<PAGE>

                                                                 EXHIBIT 10.51.1

                             CHOLESTECH CORPORATION

                     FIRST AMENDMENT TO SEVERANCE AGREEMENT

         This First Amendment to the Severance Agreement dated as of April 1,
2003 (the "Agreement"), is made as of October 10, 2003 (the "Amendment"), by and
between Cholestech Corporation, a California corporation (the "Company"), and
Don Wood (the "Employee").

         WHEREAS, the Company and the Employee desire to amend Section 2(b) of
the Agreement;

         NOW, THEREFORE, in consideration of the foregoing and the mutual
promises set forth herein, the Company and the Employee agree as follows:

         1.       Section 2(b) is hereby amended to read in its entirety as
follows:

         "Severance Payment. If the Company terminates the Executive's
employment, for any or no reason, then the Executive shall be entitled to
receive a severance payment in an amount equal to 12 months of the Executive's
base salary as in effect immediately prior to such termination. Such severance
payment shall be in lieu of any other severance payment to which the Executive
shall be entitled pursuant to any employment agreement, offer letter or the
Company's then existing severance plans and policies; provided, however, that
the Executive shall be entitled to the severance payment provided for in Section
4(b)(i) of the Change of Control Severance Agreement between the Executive and
the Company (the "Change of Control Agreement") in lieu of the severance payment
provided for under this Agreement if the Executive's employment with the Company
terminates as a result of an Involuntary Termination (as such term is defined in
the Change of Control Agreement) at any time within 12 months after a Change of
Control (as such term is defined in the Change of Control Agreement). Such
severance payment shall be payable over a period of 12 months commencing on the
date of such termination in accordance with the Company's normal payment
practices. In addition, during the 12 month period commencing on the date of
such termination, the Company shall continue to make available to the Executive
and the Executive's spouse and dependents covered under any group health plans
or life insurance plans of the Company on the date of such termination of
employment, all group health, life and other similar insurance plans in which
the Executive or such covered dependents participate on the date of the
Executive's termination; provided, however, that (i) the Executive constitutes a
qualified beneficiary, as defined in Section 4980B(g)(1) of the Internal Revenue
Code of 1986, as amended; and (ii) the Executive elects continuation coverage
pursuant to the Consolidated Omnibus Budget Reconciliation Act of 1985, as
amended ("COBRA"), within the time period prescribed pursuant to COBRA."

         2.       Except as amended as set forth above, the Agreement shall
continue in full force and effect and the parties thereto shall continue to
enjoy and be bound by all of their rights and obligations thereunder.

<PAGE>

         3.       This Amendment shall be governed by and construed in
accordance with the laws of the State of California, regardless of the laws that
might otherwise govern under applicable principles of conflicts of laws thereof.

         4.       This Amendment may be executed in one or more counterparts,
all of which shall be considered one and the same amendment, and shall become
effective when one or more counterparts have been signed by each of the parties
and delivered to the other party, it being understood that all parties need not
sign the same counterpart.

         5.       Capitalized terms not otherwise defined in this Amendment
shall have the meanings ascribed to them in the Agreement.

                  [REMAINDER OF PAGE LEFT BLANK INTENTIONALLY]

                                                                             -2-
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this First
Amendment to the Severance Agreement as of the day and year first above written.

                                    CHOLESTECH CORPORATION
                                    a California corporation

                                    By:    /s/ Warrne E. Pinckert II
                                        ----------------------------
                                           Warren E. Pinckert II
                                           President and Chief Executive Officer

                                           /s/ Don Wood
                                    -------------------------------
                                    Don Wood

                                                                             -3-