Guidelines for Determining the Appropriate Diagnosis Code

11. Y codes used for explanations of the causes or morbidity should not be used as the first code on a claim but rather used as informative for the presenting diagnosis. 

12. Coding for adverse effects, poisoning, underdosing and toxic effects are listed in the T36-T65 categories and are combination codes that include the substance that was taken as well as the intent. No additional external cause codes are required for poisonings, toxic effects, adverse effects and underdosing codes. The codes should be selected from the tabular section and not from the Table of Drugs. There may be a need to use more than one code if multiple medications or biological substances have been used. The definitions below are the different subcategories and how to code from these subcategories:

i. Adverse effects – A drug that has been correctly prescribed and properly administered: Assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug. (T36-T50). The code for the drug should have a fifth or sixth character and may need an “x” placeholder to be able to assign a fifth or sixth character. 

ii. Poisoning – A medication has been used improperly, such as an overdose, wrong substance given, taken in error, or a wrong route of administration. If there is also a diagnosis of abuse or dependence of the substance, the abuse or dependence is assigned as an additional code.

iii. Underdosing – A medication is taken less than as prescribed. Codes from this section should never be assigned as the primary diagnosis codes. If a patient has a relapse or exacerbation of the medical condition for which the drug is prescribed because of the reduction in the dose, the medical condition itself should be coded as the primary diagnosis code. Noncompliance and/or complication of care codes are to be used with an underdosing code if indicated and known. 

iv. Toxic effect – When a harmful substance is ingested or comes in contact with a person, this is classified as a toxic effect. The toxic effect codes are in categories T51-T65. 

a. For all of the codes in the adverse effects, poisoning, underdosing and toxic effects chapter , there is a requirement to add an additional character to the code for the associated intent. The associated intent is coded as the sixth character of the code in most subsections. The sixth character choices are: i. 1 – accidental 

ii. 2 – intentional self harm

iii. 3 – assault 

iv. 4. – undetermined

b. The last requirement for these codes to be complete is the additional information regarding the encounter for adverse effect, poisoning, underdosing and toxic effects. The seventh character selections are:

i. A – Initial encounter – The patient is receiving active treatment for the condition. An example would be the initial evaluation and treatment for the patient or the evaluation and treatment by a new physician. 

ii. D – Subsequent encounter – The patient has received active treatment of the condition and is receiving routine care for the condition during the healing or recovery phase. Examples would be medication adjustments or other follow up visits following initial treatment. 

iii. S – Sequela – This is used for complications or condition that arise as a direct result of a condition. This would not be a common seventh character for the allergist to be using. However, an example of this would be if a patient is given an antibiotic by you for an infection, and subsequently develops chronic diarrhea from that antibiotic, or osteopenia secondary to chronic steroid use.

In summary, diagnosis codes need to support the services rendered. As of 2014, the electronic formats and the CMS 1500 forms are able to accept a maximum of 12 diagnosis codes per claim. The allergist will continue to use ICD-9CM codes until at least October 1, 2015. At that time, you should use the new ICD-10 CM codes and/or the ICD-9 CM codes for those payers which are not required to change to the new coding system.

It is important to link diagnosis codes to specific CPT procedure codes if multiple CPT procedure

codes are performed and reported on one calendar day. Appropriate location for the service, whether it is clinic, outpatient or hospital, is required as well for accurate claim adjudication. Diagnosis codes are the medical necessity for the patient’s evaluation. Appropriate selection of the diagnosis codes and the highest degree of specificity known for the patient at the time will support the allergist’s decision to evaluate the patient as well as obtain the appropriate reimbursement for the patient’s encounter.