celeste
Try the Medicare Claims Processing Manual, excerpts follow:
Medicare Claims Processing Manual
Chapter 26 - Completing and Processing
Form CMS-1500 Data Set
(Rev. 2162, 02-22-11)
10.4 - Items 14-33 - Provider of Service or Supplier Information
Item 21 - Enter the patient's diagnosis/condition. With the exception of claims submitted by ambulance suppliers (specialty type 59), all physician and nonphysician specialties (i.e., PA, NP, CNS, CRNA) use an ICD-9-CM code number and code to the highest level of specificity for the date of service. Enter up to four diagnoses in priority order. All narrative diagnoses for nonphysician specialties shall be submitted on an attachment
10.1 – Claims That are Incomplete or Contain Invalid Information
(Rev. 145, 04-23-04)
If a claim is submitted with incomplete or invalid information, it may be returned to the submitter as unprocessable. See Chapter 1 for definitions and instructions concerning the handling of incomplete or invalid claims.
10 - Health Insurance Claim Form CMS-1500 (Rev. 2162, Issued: 02-22-11, Effective: 03-21-11, Implementation: 03-21-11)
The current version of the form is Form CMS-1500 (08/05) and is approved under the OMB collection 0938-0999. The Form CMS-1500 (Health Insurance Claim Form) is sometimes referred to as the AMA (American Medical Association) form. The Form CMS-1500 is the prescribed form for claims prepared and submitted by physicians or suppliers, whether or not the claims are assigned.
The Form CMS-1500 answers the needs of many health insurers. It is the basic form prescribed by CMS for the Medicare and Medicaid programs for claims from physicians and suppliers. It has also been adopted by the TRICARE Program and has received the approval of the American Medical Association (AMA) Council on Medical Services.
(End Quote)
Hope this helps.