Final answer:
Capillary puncture is often used for elderly patients when their veins are fragile, there is a risk of infection from venipuncture, or only a small blood sample is needed.
Step-by-step explanation:
For elderly patients, a capillary puncture may be preferred over venipuncture in specific situations. One such situation is when the patient's veins are fragile, making venipuncture riskier due to the potential for harming the blood vessel or causing a hematoma. Another circumstance is when a patient has a history of or is currently experiencing catheter-related bloodstream infections. Capillary puncture, which requires only a small amount of blood, minimizes the risk of further infection. Lastly, capillary puncture may be chosen when only a small volume of blood is needed for laboratory analysis and the lower pressure in capillaries is sufficient for obtaining the necessary sample.