The sodium, potassium, and CO2 are measured by ion selective electrodes. The chloride is measured by the ferric thiocyanate method. Upon reviewing the results, the medical technologist performs a quick written calculation and decides that the specimen should be re-analyzed, believing that the results are unusual.
Which of the above results seem unusual? The chloride result is in the high abnormal range and seems unusual since the other electrolyte results are within the normal range. The glucose result is elevated, but not strikingly so.
What other results can be calculated from these data? Anion GAP Calculate the anion gap Anion gap = (Na+) - (Cl-) - (C02) = = +1
What are some possible causes of the low anion gap? (Na + K) – (Cl+ CO 2) (10 -20) Or Na – (Cl +CO 2) (8-16) Difference between unmeasured anions and unmeasured cations Increased Renal failure, diabetic acidosis, lactic acidosis, drugs or toxins or lab error Decreased QC Check Can’t be a negative number Analytical error, such as false elevated Cl or low Na Due to Lipemia
What are possible positive interferences in the ferric thiocyanate method for chloride? Lipemia of the sample is a common source of interference. In addition to lipemia, the presence of bromide ions (bromism) is an important source of positive interference. Present in many drugs, bromide causes a positive interference not only by reacting in the ferric thiocyanate reaction, but by producing more color on a molar basis than do chloride ions.