An older adult client with symptoms of osteoarthritis asks the nurse which form of exercise would be most beneficial. Which is the best response by the nurse?

Choice A reason: Potassium 4.7 mEq/L (4.70 mmol/L) is within the normal reference range of 3.5 to 5 mEq/L (3.5 to 5 mmol/L). Potassium is an electrolyte that helps regulate the balance of fluids and acids in the body, as well as the function of nerves and muscles. A high potassium level (hyperkalemia) can cause muscle weakness, irregular heartbeat, and cardiac arrest. A low potassium level (hypokalemia) can cause muscle cramps, fatigue, and arrhythmias.

Choice B reason: Magnesium 2.1 mEq/L (0.86 mmol/L) is within the normal reference range of 1.3 to 2.1 mEq/L (0.65 to 1.05 mmol/L). Magnesium is an electrolyte that helps regulate the activity of enzymes, muscles, and nerves, as well as the balance of calcium and potassium in the body. A high magnesium level (hypermagnesemia) can cause nausea, vomiting, flushing, muscle weakness, and respiratory depression. A low magnesium level (hypomagnesemia) can cause muscle twitching, tremors, seizures, and cardiac arrhythmias.

Choice C reason: Calcium 6.5 mg/dL (1.63 mmol/L) is below the normal reference range of 9 to 10.5 mg/dL (2.3 to 2.6 mmol/L). Calcium is an electrolyte that helps regulate the function of muscles, nerves, bones, and blood clotting. A high calcium level (hypercalcemia) can cause nausea, vomiting, constipation, confusion, kidney stones, and bone pain. A low calcium level (hypocalcemia) can cause muscle spasms, cramps, tingling, numbness, and stridor (a high-pitched sound when breathing). **This is a critical value that should be immediately reported to the healthcare provider**, as it can indicate a serious condition such as acute pancreatitis, sepsis, or massive blood transfusion.

Choice D reason: Sodium 135 mEq/L (135 mmol/L) is slightly below the normal reference range of 136 to 145 mEq/L (136 to 145 mmol/L). Sodium is an electrolyte that helps regulate the balance of fluids and acids in the body, as well as the function of nerves and muscles. A high sodium level (hypernatremia) can cause thirst, dry mouth, confusion, seizures, and coma. A low sodium level (hyponatremia) can cause headache, nausea, vomiting, fatigue, muscle weakness, and confusion.

Choice A reason: The humoral immune response is mediated by B cells that produce antibodies against specific antigens. However, this response is not the main problem in AIDS, because B cells are not directly affected by the human immunodeficiency virus (HIV) that causes AIDS. Therefore, this choice is incorrect.

Choice B reason: The cellular immune response is mediated by T lymphocytes that activate other immune cells, such as macrophages, to destroy infected or abnormal cells. This response is the main problem in AIDS, because HIV infects and destroys CD4+ T cells, which are essential for coordinating the cellular immunity. As a result, the client becomes susceptible to opportunistic infections, such as Pneumocystis jiroveci pneumonia. Therefore, this choice is correct.

Choice C reason: Bone marrow suppression of white blood cells can cause immunodeficiency, but it is not the primary cause of AIDS. Bone marrow suppression can occur as a side effect of some drugs or treatments, such as chemotherapy or radiation therapy, but it is not directly caused by HIV. Therefore, this choice is incorrect.

Choice D reason: Exposure to multiple environmental infectious agents can challenge the immune system, but it does not necessarily cause it to fail. The immune system can adapt and respond to different pathogens, unless it is compromised by an underlying condition, such as AIDS. Therefore, this choice is incorrect.