Pain classification with VAS scores ‘doubtful’

By Lucy Piper, Senior medwireNews Reporter

Researchers advise caution when using cutoff points on the visual analogue scale (VAS) to classify mild, moderate or severe pain in clinical practice.

They found that a VAS cutoff score below 3.5 was consistently associated with mild pain, but the cutoff point between moderate and severe pain was less clear and subject to misinterpretation.

Also, VAS scores were, at best, only moderately associated with functioning and with Verbal Rating Scale (VRS) scores.

“In view of the low to moderate associations, it is questionable whether it is useful in clinical practice to translate the VAS scores into mild, moderate or severe pain”, say the researchers, led by Anne Boonstra (Revalidatie Friesland Centre for Rehabilitation, Beetsterzwaag, the Netherlands).

A total of 456 patients, older than 18 years of age, with chronic musculoskeletal pain were asked to rate their pain in the preceding 4 weeks using the VAS.

Statistical analysis showed that a VAS score of up to 3.4 cm corresponded to mild interference of pain with functioning on the Short Form (SF)-36, while a score of 3.5 to 6.4 was associated with moderate interference and a score of 6.5 or above with severe interference.

A VAS score of up to 3.4 cm similarly corresponded best with mild pain on the VRS, but the score for moderate pain was 3.5 to 7.4 and for severe pain 7.5 or above.

Latent class analyses found three classes, corresponding to scores of 3.8 cm or below, 3.9 to 5.7 cm and 5.8 cm or above.

This means that a score of up to about 3.5 cm was consistent for describing mild pain across all three methods. However, the distinction between moderate and severe pain varied.

The overlap between moderate and severe VAS cutoff points in terms of pain-related interference with functioning and verbal rating mean that a patient may score their pain on VRS as moderate but its impact on functioning could be severe, the researchers explain in Pain.

They note that their findings are in agreement with some previous studies, while others have found different optimal cutoff points, suggesting a lack of consensus.

“This would also make such a classification difficult to use in practice”, Boonstra and team say, concluding: “[T]he correct classification of VAS scores as mild, moderate or severe in clinical practice seems doubtful.”

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