"I think you may have HIV."

I searched his eyes for a reaction. There was no shock, no disbelief, no hint of worry. I glanced at his wife and found the same blank stare.

The whistling ceiling fan was the only thing that broke the silence in a room that smelled stale in the 37 deg C heat of midday. I was treating ethnic Karen refugees in a small mission hospital in a dusty border town in Thailand, 12km from the Myanmar border. I had seen many of those blank stares that week. That day, however, I realised why this look was strangely familiar to me.

Miles away, in the sterile air-conditioned hospitals in Singapore, I had seen the same look in a patient. We had told him: "If you continue refusing to let us help you, you are going to die of Aids." He did not seem to care. It was an inexplicable indifference.

Those of us who treated Weirong for Aids in Singapore never understood his choices in life. At home, anti-retroviral therapy (ART) is still expensive for patients, even after recent government policies that have reduced its cost. Weirong was in his 30s when our paths crossed. Social workers had worked tirelessly to help him find funding for his treatment. The entire hospital's infectious diseases department knew him. He was notorious for refusing treatment plans and medication. I was warned before our first meeting. He was prone to histrionics, but had the gift of an affable and disarming grin. There was a polite vulnerability in his voice that helped him ingratiate himself when negotiating with us.

We negotiated every day. Blood- taking was an hour-long debate. Despite our best efforts, he refused the treatment we recommended, choosing to distrust us and believe instead in home remedies recommended by a blogger with a dubious PhD. One day, out of desperation, we told him plainly that he was wilfully dying of Aids. He was resolute and continued to refuse the life-saving antivirals we recommended. It was frustrating to see the contradictions in this man. How could he pride himself on reason yet make these stubborn and irrational choices? How could he be told his life was ending yet remain indifferent to death?

When Moe was diagnosed with Aids, it should not have come as a shock to the medical staff in the mission hospital near Sangkhlaburi in the Kanchanaburi province of Thailand. He, too, was in his 30s. Eight years ago, he had been diagnosed with multi-drug resistant tuberculosis (MDRTB) in a place populated mostly by Karen refugees. They flee war from across the border only to end up in poverty here.

This is one of many villages dotting the border of West Thailand. Its yellow soil and bamboo huts are a far cry from the gleaming skyscrapers and mega malls of downtown Bangkok. We are near refugee camps that are hotbeds for the spread of MDRTB. Even if the Karen residents from this tiny refugee outpost make it to a big city hospital, without citizenship or health insurance, there is not much treatment they can receive. Yet this village hospital, which serves an area with a radius of 200km and which extends to Myanmar, has access to The Global Fund. Veteran healthcare staff dispense TB medication with the help of a resilient network of community workers to enforce Directly Observed Therapy (DOT), a way to ensure TB patients take all their medication.

For seven months Moe was compliant to treatment and regained weight. Two months short of completing it, he disappeared. Community workers went to his house many times but he was simply gone. Here is one man who had a chance of survival against all odds but threw it away. It is a frustrating thought. Yet he is but one of many.

Now, he walks casually into the clinic looking his weight of 38kg after two months of not eating. There is pain every time he tries to swallow and the sensation extends down to his stomach. It has been getting worse and now he can take only liquids. His temples are sunken in and the grooves between his knuckles appear deeper than the valleys of this mountainous terrain. He comes in with his wife, a young woman who also looks wasted and older than her years. I suppress a wince as he tells me about their two-year-old child, and then about his first wife and the six-year-old child they have. I ask him why he went away when his MDRTB treatment was incomplete. He says he went away for work.

I ask him to open his mouth so I can check for leukoplakia, and as he painfully parts his lips, I hope that perhaps I am wrong and that the constellation of wasting, a history of poor compliance with MDRTB treatment and a complicated social history are just coincidences in his story and that he does not have Aids. But I shine my torch down his throat and I see an unmistakable whiteness insidiously creeping from the back of his tongue to the roof of his mouth and surely all the way down his gut. It is one of the many faces of the monster that is devouring his life, and possibly his wives' and his children's. I take a deep breath, for myself, and let out a foreboding, audible sigh for the benefit of my interpreter.

To break the news gently, I frame the problem that he came in with and hint at an unpleasant conclusion. By the time I say, "I need to test you for HIV", I see Moe nod even before the interpreter has finished translating. I look at him and his wife and I see indifference staring back at me.

At this moment, I see precisely the frustration that plagues and exhausts many well-meaning doctors. We chide our patients for not turning up earlier with such disturbing symptoms so that our efforts will not be too little, too late. We practise in societies, both rich and poor, where the governments' coffers have limits and we navigate policies or squeeze money dry from funds to get our patients the medication they need. We ration strained resources for our patients no matter where we are.

In Singapore, we grapple with when to let a terminally ill patient in critical care go, so as to make way for another with a reversible illness. At the Thai-Myanmar border, we struggle when a patient comes in, skin and bones, harbouring an opportunistic infection and asking for ART after having defaulted on treatment because she married and moved. Do we give precious treatment to someone who will die soon anyway, or save it for another but live with telling her there is no medicine we can give? We are exhausted that after all of the difficult decisions made while fighting for them, we are made to come face-to-face with some who do not seem to care.

On Dec 1, World Aids Day, Weirong passed away in Singapore. I entered his room to bid him farewell. His family was there and in shock. Again, against our advice, he had refused to disclose his diagnosis to them. There on his bed, his mother was sprawled prone next to him, her hand on his chest, her face next to his, wailing. From the foot of the bed, I squinted, and I saw beneath his non-rebreather mask and for the first time since I caught him absconding from the wards and throughout our long conversations since then - a restful smile.

Now in Thailand, I am confronted by Moe. I know nothing I do or say will ensure that Moe returns for an HIV test. There are no more laboratory services that day, as I have over-run a Saturday clinic in this small town. CD 4 counts (a laboratory test that tracks disease severity usually done on demand in developed areas) are done only once a month here and are sent to a lab hours away.

If he returns, we will overcome the logistical and funding limitations to get him the help he needs. We can save even more lives if he brings his wife and children along for testing. And yet, although doctors often refuse to admit it, the truth is that we cannot control our patients. The outcome depends not on what we want for them but what they want for themselves.

Moe returns on Monday for his test and we find out that his wife already knows she is HIV-positive.

Our patients know more than we think; and their social lives are perhaps less simple than we assume. I was naive to think otherwise.

Still, they face battles that some of us cannot even imagine. We think it reckless to throw away a life for a job, or a lover. But do we know what life is like when one has to walk 200km to find the nearest clinic? Who are we to judge when some view the loneliness or the loss of individuality as more unbearable than the illness itself?

This indifference to the gravity of their illness belies a daily struggle to survive, where the fight to keep one's identity, and against poverty, loneliness and war are more relevant and pressing reminders of mortality.

We pride ourselves on upholding medical professionalism and ethics, working hard and following the best guidelines while making do with limited resources in places rich and poor. Contrary to popular belief, the road to satisfaction is not paved solely with one's efforts or the latest technology; life is not supposed to revolve around a disease or a hospital. But if we accept our losses and the indifference of our patients, then we will also be able to put aside the need to seek rewards and recognition for our work.

Then, we will be able to look beyond ourselves to see our patient's quest for autonomy, to understand that his indifference reveals his personal struggle to live a life fraught with ignominious battles. Only then can we start to respect our patient for who he is, or was.

• The names of patients have been changed to protect their identity.
• The writer is a medical doctor from Singapore with experience volunteering in South-east Asia. She has spent the past year living in Thailand.