Yes, there are other endogenous and exogenous controls that can be used for the expression analysis of miRNA in patient serum samples by Q-PCR.

Endogenous controls:

1. miR-16 and let-7a are indeed commonly used as endogenous controls for blood and serum samples, as you mentioned.

2. Other commonly used endogenous controls include miR-103, miR-107, and miR-451. These miRNAs are known to have stable expression levels in human blood and serum samples.

3. Additionally, U6 small nuclear RNA (U6 snRNA) is sometimes used as an endogenous control for normalization.

Exogenous controls:

1. Cel-miR-39 is often used as an exogenous spike-in control, as you mentioned.

2. Other commonly used exogenous controls include miR-122, which is a liver-specific miRNA, and miR-23a, which has been reported to have stable expression levels across different tissues.

3. RNU6B, a small nuclear RNA, is also used as an exogenous control for normalization.

It is important to note that the choice of endogenous and exogenous controls depends on the research question and the specific sample type, and multiple controls are often used to ensure robust normalization. It is always a good idea to validate the expression levels of the controls you choose for your specific experiment.

The following link may help you find your answer; https://www.researchgate.net/post/Why_is_U6_snRNA_used_as_control_for_qPCR_for_miRNA