Can diabetic polyneuropathy and foot ulcers in patients with type 2 diabetes be accurately identified based on ICD-10 hospital diagnoses and drug prescriptions?

Figures & data

Figure 1 Flowchart of study population. Overview of patient selection. ^aOf the 30,338 patients with potential non-painful DPN, 1826 later fulfilled the criteria for potential painful DPN. Thus, these patients are included in both the non-painful and painful DPN populations at two distinct time points. Likewise, after restricting to the Central Denmark region, 2009–2016.

Abbreviation: DPN, diabetic polyneuropathy.

Table 1 Algorithms of in- and outpatient discharge codes and prescription codes used to identify patients with painful and non-painful DPN and diabetic foot ulcer

Type 2 diabetes^a

≥1 diabetes discharge code (E10-E14, H36.6, O24 [except O24.4], G63.2)

OR

≥1 prescription of a glucose-lowering drug (ATC: A10)^b

Potential DPN:

Type 2 diabetes plus ≥1 discharge code for “diabetes with neurological complication” (E10.4, E11.4, E12.4, E13.4, E14.4)^c

OR

Type 2 diabetes plus ≥1 discharge code for “diabetic polyneuropathy” (G63.2)

OR

Type 2 diabetes plus ≥1 discharge code for “polyneuropathy, unspecified” (G62.9)

Potential painful DPN:

DPN plus ≥1 prescription code for antiepileptic drugs minus an epilepsy discharge code (G40+G41)

OR

DPN plus ≥1 prescription code for antidepressants (SNRI/TCA) minus a depression/anxiety discharge code (F30-F34, F40-42, F48.8+F48.9)

Potential non-painful DPN:

DPN patients that do not fulfil the criteria for painful DPN

Potential diabetic foot ulcer:

Type 2 diabetes plus ≥1 discharge code for “diabetes with peripheral vascular complication” (E10.5, E11.5, E12.5, E13.5, E14.5)

OR

Type 2 diabetes plus ≥1 discharge code for “ulcer” (L97, L98.4, R02)

OR

Type 2 diabetes plus ≥1 discharge code for “osteomyelitis” (M86)

OR

Type 2 diabetes plus ≥1 surgery code for surgery of lower extremity (KQDA, KQDB, KQDG)

Notes: ^aAll patients younger than 30 years at diagnosis treated with insulin monotherapy were excluded in order to minimize misclassification of type 1 diabetes patients. ^bExcept females aged 20–39 prescribed metformin exclusively in order to minimize misclassification of patients with polycystic ovarian syndrome. ^cExcluding patients with ICD-10 codes for G73.0 amyotrophy, G99.0 autonomic neuropathy, G59.0 mononeuropathy.

Abbreviations: DPN, diabetic polyneuropathy; ICD-10, International Classification of Diseases; version 10; SNRI, serotonin–noradrenalin reuptake inhibitors; TCA, tricyclic antidepressants.

Table 2 Descriptions of symptoms and signs in both feet, and diagnostic test results used to verify DPN in the medical records

Use of the following descriptions/terms of symptoms and signs in both feet and test results in the medical record were used to verify DPN

Numbness

Prickling/tingling

Paresthesia

Hypoesthesia

Hypalgesia

Hyperalgesia/allodynia

Dysesthesia

Self-reported insensitivity or decreased sensitivity (eg “the patient reports decreased sensitivity in her feet”)

Self-reported description of inability to differentiate between warm/cold

Abnormal prick-sensation/abnormal pinprick

Abnormal temperature

Abnormal vibration

Abnormal light touch

Abnormal position

Physician described “decreased sensitivity”

Positive nerve conduction test (by physician interpretation/conclusion)

Physician documented diabetic polyneuropathy (eg “T2D patient with known complications including diabetic polyneuropathy, retinopathy.”)

Neuropathic pain (described below)

Neuropathic pain – use of the following descriptions for pain in both feet the medical record were used to verify painful DPN

Burning pain

Pins/needles or stabbing pain

Shooting pain

Squeezing pain

Prickling/tingling described painful

Other neuropathic pain (to capture less frequents used descriptions/terms)

Hyperalgesia/allodynia

Abbreviation: DPN, diabetic polyneuropathy.

Table 3 Descriptive data of hospital contacts of potential painful and non-painful DPN and potential diabetic foot ulcer identified using ICD-10 hospital codes and/or surgery in the DNPR and prescription codes in the NHSPD from 2009 to 2016

	Painful DPN, N=53	Non-painful DPN, N=54	Diabetic foot ulcer, N=53
Sex
Male	34 (64)	40 (74)	34 (64)
Female	19 (36)	14 (26)	19 (36)
Age, years
Median (quartiles)	64 (53–69)	67 (61–74)	74 (62–83)
Hospital type
University hospital	22 (42)	20 (37)	19 (36)
Regional hospital	31 (58)	34 (63)	34 (64)
Department type
Internal medicine	13 (25)	12 (22)	12 (23)
Neurological	9 (17)	15 (28)	1 (2)
Neurophysiological	22 (42)	18 (33)	0 (0)
Orthopaedic surgery	5 (9)	5 (9)	21 (40)
Vascular surgery	5 (8)	4 (7)	14 (26)
Dermatological	0 (0)	0 (0)	4 (8)
Plastic surgery	0 (0)	0 (0)	1 (2)
Admission type
Inpatient	9 (17)	13 (24)	16 (30)
Outpatient	44 (83)	41 (76)	37 (70)
Diabetic foot ulcer code type
Diagnosis code, only	N/A	N/A	26 (49)
Surgery code, only	N/A	N/A	18 (34)
Diagnosis+surgery code	N/A	N/A	9 (17)
Diagnosis code type^a
Primary diagnosis code	38 (72)	28 (52)	16 (30)
Secondary diagnosis code	16 (30)	26 (48)	19 (36)
Polyneuropathy – diagnosis code^b
E10.4-E14.4 (diabetes with neurological complication)	19 (36)	30 (56)	N/A
E10.4	2 (4)	8 (15)	N/A
E11.4	11 (21)	15 (28)	N/A
E12.4	0 (0)	0 (0)	N/A
E13.4	2 (4)	2 (4)	N/A
E14.4	4 (8)	5 (9)	N/A
DG62.9 (polyneuropathy, unspecified)	24 (45)	19 (35)	N/A
DG63.2 (diabetic polyneuropathy)	11 (21)	5 (9)	N/A
Type of neuropathic analgesics^c
Antiepileptic medicine
Gabapentin	21 (40)	0 (0)	N/A
Pregabalin	14 (26)	0 (0)	N/A
Lamotrigine	2 (4)	0 (0)	N/A
Valproic acid	1 (2)	0 (0)	N/A
Carbamazepine	2 (4)	0 (0)	N/A
Oxcarbazepine	0 (0)	0 (0)	N/A
Serotonin–noradrenalin reuptake inhibitors
Venlafaxine	1 (2)	0 (0)	N/A
Duloxetine	0 (0)	0 (0)	N/A
Tricyclic antidepressants		0 (0)	N/A
Imipramine	2 (4)	0 (0)	N/A
Clomipramine	0 (0)	0 (0)	N/A
Amitriptyline	23 (43)	0 (0)	N/A
Nortriptyline	6 (11)	0 (0)	N/A
Maprotiline	1 (2)	0 (0)	N/A
Diabetic foot ulcer – diagnosis and surgery codes^d
E10.5-E14.5 (DM with peripheral vascular complication)	N/A	N/A	26 (49)
L97 (ulcer of lower limb)	N/A	N/A	4 (8)
L98.4 (chronic skin ulcer, non specified)	N/A	N/A	5 (9)
R02 (gangrene)	N/A	N/A	0 (0)
M86 (osteomyelitis)	N/A	N/A	1 (2)
KQDA (puncture, incisions and local destructions of pathological tissue in the skin at the lower extremity)	N/A	N/A	2 (4)
KQDB (treatment of ulcer at lower extremity)	N/A	N/A	24 (45)
KQDG (operations for chronic ulcer/fistula at lower extremity)	N/A	N/A	2 (4)

Notes: ^aOne patient was discharged with an A- and a B-diagnosis that were both included in the polyneuropathy algorithm. Thus the percentage does not sum up to 100%. ^bOne patient was discharged with 2 different codes, that were both included in the in polyneuropathy algorithm. ^c39 patients had redeemed prescriptions of one type of ATC-code, 10 patients had redeemed prescriptions of two types of ATC-codes, 3 patents had redeemed prescriptions of three types of ATC-codes and 1 had redeemed prescriptions of five different types of ATC-codes. ^dEach patient may have been given one or more diagnosis codes and/or one or more surgery codes on the diabetic foot ulcer date.

Abbreviations: DPN; Diabetic polyneuropathy, ICD-10; International classification of diseases, version 10, DNPR; Danish National Patient Register, DHSPR; Danish Health Service Prescription Register, N/A; Not applicable, e.g. diabetic foot ulcer-defining codes not relevant for polyneuropathy groups and neuropathic pain treatment codes and polyneuropathy-defining codes not relevant for diabetic foot ulcer group.

Table 4 Numbers and positive predictive values of potential DPN and diabetic foot ulcer

	Potential painful DPN, N=53					Potential non-painful DPN, N=54					Potential diabetic foot ulcer, N=53
	Medical record review, conclusion			PPV (95% CI)		Medical record review, conclusion			PPV (95% CI)		Medical record review, conclusion		PPV (95% CI)
	Non-painful DPN	Painful DPN	Not DPN^a	DPN	Painful DPN	Non-painful DPN	Painful DPN	Not DPN^a	DPN	Non-painful DPN	Diabetic foot ulcer	Not diabetic foot ulcer
Total	19	19	15	72 (58–83)	36 (23–50)	27	3	24	56 (41–69)	50 (36–64)	18	35	34 (22–48)
All G-codes and primary E-codes^b	17	18	10	78 (63–89)	40 (24–54)	22	3	9	74 (56–87)	65 (47–80)	-	-	-
All G-codes	15	15	5	86 (70–95)	43 (26–61)	16	1	7	71 (49–87)	67 (45–84)	-	-	-

Notes: ^aEither not polyneuropathy or polyneuropathy is likely caused by other diseases. ^bSecondary E-codes often denoted stroke or mononeuropathies.

Abbreviations: DPN, diabetic polyneuropathy; PPV, positive predictive value.