Service evaluation of a clinical scientist-led cystinuria clinic

Cystinuria is an autosomal recessive genetic disease, reducing the reabsorption of dibasic amino acids, which leads to the formation of cystine stones in the kidneys, ureters and bladder. ¹ The condition has a high morbidity, as stones are frequently passed, and removal of stones requires multiple surgical procedures. Age of onset is typically within the first 2 decades of life and severity of clinical symptoms varies between patients. ¹

Treatment for cystinuria is mainly preventative. It is recommended cystinuria patients drink more than 3 L fluid a day to dilute cystine in their urine. ² They are advised to avoid eating animal protein and to restrict salt intake ³ to reduce cystine excretion. Increasing urine pH increases the solubility of cystine and therefore reduces stone formation. Therefore, urine alkalinisation is a beneficial preventative measure for these patients. Urine can by alkalinised by potassium citrate or sodium bicarbonate. ³

The Urine pH clinic was set up at the Liverpool University Hospitals to allow patients to monitor the pH of their own urine and make sure they are in the target range (pH 7–8). Patients are trained by a clinical scientist to use a pH metre (Hanna Instruments HI98127 waterproof pH metre) to record urine pH. This is a robust method and is clinically validated. ⁴

The patients are asked to complete logbooks with their urine pH for 24 h, performing QC at the beginning of the day. They record the pH of each urine passed as well as the volume, the time, and the time they take any medication. Renal function and potassium levels are also monitored at each clinic appointment.

Data from 19 patients’ pH logbooks over 8 years (2014–2021) were retrospectively analysed to evaluate the benefit for patients attending the urine pH clinic. Data included urine pH and volume, medication and kidney stone recurrence.

Patient questionnaires were designed using SurveyMonkey and contained 8 questions about their experience of the clinic, how easy they found the urine pH metre to use and if they had noticed any improvement in their condition since attending the pH clinic. Questionnaires were sent to patients and were available to complete at the clinic.

Table 1 shows the patients attending the clinic and their urine pH, urine volume and kidney stone formation for their first and last (or most recent) year of attendance. For those patients that were below target urine pH it was highlighted whether those patients were on the maximum dose of medication available (>3 doses of potassium citrate and/or sodium bicarbonate per day).

Table 1.

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Patient	Years attending clinic	First year attending clinic			Final/most recent year attending clinic			pH > 7
		Average urine pH	Average urine volume	Average no. Stones	Average urine pH	Average urine volume	Average no. Stones
A	1	6.2	1893	3	X	X	X	N*
B	2	7	3551	1	7.1	3083	0	Y
C	2	6.8	2300	3	6.6	3245	2	N*
D	2	7.2	NB	0	7.4	2500	0	Y
E	2	6.7	4500	0	7.1	3198	0	Y
F	3	6.7	2620	1	6.6	2500	0	N*
G	3	7.5	2750	0	6.9	3590	1	N*
H	3	7	3443	0	6.3	2595	1	N*
I	4	NB	NB	0	6.8	NB	0	N*
J	4	7.5	3755	0	7.2	4850	0	Y
K	4	6.3	3000	1	6.8	3500	0	N
L	5	6.8	3250	1	7	2530	1	Y
M	5	7.1	3861	2	7.4	3620	0	Y
N	5	7.2	3950	0	7.5	3725	0	Y
O	5	6.7	2443	2	6.7	3855	3	N*
P	6	7.5	3359	0	7.4	3650	0	Y
Q	6	6.8	3975	0	6.9	4225	0	N*
R	7	7.2	4725	0	7.3	3030	0	Y
S	8	7.3	3000	0	7.2	4350	0	Y

Table 1 shows the average urine pH, urine volume and number of stones developed during the first and last/most recent year attending the clinic. The number of years that the patient has attended for is also shown. *The patient is outside the pH target range (pH >7) but they are on the highest medication dose or are known non-compliant. NB: Missing data, patients not filled in logbook.

The data indicates that patients are able to maintain or improve their urine pH whilst attending the clinic. For patients that have not met target, this may be because they are already on the maximum dose of alkalinising agents available and so cannot improve their urine pH further due to poor kidney function or tolerance. In one case the patient was known to have poor compliance with their medication. Average urine volume increased each year of clinic attendance which is beneficial to patients as maintaining high fluid volume dilutes the cystine and so reduces the risk of stone formation. ⁵

There were 10 responses to patient questionnaires. 100% of respondents stated that they found the pH metre ‘easy’ or ‘very easy’ to use. When asked about their overall experience of their condition, 60% said their condition had ‘improved’ or ‘improved a lot’. The rest said there was no change. All respondents stated that they found self-monitoring either ‘helpful’ or ‘very helpful’. Most patients (78%) wanted increased frequency of clinics or were satisfied with the number of clinic appointments they receive.

The patient feedback highlighted the support the clinic provides and how patients feel it is useful for them to be able to manage their condition themselves. To increase the frequency of clinics, plans have been made to acquire more pH metres. This will improve patient experience as most patients asked for this in their feedback.

The clinic is entirely managed by clinical scientists, with oversight from medical consultants, from scheduling appointments to meeting patients face-to-face in clinic. This is the first such clinic set up at the Liverpool University Hospitals and has been shown to be a success, freeing up clinician’s time and expanding the role of clinical scientists.

The urine pH clinic has been evaluated by cystinuria patients as a beneficial service and this has been corroborated by the biochemical results which have been shown to reduce the significant morbidities faced by this patient group.