Three tests at the bedside — point-of-care glucose, ketone and urinalysis in a sick child

Structured clinical encounter — interpretation and procedural leadership

This station tests whether the candidate performs and interprets the three core paediatric point-of-care tests correctly, defends the blood ketone over the urine ketone with the ISPAD thresholds, applies the neonatal glucose meter limitation, and leads the dipstick-to-culture approach in the febrile non-toilet-trained infant. Marks reward the test chemistry, the confirmation rule, the ISPAD thresholds, and the falsely reassuring results. [1]

Stem

A seven-year-old with known type 1 diabetes arrives in the emergency department vomiting and breathless, with deep sighing respirations and the smell of ketones. The bedside glucose meter reads 23 mmol per litre, the blood beta-hydroxybutyrate is 4.8 mmol per litre and the venous pH is 7.14. In the next bay, a febrile nine-month-old has a urine dipstick positive for the leukocyte esterase and negative for the nitrite, collected by the adhesive bag. The team looks to you for the interpretation of the three bedside tests and the next steps.

Candidate tasks

1. Interpret the glucose meter and the blood ketone aloud (3 minutes). State the glucose meter strip chemistry, why the blood beta-hydroxybutyrate is preferred over the urine acetoacetate, and the ISPAD diagnostic thresholds that confirm the diabetic ketoacidosis. [1] [8]
2. Apply the neonatal glucose meter limitation (2 minutes). Explain why a capillary glucose in a neonate must be confirmed by the laboratory plasma glucose, naming the high haematocrit, the oxygen, and the galactose or maltose interference with the glucose dehydrogenase pyrroloquinoline-quinone strips. [6]
3. Interpret the urine dipstick in the febrile infant (3 minutes). State the leukocyte esterase and the nitrite performance, the lower nitrite sensitivity in the young infant, and why the culture from the catheterisation or the suprapubic aspiration is needed before any antibiotic. [4] [10]
4. Recognise the falsely reassuring results (2 minutes). Name the lagging urine ketones during the recovery, the negative nitrite in the infant, and the euglycaemic diabetic ketoacidosis. [1] [5]
5. Communicate the results and the plan to the family (2 minutes). Frame the bedside test as the first step and the laboratory test as the confirmation, and explain the dipstick-to-culture principle in plain language. [8] [10]

Examiners' discussion points

• Why the blood ketone over the urine ketone? The beta-hydroxybutyrate is the predominant ketone, measured directly, and it falls with the insulin to track the resolution. The urine acetoacetate lags behind and can rise during the recovery as the beta-hydroxybutyrate converts to the acetoacetate, which is the source of the false reassurance. [1] [8]
• The glucose meter limitation. The high haematocrit and the galactose or maltose interference bias the neonatal reading in either direction, so the laboratory plasma glucose confirms the critical value. The whole-blood glucose reads approximately ten to twelve per cent lower than the plasma because the red cells contain less glucose, and the interference-corrected meter such as the Nova StatStrip gives the better accuracy in the neonatal intensive care. [6]
• The nitrite in the infant. The Griess reaction needs the bladder dwell time for the nitrate conversion, and the young infant voids frequently, so the nitrite sensitivity falls to approximately fifty per cent even though the specificity stays high at approximately ninety-eight per cent. The combined both-negative dipstick carries the high negative predictive value, but it does not rest on the nitrite alone. [4] [5]
• The dipstick-to-culture principle. The febrile non-toilet-trained child obtains the culture from the catheterisation or the suprapubic aspiration before any antibiotic, because the adhesive bag specimen is unsuitable for the culture, and the dipstick is a screen that the culture confirms. [2] [10]

Marking grid (out of 20)