Final answer:
The effective use of TPN is indicated by a prealbumin level of 30 mg/dl, which shows proper nutritional support, while other listed lab values are either not directly related to TPN efficacy or suggest potential deficiencies.
Step-by-step explanation:
A nurse assessing the efficacy of total parenteral nutrition (TPN) therapy will look for laboratory values that indicate the patient's nutritional and metabolic balance. The correct answer is c. Prealbumin 30, as prealbumin is a marker for nutritional status, and a level of 30 mg/dl indicates a good response to TPN, suggesting that the patient is receiving adequate protein and calories. Normal blood calcium levels range from 9.5-10.5 mg/100 ml, so a calcium level of 8 mg/dl (option a) could indicate hypocalcemia, which is not a desired outcome. Haemoglobin levels should ideally be higher than 9 g/dL for adults, and a value of 9 indicates possible mild anaemia, also not indicative of effective TPN therapy. A cholesterol level of 140 mg/dl (option d) is within the normal range, but it is not a direct indicator of TPN effectiveness.