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                                                                    EXHIBIT 3.83

                                     BY LAWS

                                       OF

                 DIAGNOSTIC PATHOLOGY MANAGEMENT SERVICES, INC.

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                                      INDEX
<Table>
<Caption>
ARTICLE                               TOPIC                                       PAGE
- -------                               -----                                       ----
                                                                            
I        Offices                                                                   1
II       Meetings of Shareholders                                                  1
III      Directors                                                                 3
IV       Notices                                                                   5
V        Officers                                                                  6
VI       Certificates of Stock, Transfers of Stock,
          Closing of Transfer Books and Registered Shareholders                    8
VII      General Provisions                                                        9
VIII     Indemnification of Officers, Directors, Employees and Agents             10
IX       Amendments                                                               11
</Table>

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                                     BY LAWS

                                       OF

                 DIAGNOSTIC PATHOLOGY MANAGEMENT SERVICES, INC.

                                    ARTICLE I

                                     OFFICES

     Section 1. The registered office shall be at 1400 North Shartel, in the
City of Oklahoma City, County of Oklahoma, State of Oklahoma 73103.

     Section 2. The corporation may also have offices at such other places both
within and without the State of Oklahoma as the Board of Directors may from time
to time determine or the business of the corporation may require.

                                   ARTICLE II

                            MEETINGS OF SHAREHOLDERS

     Section 1. Meetings of shareholders for any purpose may be held at such
time and place, within or without the State of Oklahoma, as shall be stated in
the notice of the meeting or in a duly executed waiver of notice thereof.

     Section 2. Annual meetings of shareholders, commencing with the year 1993,
shall be held on the first Monday in the month of June, if not a legal holiday,
and if a legal holiday, then on the next secular day following, at Ten O'clock
A. M., at which time they shall elect by a plurality vote by written ballot a
Board of Directors, and transact such other business as may be properly brought
before the meeting.

     Section 3. Written notice of the annual meeting, stating the place, date
and hour of such meeting, shall be given to each shareholder entitled to vote
thereat not less than ten (10) days nor more than sixty (60) days before the
date of the meeting unless otherwise required by law.

     Section 4. The officer who has charge of the stock ledger of the
corporation shall prepare and make, at least ten (10) days before every meeting
of shareholders, a complete list of the shareholders entitled to vote at the
meeting, arranged in alphabetical order, showing the address of and the number
of shares registered in the name of each shareholder. Such list shall be open to
the examination of any shareholder, for any purpose germane to the meeting,
during ordinary business hours, for a period of at least ten (10) days prior to
the election, either at a place within the city where the meeting is to be held
and which place shall be specified in the notice of the meeting, or, if not
specified, at

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the place where the meeting is to be held, and the list shall be produced and
kept at the time and place of the meeting during the whole time thereof, and
subject to the inspection of any shareholder who may be present.

     Section 5. Special meetings of the shareholders, for any purpose or
purposes, unless otherwise prescribed by law or by the Certificate of
Incorporation, may be called by the President and shall be called by the
President or Secretary at the request in writing of a majority of the Board of
Directors, or at the request in writing of shareholders owning a majority in
amount of the entire capital stock of the corporation issued and outstanding and
entitled to vote. Such request shall state the purpose or purposes of the
proposed meeting.

     Section 6. Written notice of a special meeting of shareholders, stating the
place, date, hour and the purpose or purposes thereof, shall be given to each
shareholder entitled to vote thereat, not less than ten (10) days before the
date fixed for the meeting unless otherwise required by law.

     Section 7. Business transacted at any special meeting of the shareholders
shall be limited to the purposes stated in the notice.

     Section 8. The holders of a majority of the shares of stock issued and
outstanding and entitled to vote thereat, present in person or represented by
proxy, shall constitute a quorum at all meetings of the shareholders for the
transaction of business except as otherwise provided by law or by the
Certificate of Incorporation. If, however, such quorum shall not be present or
represented at any meeting of the shareholders, the shareholders entitled to
vote thereat, present in person or represented by proxy, shall have power to
adjourn the meeting from time to time, without notice other than announcement at
the meeting, until a quorum shall be present or represented; provided, however,
that if the date of any adjourned meeting is more than thirty (30) days after
the date for which the meeting was originally noticed, or if a new record date
is fixed for the adjourned meeting, written notice of the place, date and hour
of the adjourned meeting shall be given in conformity herewith. At such
adjourned meeting at which a quorum shall be present or represented, any
business may be transacted at the meeting as originally notified.

     Section 9. When a quorum is present at any meeting, the affirmative vote of
the holders of a majority of the shares of stock having voting power present in
person or represented by proxy shall decide any question brought before such
meeting, unless the question is one upon which, by express provision of law or
of the Certificate of Incorporation, a different vote is required, in which case
such express provision shall govern and control the decision of such question.

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     Section 10. Each shareholder shall at every meeting of the shareholders be
entitled to one vote in person or by proxy for each share of the capital stock
having voting power held by such shareholders, but NO proxy shall be voted or
acted upon after three (3) years from its date unless the proxy provides for a
longer period, and except where the transfer books of the corporation have been
closed or a date has been fixed as a record date for the determination of its
shareholders entitled to vote, no share of stock shall be voted on at any
election for directors which has been transferred on the books of the
corporation within twenty (20) days preceding such election of directors.

     Section 11. Any action required to or which may be taken at any annual or
special meeting of the shareholders, may be taken without a meeting, without
prior notice and without a vote, if a consent in writing, setting forth the
action, so taken, shall be signed by the holders of outstanding stock having not
less than the minimum number of votes that would be necessary to authorize or
take such action at a meeting at which all shares entitled to vote thereon were
present and voted. Prompt notice of the taking of the corporate action by the
shareholders without a meeting by less than unanimous written consent shall be
given to those shareholders who have not consented in writing.

                                   ARTICLE III

                                    DIRECTORS

     Section 1. The number of directors which shall constitute the whole Board
shall be not less than two (2) nor more than seven (7). As of May 4, 1992, the
Board shall consist of two (2) directors. Thereafter, within the limits above
specified, the number of directors shall be determined by resolution of the
Board of Directors or by the shareholders at the annual or a special meeting of
the shareholders. Except for the election held by the incorporator (s) and
except as provided in Section 2 and in Section 14 of this Article III, the
directors shall be elected at the annual meeting of shareholders. Each director
elected shall hold office until such director's successor is elected and
qualified, or until such director's earlier resignation or removal. Directors
need not be shareholders.

     Section 2. Except as provided in Section 14 of this Article III, vacancies
and newly created directorships resulting from any increase in the authorized
number of directors by the directors may be filled by a majority of the
directors then in office, though less than a quorum, and any director so chosen
shall hold office until the next annual election and until such director's
successor is duly elected and shall qualify, unless such director resigns or is
removed.

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     Section 3. The business of the corporation shall be managed by its Board of
Directors which may exercise all such powers of the corporation and do all such
lawful acts and things as are not by law or by the Certificate of Incorporation
or by these By Laws directed or required to be exercised or done by the
shareholders.

     Section 4. The Board of Directors of the corporation may hold meetings,
both regular and special, either within or without the State of Oklahoma.

     Section 5. Regular meetings of the Board of Directors may be held at such
time and at such place as shall from time to time be determined by the Board.
Five (5) days' notice of all regular meetings shall be given, and such notice
shall state the place, date, hour and the business to be transacted at and
purpose of such meeting.

     Section 6. Special meetings of the Board may be called by the President, on
three (3) days' notice to each director either personally or by mail or by
telegram. Special meetings shall be called by the President or Secretary in like
manner and on like notice on the written request of two (2) directors unless the
corporation has at that time less than three (3) directors, in which latter
event the request of only one (1) director shall be required. Notice of any
special meeting shall state the place, date, hour and the business to be
transacted at and the purpose of such meeting.

     Section 7. At all meetings of the Board, a majority of the directors shall
constitute a quorum for the transaction of business, and the act of a majority
of the directors present at any meeting at which there is a quorum shall be the
act of the Board of Directors, except as may be otherwise specifically provided
by law or by the Certificate of Incorporation. If a quorum shall not be present
at any meeting of the Board of Directors, the directors present thereat may
adjourn the meeting from time to time, without notice other than announcement at
the meeting, until a quorum shall be present.

     Section 8. The Board of Directors may, by resolution, passed by a majority
of the whole Board, designate one or more committees, each committee to consist
of one (1) or more of the directors of the corporation, which, to the extent
provided in the resolution, shall have and may exercise the powers of the Board
of Directors in the management of the business and affairs of the corporation
and may authorize the seal of the corporation to be affixed to all papers which
may require it. Such committee or committees shall have such name or names as
may be determined from time to time by resolution adopted by the Board of
Directors.

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     Section 9. Each committee shall keep regular minutes of its meetings and
report the same to the Board of Directors when required.

     Section 10. Members of the Board of Directors, or of any committee thereof,
may participate in a meeting of such Board or committee by means of conference
telephone or similar communications equipment that enables all persons
participating in the meeting to hear each other. Such participation shall
constitute presence in person at such meeting.

     Section 11. Unless otherwise restricted by the Certificate of Incorporation
or these Bylaws, any action required or permitted to be taken at any meeting of
the Board of Directors or of any committee thereof may be taken without a
meeting, if a written consent to such action is signed by all members of the
Board or of such committee as the case may be, and such written consent is filed
with the minutes of proceedings of the Board or committee.

     Section 12. The directors may be paid their expenses, if any, of attendance
at such meeting of the Board of Directors and may be paid a fixed sum for
attendance at such meeting of the Board of Directors or a stated salary as
director. No such payment shall preclude any director from serving the
corporation in any other capacity and receiving compensation therefor. Members
of special or standing committees may be allowed like compensation for attending
committee meetings.

     Section 13. The Board of Directors at any time may, by affirmative vote of
a majority of the members of the Board then in office, remove any officer
elected or appointed by the Board of Directors for cause or without cause.

     Section 14. Any director may be removed, for cause or without cause, by a
majority vote of the shareholders entitled to vote for the election of such
director at any annual or special meeting of the shareholders. Upon such removal
of a director, the shareholders (and not the remaining directors) shall elect a
director to replace such removed director at the same shareholders' meeting at
which such removal took place or at a subsequent shareholders' meeting.

                                   ARTICLE IV

                                     NOTICES

     Section 1.Notice to directors and shareholders shall be in writing and
delivered personally or mailed to the directors or shareholders at their
addresses appearing on the books of the corporation. Notice by mail shall be
deemed to be given at the time when the same shall be deposited in the United
States mail, postage prepaid. Notice to directors may also be given by

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telegram. Notice by telegram shall be deemed to be given when delivered to the
sending telegraph office.

     Section 2. Whenever any notice is required to be given under the provisions
of law or of the Certificate of Incorporation or of these Bylaws, a waiver
thereof in writing, signed by the person or persons entitled to such notice,
whether before or after the time stated therein, shall be deemed equivalent to
notice.

                                    ARTICLE V

                                    OFFICERS

     Section 1. The officers of the corporation shall be chosen by the Board of
Directors and shall, at a minimum, consist of a President and a Secretary. The
Board of Directors may also choose additional officers, including a Chairman or
Vice-Chairman of the Board of Directors, one or more Vice-Presidents who may be
classified by their specific function, a Secretary, a Treasurer and one or more
Assistant Secretaries and Assistant Treasurers. Two or more offices may be held
by the same person, except the offices of President and Secretary.

     Section 2. The Board of Directors at its first meeting and after each
annual meeting of shareholders shall choose a President and a Secretary, and may
choose such other officers and agents as it shall deem necessary.

     Section 3. The salaries of all officers and agents of the corporation shall
be determined by the Board of Directors.

     Section 4. The officers of the corporation shall hold office until their
successors are chosen and qualify, or until their earlier resignation or
removal. Any vacancy occurring in any office of the corporation shall be filled
by the Board of Directors.

     Section 5. The Chairman, or, in the absence of the Chairman, a
Vice-chairman of the Board of Directors, if chosen, shall preside at all
meetings of the Board of Directors, and shall perform such other duties and have
such other powers as the Board of Directors may from time to time prescribe.

     Section 6. The President shall be the chief executive officer of the
corporation, shall preside at all meetings of the shareholders and, unless a
Chairman or Vice Chairman of the Board has been chosen, at all meetings of the
Board of Directors, and shall have general and active management of the business
of the corporation and shall see that all orders and resolutions of the Board of
Directors are carried into effect.

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     Section 7. The President shall execute bonds, mortgages and other contracts
requiring a seal, under the seal of the corporation, except where required or
permitted by law to be otherwise signed and executed and except where the
signing and execution thereof shall be expressly delegated by the Board of
Directors to some other officer or agent of the corporation.

     Section 8. The Vice-President, or if there shall be more than one, the
Vice-Presidents in the order determined by the Board of Directors, shall, in the
absence or disability of the President, perform the duties and exercise the
powers of the President and shall perform such other duties and have such other
powers as the Board of Directors may from time to time prescribe.

     Section 9. The Secretary shall attend all meetings of the Board of
Directors and all meetings of the shareholders and record all the proceedings of
the meetings of the corporation and the Board of Directors in a book to be kept
for that purpose and shall perform like duties for the standing committees when
required. The Secretary shall give, or cause to be given, notice of all meetings
of the shareholders and regular and special meetings of the Board of Directors,
and shall perform such other duties as may be prescribed by the Board of
Directors or President, under whose supervision the Secretary shall be.
Additionally, the Secretary shall have custody of the corporate seal of the
corporation, and the Secretary or an Assistant Secretary, shall have authority
to affix the same to any instrument requiring it, and when so affixed. It may be
attested by the Secretary's signature or by the signature of such Assistant
Secretary. The Board of Directors may give general authority to any other
officer to affix the seal of the corporation and to attest the affixing by the
Secretary's signature.

     Section 10. The Assistant Secretary, or if there be more than one, the
Assistant Secretaries in the order determined by the Board of Directors, shall,
in the absence or disability of the Secretary, perform the duties and exercise
the powers of the Secretary and shall perform such other duties and have such
other powers as the Board of Directors from time to time prescribe.

     Section 11. The Treasurer, if one is chosen or, if not, the Secretary,
shall have the custody of the corporate funds and securities and shall keep full
and accurate accounts of receipts and disbursements in books belonging to the
corporation and shall deposit all moneys and other valuable effects in the name
and to the credit of the corporation in such depositories as may be designated
by the Board of Directors.

     Section 12. The Treasurer, if one is chosen or, if not, the Secretary,
shall disburse the funds of the corporation as may be ordered by the Board of
Directors taking proper vouchers for such disbursements, and shall render to the
President and the Board of

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Directors, at its regular meetings, or when the Board of Directors so requires,
an account of all transactions performed by the Treasurer (or Secretary, as the
case may be) and of the financial condition of the corporation.

     Section 13. If required by the Board of Directors, the Treasurer, if one is
chosen or, if not, the Secretary, shall give the corporation a bond (which shall
be renewed every six (6) years) in such sum and with such surety or sureties as
shall be satisfactory to the Board of Directors for the faithful performance of
the duties of the office of a treasurer and for the restoration to the
corporation, in case of the Treasurer's (or Secretary's, as the case may be)
death, resignation, retirement or removal from office, of all books, papers,
vouchers, money and other property of whatever kind in the possession or under
the control of the Treasurer (or Secretary, as the case may be) belonging to the
corporation.

     Section 14. The Assistant Treasurer, or if there shall be more than one,
the Assistant Treasurers in the order determined by the Board of Directors,
shall, in the absence or disability of the Treasurer, perform the duties and
exercise the powers of the Treasurer and shall perform such other duties and
have such other powers as the Board of Directors may from time to time
prescribe.

                                   ARTICLE VI

                   CERTIFICATES OF STOCK, TRANSFERS OF STOCK,
                          CLOSING OF TRANSFER BOOKS AND
                             REGISTERED SHAREHOLDERS

     Section 1. Every holder of stock in the corporation shall be entitled to
have a certificate signed by or in the name of the corporation by the Chairman
or Vice Chairman of the Board of Directors, or the President or a
Vice-President, and by the Treasurer or an Assistant Treasurer, or the Secretary
or an Assistant Secretary of the corporation, certifying the number of shares
owned by the shareholder in the corporation.

     Section 2. Any or all the signatures on the certificate may be a facsimile.
In case any officer, transfer agent or registrar who has signed or whose
facsimile signature has been placed upon a certificate shall have ceased to be
such officer, transfer agent or registrar before such certificate is issued, it
may be issued by the corporation with the same effect as if the person who
signed the certificate was such officer, transfer agent or registrar at the date
of issue.

     Section 3. The Board of Directors may direct a new certificate or
certificates to be issued in place of any certificate or certificates
theretofore issued by the corporation alleged to have been lost or stolen or
destroyed, upon the making

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of an affidavit of that fact by the person claiming the certificate of stock to
be lost, stolen or destroyed. When authorizing such issue of a new certificate
or certificates, the Board of Directors may, in its discretion and as a
condition precedent to the issuance thereof, require the owner of such lost,
stolen or destroyed certificate or certificates, or such owner's legal
representative, to advertise the same in such manner as the corporation shall
require and/or to give the corporation a bond in such sum as the corporation may
direct as indemnity against any claim that may be made against the corporation
with respect to the certificate alleged to have been lost, stolen or destroyed.

     Section 4. Subject to transfer restrictions permitted by Section 1055 of
Title 18 of the Oklahoma Statutes and to stop transfer orders directed in good
faith by the corporation to any transfer agent to prevent possible violations of
federal or state securities laws, rules or regulations, upon surrender to the
corporation or the transfer agent of the corporation of a certificate for shares
duly endorsed or accompanied by proper evidence of succession, assignment or
authority to transfer, it shall be the duty of the corporation to issue a new
certificate to the person entitled thereto, cancel the old certificate and
record the transaction upon its books.

     Section 5. The Board of Directors may fix a record date, which shall not be
more than sixty (60) days nor less than ten (10) days before the date of any
meeting of shareholders, nor more than sixty (60) days prior to the time for the
other action hereinafter described, as of which there shall be determined the
shareholders who are entitled: to notice of or to vote at any meeting of
shareholders or any adjournment thereof; to express consent to corporate action
in writing without a meeting; to receive payment of any dividend or other
distribution or allotment of any rights; or to exercise any rights with respect
to any change, conversion or exchange of stock or with respect to any other
lawful action.

     Section 6. The corporation shall be entitled to treat the person in whose
name any share of stock is registered on the books of the corporation as the
owner thereof for all purposes and shall not be bound to recognize any equitable
or other claim or other interest in such shares on the part of any other person,
whether or not the corporation shall have express or other notice thereof.

                                   ARTICLE VII

                               GENERAL PROVISIONS

     Section 1. Dividends upon the capital stock of the corporation, subject to
the provisions of the Certificate of Incorporation, if any, may be declared by
the Board of Directors at any regular or special meeting, pursuant to law.
Dividends may

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be paid in cash, in property or in shares of the corporation's capital stock.

     Section 2. There may be set apart out of any of the funds of the
corporation available for dividends such amounts as the Board of Directors deems
proper as a reserve or reserves for working capital, depreciation, losses in
value, or for any other proper corporate purpose, and the Board of Directors may
increase, decrease or abolish any such reserve in the manner in which it was
created.

     Section 3. The Board of Directors shall present at each annual meeting and
at any special meeting of the shareholders when called for by a vote of the
shareholders, a full and clear statement of the business and condition of the
corporation.

     Section 4. All checks or demands for money and notes of the corporation
shall be signed by such officer or officers or such other person or persons as
the Board of Directors may from time to time designate.

     Section 5. The fiscal year of the corporation shall be determined by the
Board of Directors.

     Section 6. The Board of Directors may provide a suitable seal, containing
the name of the corporation, which seal shall be in the charge of the Secretary.
If and when so directed by the Board of Directors or a committee thereof,
duplicates of the seal may be kept and used by the Treasurer or by the Assistant
Secretary or Assistant Treasurer. The seal may be used by causing it, or a
facsimile thereof, to be impressed or affixed or in any other manner reproduced.

     Section 7. The books of account and other records of the corporation may be
kept (subject to any provisions of Oklahoma law) at the principal place of
business and chief executive office of the corporation.

                                  ARTICLE VIII

                     INDEMNIFICATION OF OFFICERS, DIRECTORS,
                              EMPLOYEES AND AGENTS

     Section 1. To the extent and in the manner permitted by the laws of the
State of Oklahoma, and specifically as is permitted under Section 1031 of Title
18 of the Oklahoma Statutes, the corporation shall indemnify any person who was
or is a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative, other than an action by or in the right of the corporation, by
reason of the fact that such person is or was a director, officer, employee or
agent of the

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corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise against expenses, including attorneys' fees,
judgments, fines and amounts paid in settlement.

                                   ARTICLE IX

                                   AMENDMENTS

     Section 1. The Bylaws may be amended or repealed, or new Bylaws may be
adopted by the shareholders or by the Board of Directors at any regular meeting
of the shareholders or of the Board of Directors, or at any special meeting of
the shareholders or of the Board of Directors if notice of such amendment,
repeal or adoption of new Bylaws be contained in the notice of such special
meeting.

     APPROVED AND RATIFIED this 4th day of May, 1992, by the undersigned,
constituting all of the directors (whether one or more) of the corporation.

                                             /s/ Tommy Lloyd Hewett
                                             ----------------------
                                             Tommy Lloyd Hewett

                                             /s/ Cheryl A. Hewett
                                             ----------------------
                                             Cheryl A. Hewett

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