Problem of measurement of potassium level in newborn due to the interference of ammonia.

Sir,

The measurement of blood electrolytes is a basic step in determining the metabolic status of a patient. Here, the author presents and discusses an interesting. The case is a preterm, 800 g weight neonate [Figure 1a]. This patient had an identical twin but his paired twin died at birth. The metabolic derangement was that every time he was tested for arterial blood gas by point of care automated analyzer, OPTI CCA, his potassium (K+) level was quite high.

Figure 1

(a) The case of a preterm, 800 g weight neonate. (b) The case of a preterm done by another standard automated analyzer, Roche Cobas c501 (ISE principle)

When repeated testing was done by another standard automated analyzer, Roche Cobas c501 (ISE principle) [Figure 1b], his K+ result was a little bit high.

To find out the root cause, several validations of the analyzer were done. It was confirmed that the cause of problem was not linked to instrument malfunction, because this problem occurred only in this patient but inot in others. In other cases, K+ results did not shift to high and correlated with Cobas c501. In addition, the medical scientist team also checked the basic limitation and interference on the operation manual, the samples from this patient had nothing to interfere with test principle, he had no hemolysis, bilirubin 5 mg/dl, WBC 9,000/μL and the analytical medical scientist used standard blood gas capillary to collect capillary blood from patient's heel.

The root cause of aberrant result in this case study was found to be high blood ammonia. Reference to technical reports in clinical chemistry revealed that an important interference for measurement by OPTI CCA is high blood ammonia.[1] In this patient, the checking for blood ammonia was recommended and high level could be detected. Hyperammonemia is not a rare condition for the preterm; the likely causes include 1. hypoglycemia 2. transient hyperammonemia, 3. genetic metabolic disorder, 4. hyperbilirubinemia and 5. physiological immaturity.[2]