One of the most important elements of healthcare services in primary care is diagnosing and determining the severity of depression. However, it is only when physicians have a high index of suspicion based on the patient’s behavioral indicators is the illness detected. As a consequence, numerous patient health history questionnaires and scales have been developed to better assess the severity of the disease. One of these patient health questionnaires is the PHQ-9.

The PHQ-9 is one of the most widely used and freely available rating scales introduced to assist clinicians in diagnosing depression, assessing the illness’s severity, and monitoring the patient’s response to treatment. This fast and relatively accurate tool was developed in 1999 and can be taken either in written form or in the form of an interview by a clinical staff. Since its inception, deployment of this self-report measure in primary care settings amongst depressive patients has become a common practice since it helps ensure a reliable diagnosis, efficacious treatment, and careful follow-up.

Purpose of the Patient Health Questionnaire PHQ-9

Depression is one of the most common illnesses around the globe. Prevalent amongst people of all ages, healthcare providers and primary care clinicians see a large number of patients with depression on a regular basis. It is often misconstrued as an untreatable illness, which is why it is one of the biggest contributors to the global burden of disease. Early detection is detrimental to the effective treatment of depression. Unfortunately, the lack of locally validated and reliable screening tools to detect depression acts as a significant hurdle in the rapid detection of this mental health disorder.

Only 46-57% of people with depression in the US receive treatment for this illness and only 18 to 25% of these patients are adequately treated. As such, the patient health questionnaire PHQ-9 proves to be a vital instrument used by physicians to diagnose depressive mental health disorders. Over the years, several studies have supported the validity and accuracy of the patient health questionnaire PHQ-9 both as a screening and a follow-up tool.

Contents of the Patient Health Questionnaire PHQ-9

The nine items on this unique patient health history questionnaire focus on the DSM-IV’s 9 diagnostic criteria for major depressive disorders. The questions on the questionnaire are based on the patient’s experience within the last two weeks regarding:

  • Their level of interest in doing things;
  • feelings of depression;
  • any trouble sleeping;
  • feelings of lethargy;
  • their appetite;
  • self-perception;
  • their concentration capabilities;
  • their functioning speed, and
  • suicidal thoughts.

Each question has to be answered on a four-point scale ranging from 0 to 3 where 0 means that the patient does not feel a certain way at all and 3 implies that they experience what is mentioned in the question nearly every day. It is important to note that patients with positive scores on the final question regarding any suicidal thoughts need to be immediately assessed further by their physician. An immediate psychiatric intervention or emergency hospitalization is necessary if the clinician feels that the patient might harm themselves.

The patient health questionnaire PHQ-9 takes approximately only two to five minutes to complete. The PHQ-9 score is obtained by adding the score for each of the nine questions, which is used to interpret the severity of depression within the patient (if any). The following are the PHQ-9 total scores and their corresponding levels of depression:

PHQ-9 Score Depression Severity
0-4 None/Minimal
5-9 Mild  
10-14 Moderate  
15-19 Moderately Severe  
20-27 Severe

There is an additional tenth question on the PHQ-9 which is not used to calculate the PHQ score and asks the patient how difficult the problems mentioned in the PHQ have made their daily activities. This question is used to help the clinician better understand the patient’s impairments due to their symptoms.

The PHQ-2 is an abridged version of the PHQ-9 which includes only the first two questions of this patient health history questionnaire. If a patient’s PHQ score is above 3 on the PHQ-2 then only is it followed by the administration of the PHQ-9.

Applications of the Patient Health Questionnaire PHQ-9

1. Initial Treatment

For practitioners, the PHQ-9 serves to help reach an objective diagnosis based on quantitative results. During the initial treatment phase, the PHQ-9 can be used to determine the best possible course of treatment – pharmacological management, psychotherapy, etc.

2. Tracking Treatment Response

Repeated administration of the test also helps clinicians track improvement or regression in the patient’s depressive state. Consistent high scores on a particular domain may identify an area that needs individualized attention and needs to be further assessed.

3. Follow-up

Depressive patients are likely to quit their treatment during the initial months which is why treatments are continued progressively in the follow-up period to prevent relapses and recurrences. During the follow-up visit, the PHQ-9 is used as an instrument to measure the patient’s response to the treatment and identify and assess which symptoms are not responding well so that the treatment can be optimized accordingly.

4. Research

Apart from facilitating the diagnosis of major depression and its intensity, the PHQ-9 is also a valuable clinical and research tool. This is majorly due to its reliability, feasibility, validity, and brevity. Valid group comparisons can also be made with this patient health history questionnaire.

Although the patient wellness questionnaire PHQ-9 has been primarily validated in primary care settings, research has shown that it is also useful for detecting depression in psychiatric clinics.

Additionally, the PHQ-9 has been adopted as a standard measure for screening depression by several organizations including the Veterans Administration and the Department of Defense. Available in over thirty languages, the test has been administered in several studies that involve patients with epilepsy, multiple sclerosis, fibromyalgia, physical disabilities, and arthritis.

Validity and Reliability

It is well established that the patient health questionnaire PHQ-9 is well documented and validated across the world. This is mainly due to its diagnostic validity and sound psychometric properties. An abundance of research is available on the psychometric properties of the PHQ-9.

One research shows that individuals who score high (≥ 10) on the PHQ-9 are between 7 to 13.6 times more likely to be diagnosed with depression by the mental health professional. On the other hand, individuals scoring low (≤ 4) on the PHQ-9 have less than a 4% chance of having depression (Source). Another research on the validity of the PHQ-9 showed that patients with a PHQ-9 score ≥10 had a sensitivity of 88% and a specificity of 88% for major depression.  This reflects that the likelihood of a false negative result is very low.


Depression remains one of the most common causes of consultation in primary care clinics yet still often remains undiagnosed and untreated. The patient health questionnaire PHQ-9 serves as a flexible and reliable instrument in diagnosing and treating depression. However, this tool can only facilitate a clinician’s decision and can never be an alternative to sound medical judgment. The limitations associated with the self-reporting of depressive symptoms are also important to consider when administering the PHQ-9.

See Also: The Role And Importance Of Big Data And Business Analytics In Healthcare

The patient health test PHQ-9 is only one of the several depression screening tools accepted by physicians across the world. Ultimately, depression management is highly dependent on patient education and their active participation in their attempt to get better.

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