring more frequent replacement (except VITROS slides with disposable electrodes) O Direct methods measure only the free ion giving a more physiologically correct result. O Indirect ISE O Pre-dilution of sample prior to analysis O Artifacts or erroneous results in samples containing high lipids and proteins O In Direct method measure not only the free but also the bound & complexed ions. Methods of Electrolyte Measurement

Direct Vs Indirect ISE

Electrolyte Exclusion Effect O Both direct & indirect methods produce comparable and accurate results O Indirect - dilutions are based on this “fixed” 93,7 ratio to calculate patient values Normal patient sample 93% 7% Aqueous Solution (Serum) Non-aqueous Solution (Lipids, Proteins) Na+ Abnormal patient sample Less than 93% Greater than 7% Aqueous Solution (Serum) Non-aqueous Solution (Lipids, Proteins) Na+ Indirect methods may underestimate “true” sodium concentrations since the aqueous solution is decreased due to higher than normal lipid or protein concentrations

Abnormal Lipids Patients with variety of diseases will have O Increase Lipids O Glycogen Storage diseases O Dyslipidemia O Diabetes – 30 Million diabetics in India O Acute pancreatitis O Hypothyroidism ………..

Indirect ISEs Have Been Problematic for a Long Time (References) O Rapid measurement of serum water to assess pseudohyponatremia O Clin Chem 32: O Pseudohyponatremia: a reappraisal O RWJ Med School “can lead to dangerous errors in patient management” O The hyponatremic patient: A systemic approach to lab Diagnosis O CMAJ (2002):166:1056 O Jan Effects of hyperlipidemia on Na, K, CL… By indirect ISE Measuring System O Clin Chem Letter to the Editor O Roche Modular - “hyperlipidemia caused errors in indirect electrolyte measurement O Poster on Electrolyte Study, Apollo Ludhiana

O Indirect ISEs are prone to pseudohyponatermia O Falsely low sodium results due to high lipids and proteins O Potential Medical Error O Many patients with high lipids and proteins O Lots of patients receiving IVs with lipid infusions O Prone to pseudohyponatermia O Avoid potential medical error by utilizing Direct ISEs Avoid potential medical errors

Objectives O To observe whether lipemia affects the measurement of electrolytes using direct potentiometry by increasing concentration of triglyceride on the serum samples in vitro. O To find out (if it affects) the specific concentration at which the effect starts making significant difference in measurement of electrolytes in the study subjects.

Methods O Type of study: Laboratory based experimental design. O Study population: subjects admitted in IPD of a tertiary care hospital, Kolkata, WB, India. O Study duration: 3 months, June-August,2014 O Sampling: 120 consecutive serum samples

Tools used 1. Clot/red capped vials. 2. Laboratory centrifuge model REMI R-8C. 3. Micro centrifuge tubes 4. Micropipette 5. INTRALIPID® 10%: a sterile fat emulsion containing soya oil, egg lecithin and glycerol. 6. HDC LYTE Electrolyte analyzer. 7. Vitros 250 Chemistry Analyzer

Methods contd… Each serum sample: A set of five:- Neat, Neat+5µl, Neat+10µl, Neat+15µl, Neat+20µl, Electrolytes measured in differents slots in the Vitros 250 Dry Chemistry Analyzer and HDC Lyte machines Data anlysed after categorizing in three groups: Hypo/Normo/Hyper natremia

Results O Comparison between electrolyte values obtained from two different equipments. O Comparison of electrolyte values at different concentration of triglyceride. O Assessing the drift of electrolyte results with a focus on clinical significance.

O :Considered as the baseline concentration of IL. O Values obtained in different concentration was digitized. O Compared with baseline concentration by Paired t test. O Independent t test was also used to estimated the difference between values obtained from two equipments in similar concentration.

St atistically significant difference compared to baseline of TG mg/dl concentration, measuring Na+ Vitros-250HDC-Lyte Natremia HypoNormoHyperHypoNormoHyper >

Statistically significant difference compared to baseline of TG mg/dl concentration, measuring K + Vitros-250HDC-Lyte Natremia HypoNormoHyperHypoNormoHyper >

Comparing the two instruments Triglyceride conecntration (mg/dl) N Mean (mmol/Lt) Std. Deviation Std. Error Meanp-value Na Vitros HDC-Lyte K Vitros HDC-Lyte Na Vitros HDC-Lyte K Vitros HDC-Lyte Na Vitros HDC-Lyte K Vitros HDC-Lyte Na Vitros HDC-Lyte K Vitros HDC-Lyte Na+>1550 Vitros HDC-Lyte K+>1550 Vitros HDC-Lyte

Hypernatremic sample Comparision TriglycerideNA+(Vitros)NA+(HD Lyte) > Triglyceride Na% diff(Vitros)Na% diff(HD Lyte) >

Hypernatremic Samples Comparision for K+ TriglycerideK+(Vitros)K+(HD Lyte) > Triglyceride K% diff(Vitros)K% diff(HD Lyte) >

Normonatremic Sample Comparision TriglycerideNA+(Vitros)NA+(HD Lyte) > Triglyceride Na% diff(Vitros)Na% diff(HD Lyte) >

Normonatremic Samples Comparision for K+ TriglycerideK+(Vitros)K+(HD Lyte) > Triglyceride K% diff(Vitros)K% diff(HD Lyte) >

Hyponatremic Sample Comparision TriglycerideNA+(Vitros)NA+(HD Lyte) > Triglyceride Na% diff(Vitros)Na% diff(HD Lyte) >

Hyponatremic Samples comparision for K+ TriglycerideK+(Vitros)K+(HD Lyte) > Triglyceride K% diff(Vitros)K% diff(HD Lyte) >

Conclusion O The two instruments are mostly comparable for measuring electrolyte concentration. O However, O Vitros 250 appears to be more consistent with Na+ concentration result compared to HDC lyte in different lipemic state. O Beyond 1550 mg/dl concentration of TG, the difference between electrolyte concentration measured in two instruments varied significantly.

Conclusion O The results showed statistically significant difference between electrolyte concentration measured in both instruments at mg/dl TG concentration and gradually escalated lipemic states, except: O (Lipemia mg/dl) O HDC lyte : Na+ & K+ in hypernatremic group O Vitros250: Na+ in hypo & normonatremic groups

Conclusion O Clinically significant drift noted in:  >1050 mg/dl of TG concentration for HDC lyte  >1550 mg/dl of TG concentration for both the instruments.

Conclusion O Further studies required to establish a correction factor for measuring electrolyte concentration in regular patient care setting for lipemic samples. O To find out the optimum TG concentration till which the electrolyte results remains unaffected if measured by direct ISE method.

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