Sapropterin trial, part 2: Baseline testing

Sapropterin trial, part 2: Baseline testing
Photo by Maxim Hopman / Unsplash

Baseline testing is a necessary period of control before starting on sapropterin. It ensures that your blood phe levels have stabilised before starting the medication. Importantly, it gives a baseline against which any response can be easily seen. During baseline testing, my blood spots changed from monthly to weekly. And, I needed to show at least 6 results which were:

  • between 300umol/L and 600umol/L and,
  • within 100umol/L of each other

This would give the baseline figure against which the blood phe levels while I was on sapropterin would be tested.

Part one of the Sapropterin Blog series:

Sapropterin blood genetics test for PKU Phenylketonuria
A year after I went in for blood tests to determine if my PKU would respond, I finally took my first dose of sapropterin.
Click for part one in the series.

Lessons from Baseline testing

I was ready to start baseline testing in early December, the month of parties and food. While the testing could be delayed until the new year, I had already waited over 40 years for a treatment beyond restricted diet therapy. The desire to start immediately meant strict control over Christmas. Most years I would stick to the diet, but also have quite a few treats; like more potatoes, or extra sweets.

Not this year! Christmas and New Year’s became a time of searching out protein-free treats; including fruit jellies, PKU baking, and lots of exotic fruit. December and January were not easy, but I did learn more about my diet and attitude to it than I had in the past year. Most importantly, I learned that I had never done something quite like this before.

I knew that the control needed to reach the six blood phe levels required for baseline testing would be difficult. When I checked the list of my bloodspot results from the last 30 odd years, I discovered that I’d come close to managing that once in three decades. I knew that maintaining this level of control would be a tough ask. But what I didn’t know was that when I thought I had been strict on my diet in the past, I really hadn’t.

Blood phe can be too low

The requirement to weigh all my food and record every exchange & supplement across a month gave me the best control I’d ever had. Usually, when I was being strict, I would not quite record every exchange. Instead, I’d convince myself that I would remember it. Or that a little extra at supper wouldn’t change things too much. Or I wouldn’t weigh portions and just eyeball the amount.

In the three years running up to the baseline testing, my average levels were 500umol/L. During testing, two days before Christmas, my level was 104umol/L. My lowest blood result ever.

In the first four weeks of baseline testing, my levels were between 300umol/L and 100umol/L. After an initial burst of planning, the organisation to get these levels was not terribly different from before the control period. The focus on my diet actually felt good, as I was doing it with purpose. Physically, I had more energy and my head felt clearer on these lower levels.

That is interesting, and something I want to explore in the future. However, those levels were too low for the baseline trial. Indeed, after my result of 104, the clinic called to check I was okay. It is possible for blood phe levels to be too low, as well as too high.

Protein allowance increase without sapropterin

I have heard from others who had to increase exchanges during the baseline testing, and before starting on sapropterin. And, like them, I had wondered why. Now, I was experiencing it myself.

The level of control I was showing to get my levels down below 200 consistently, meant there wasn’t enough leeway to show a response to sapropterin when I eventually started the medication. I needed higher levels, so the clinic increased my exchange limit. My phe allowance increased by two exchanges, from 5g of protein every day to 7g. This was a wonder to me, as other people on low exchanges will know.

I was suddenly allowed more daily protein than I’d ever been on in the past. And I hadn’t even tried sapropterin yet. How did that happen? I think the increase in exchanges happened because, in the past, I hadn’t actually been recording my diet properly. This meant I was having those extra 2 exchanges in snacks and extra helpings, but I wasn’t recording them.

Now I had permission from the clinic, so I could have those two exchanges without guilt. As long as I recorded them carefully! The good news is that, whether I respond to sapropterin or not, I should be able to keep those extra two exchanges. As long as I don’t revert to my unintentional ‘no need to record them, she’ll be right’ attitude.

Reducing hunger on PKU

I started taking (and recording!) the extra two exchanges and noticed a change in my hunger levels immediately. That was interesting, given I had probably been having those two exchanges in an unplanned manner already. I could now plan my food to incorporate those exchanges across the whole day.

Instead of using those two exchanges on unplanned afternoon snacks, or rationalising them as ‘just a little extra’, I spent a cold January having those two extra exchanges planned across the day. Breakfast, lunch, and dinner were now 2 phe each. And the final exchange was held back in case of an unforeseen office biscuit tin, or an oat milk latte with a friend. If I hadn’t used it by then end of the day, I had a small supper.

It might seem like a small change, but the increase in phe at breakfast meant I could last the entire morning without hunger pangs. The same happened in the afternoon, and I soon found I wasn’t having my elevenses and afternoon snacks. The increase in exchanges alone was worth the months of weekly bloodspots and weighing.

11 weeks of control before sapropterin

It took me 11 weeks to get a baseline level of six blood tests which were between 300 and 600umol/L, and which were within 100umol/L of each other. It was not easy. I skipped events, pub lunches, evenings out, visits to friend’s places… Basically, I didn’t go anywhere that I could not be sure of the exact content of protein in my food.

However, I finally reached the baseline requirements almost exactly a year after undergoing blood tests for genetic testing. It had taken patience, perseverance, the encouragement of others in the PKU community. But I could finally start on a sapropterin trial.

Note: the three years before baseline testing, I had been on 5 exchanges and I thought I had a strict control. Over those 3 years, my average blood phe level was 500umol/L. During the ‘strictly recorded and measured’ 7 exchange regime, my average blood level was 490umol/L. This, and the fact that I knew I was guilty of being a little loose sometimes, is what leads me to believe that I had been having the extra 2 phe previously, and was simply not recording them carefully.