Final answer:
The nurse should immediately check the client's last pulse rate and notify the healthcare provider if the pulse is abnormal or signs of toxicity, as a serum digoxin level of 2.4 ng/mL may indicate digoxin toxicity.
Step-by-step explanation:
If a nurse notes a serum digoxin level of 2.4 ng/mL, the immediate action should be to check the client's last pulse rate. This is because a digoxin level above 2 ng/mL may indicate digoxin toxicity, which can lead to serious cardiac complications. Monitoring the patient's vital signs, particularly their heart rate, is crucial for assessing their stability and response to the medication. If the pulse is abnormal or if there are any signs of toxicity, the nurse should then notify the healthcare provider promptly. Recording a normal value on the client's flow sheet or administering another dose would be inappropriate without first assessing the patient and consulting with a healthcare provider.